Research: Sexual Orientation
Sexual Orientation
While some people are under the impression that sexual orientation
is an innate, fixed, and biological trait of human beings — that, whether
heterosexual, homosexual, or bisexual, we are “born that way” — there is
insufficient scientific evidence to support that claim. In fact, the concept of
sexual orientation itself is highly ambiguous; it can refer to a set of
behaviors, to feelings of attraction, or to a sense of identity.
Epidemiological studies show a rather modest association between genetic
factors and sexual attractions or behaviors, but do not provide significant
evidence pointing to particular genes.
There is also evidence for other
hypothesized biological causes of homosexual behaviors, attractions, or
identity — such as the influence of hormones on prenatal development — but that
evidence, too, is limited. Studies of the brains of homosexuals and
heterosexuals have found some differences, but have not demonstrated that these
differences are inborn rather than the result of environmental factors that
influenced both psychological and neurobiological traits.
One environmental
factor that appears to be correlated with non-heterosexuality is childhood
sexual abuse victimization, which may also contribute to the higher rates of
poor mental health outcomes among non-heterosexual subpopulations, compared to
the general population. Overall, the evidence suggests some measure of fluidity
in patterns of sexual attraction and behavior — contrary to the “born that way”
notion that oversimplifies the vast complexity of human sexuality.
The popular discussion of sexual orientation is characterized by
two conflicting ideas about why some individuals are lesbian, gay, or bisexual.
While some claim that sexual orientation is a choice, others say that sexual
orientation is a fixed feature of one’s nature, that one is “born that way.” We
hope to show here that, though sexual orientation is not a choice, neither is
there scientific evidence for the view that sexual orientation is a fixed and innate
biological property.
A prominent recent example of a person describing sexual
orientation as a choice is Cynthia Nixon, a star of the popular television
series Sex and the City,
who in a January 2012 New York
Times interview explained,
“For me it’s a choice, and you don’t get to define my gayness for me,” and
commented that she was “very annoyed” about the issue of whether or not gay
people are born that way. “Why can’t it be a choice? Why is that any less
legitimate?”[1] Similarly, Brandon Ambrosino wrote in The New Republic in 2014 that “It’s time for the LGBT
community to stop fearing the word ‘choice,’ and to reclaim the dignity of
sexual autonomy.”[2]
By contrast, proponents of the “born that way” hypothesis —
expressed for instance in Lady Gaga’s 2011 song “Born This Way” — posit that
there is a causal biological basis for sexual orientation and often try to
bolster their claims with scientific findings. Citing three scientific studies[3] and an article from Science magazine,[4] Mark Joseph Stern, writing for Slate in 2014, claims that “homosexuality,
at least in men, is clearly, undoubtedly, inarguably an inborn trait.”[5] However, as neuroscientist Simon
LeVay, whose work in 1991 showed brain differences in homosexual men compared
to heterosexual men, explained some years after his study, “It’s important to
stress what I didn’t find. I did not prove that homosexuality is genetic, or
find a genetic cause for being gay. I didn’t show that gay men are ‘born that
way,’ the most common mistake people make in interpreting my work. Nor did I
locate a gay center in the brain.”[6]
Many recent books contain popular treatments of science that make
claims about the innateness of sexual orientation. These books often exaggerate
— or at least oversimplify — complex scientific findings. For example, in a
2005 book, psychologist and science writer Leonard Sax responds to a worried
mother’s question as to whether her teenage son will outgrow his homosexual
attractions: “Biologically, the difference between a gay man and a straight man
is something like the difference between a left-handed person and a
right-handed person. Being left-handed isn’t just a phase. A left-handed person
won’t someday magically turn into a right-handed person.... Some children are
destined at birth to be left-handed, and some boys are destined at birth to
grow up to be gay.”[7]
As we argue in this
part of the report, however, there is little scientific evidence to support the
claim that sexual attraction is simply fixed by innate and deterministic
factors such as genes. Popular understandings of scientific findings often
presume deterministic causality when the findings do not warrant that
presumption.
Another important
limitation for research and for interpretation of scientific studies on this
topic is that some central concepts — including “sexual orientation” itself —
are often ambiguous, making reliable measurements difficult both within
individual studies and when comparing results across studies. So before turning
to the scientific evidence concerning the development of sexual orientation and
sexual desire, we will examine at some length several of the most troublesome
conceptual ambiguities in the study of human sexuality in order to arrive at a
fuller picture of the relevant concepts.
A 2014 New York
Times Magazine piece titled
“The Scientific Quest to Prove Bisexuality Exists”[8]provides
an illustration of the themes explored in this Part — sexual desire,
attraction, orientation, and identity — and of the difficulties with defining
and studying these concepts. Specifically, the article shows how a scientific
approach to studying human sexuality can conflict with culturally prevalent
views of sexual orientation, or with the self-understanding that many people
have of their own sexual desires and identities. Such conflicts raise important
questions about whether sexual orientation and related concepts are as coherent
and well-defined as is often assumed by researchers and the public alike.
The author of the
article, Benoit Denizet-Lewis, an openly gay man, describes the work of
scientists and others trying to demonstrate the existence of a stable bisexual
orientation. He visited researchers at Cornell University and participated in
tests used to measure sexual arousal, tests that include observing the way
pupils dilate in response to sexually explicit imagery. To his surprise, he
found that, according to this scientific measure, he was aroused when watching
pornographic films of women masturbating:
Might I actually be bisexual? Have I been so wedded to my gay
identity — one I adopted in college and announced with great fanfare to family
and friends — that I haven’t allowed myself to experience another part of
myself? In some ways, even asking those questions is anathema to many gays and
lesbians. That kind of publicly shared uncertainty is catnip to the Christian
Right and to the scientifically dubious, psychologically damaging ex-gay
movement it helped spawn. As out gay men and lesbians, after all, we’re
supposed to be sure — we’re supposed to be “born this way.”[9]
Despite the apparently scientific (though admittedly limited)
evidence of his bisexual-typical patterns of arousal, Denizet-Lewis rejected
the idea that he was actually bisexual, because “It doesn’t feel true as a
sexual orientation, nor does it feel right as my identity.”[10]
Denizet-Lewis’s
concerns here illustrate a number of the quandaries raised by the scientific
study of human sexuality. The objective measures the researchers used seemed to
be at odds with the more intuitive, subjective understanding of what it is to
be sexually aroused; our own understanding of what we are sexually aroused by
is tied up with the entirety of our lived experience of sexuality. Furthermore,
Denizet-Lewis’s insistence that he is gay, not bisexual, and his concern that
uncertainty about his identity could have social and political implications,
points to the fact that sexual orientation and identity are understood not only
in scientific and personal terms, but in social, moral, and political terms as
well.
But how do
categories of sexual orientation — with labels such as “bisexual” or “gay” or
“straight” — help scientists study the complex phenomenon of human sexuality?
When we examine the concept of sexual orientation, it becomes apparent, as this
part will show, that it is too vague and poorly defined to be very useful in
science, and that in its place we need more clearly defined concepts. We strive
in this report to use clear terms; when discussing scientific studies that rely
on the concept of “sexual orientation,” we try as much as possible to specify
how the scientists defined the term, or related terms.
One of the central
difficulties in examining and researching sexual orientation is that the
underlying concepts of “sexual desire,” “sexual attraction,” and “sexual
arousal” can be ambiguous, and it is even less clear what it means that a
person identifies as having a sexual orientation grounded in some pattern of
desires, attractions, or states of arousal.
The word “desire” all by itself might be used to cover an aspect
of volition more naturally expressed by “want”: I want to go out for dinner, or
to take a road trip with my friends next summer, or to finish this project.
When “desire” is used in this sense, the objects of desire are fairly
determinate goals — some may be perfectly achievable,
such as moving to a new city or finding a new job; others may be more ambitious
and out of reach, like the dream of becoming a world-famous movie star. Often,
however, the language of desire is meant to include things that are less clear:
indefinite longings for a life that is, in some
unspecified sense, different or better; an inchoate sense of something being
missing or lacking in oneself or one’s world; or, in psychoanalytic literature,
unconscious dynamic forces that shape one’s cognitive, emotional, and social
behaviors, but that are separate from one’s ordinary, conscious sense of self.
This more
full-blooded notion of desire is, itself, ambiguous. It might refer to a
hoped-for state of affairs like finding a sense of meaning, fulfillment, and
satisfaction with one’s life, a desire that, while not completely clear in its
implications, is presumably not entirely out of reach, although such longings
may also be forms of fantasizing about a radically altered or perhaps even
unattainable state of affairs. If I want to take a road trip with my friends,
the steps are clear: call up my friends, pick a date, map out a route, and so
on. However, if I have an inchoate longing for change, a hope for sustainable
intimacy, love, and belonging, or an unconscious conflict that is disrupting my
ability to move forward in the life I have tried to build for myself, I face a
different sort of challenge. There is not necessarily a set of well-defined or
conscious goals, much less established ways of achieving them. This is not to
say that the satisfaction of these longings is impossible, but doing so often
involves not only choosing concrete actions to achieve particular goals but the
more complex shaping of one’s own life through acting in and making sense of
the world and one’s place in it.
So the first thing
to note when considering both popular discussions and scientific studies of
sexuality is that the use of the term “desire” could refer to distinct aspects
of human life and experience.
Just as the meanings that might be intended by the term “desire”
are many, so also is each of these meanings varied, making clear delineations a
challenge. For example, a commonsense understanding might suggest that the term
“sexual desire” means wanting to engage in specific sexual acts with particular
individuals (or categories of individuals). Psychiatrist Steven Levine
articulated this common view in his definition of sexual desire as “the sum of
the forces that incline us toward and away from sexual behavior.”[11] But it is not obvious how one might
study this “sum” in a rigorous way. Nor is it obvious why all the diverse
factors that can potentially influence sexual behavior, such as material
poverty — in the case of prostitution, for instance — alcohol consumption, and
intimate affection, should all be grouped together as aspects of sexual desire.
As Levine himself points out, “In anyone’s hands, sexual desire can be a slippery
concept.”[12]
Consider a few of
the ways that the term “sexual desire” has been employed in scientific contexts
— designating one or more of the following distinct phenomena:
1. States of
physical arousal that may or may not be linked to a specific physical activity
and may or may not be objects of conscious awareness.
2. Conscious erotic
interest in response to finding others attractive (in perception, memory, or
fantasy), which may or may not involve any of the bodily processes associated
with measurable states of physical arousal.
3. Strong interest
in finding a companion or establishing a durable relationship.
4. The romantic aspirations
and feelings associated with infatuation or falling in love with a specific
individual.
5. Inclination
towards attachment to specific individuals.
6. The general
motivation to seek intimacy with a member of some specific group.
7. An aesthetic measure that latches onto perceived beauty in
others.[13]
In a given social science study, the concepts mentioned above will
often each have its own particular operational definition for the purposes of
research. But they cannot all mean the same thing. Strong interest in finding a
companion, for example, is clearly distinguishable from physical arousal.
Looking at this list of experiential and psychological phenomena, one can
easily envision what confusions might arise from using the term “sexual desire”
without sufficient care.
The philosopher
Alexander Pruss provides a helpful summary of some of the difficulties involved
in characterizing the related concept of sexual attraction:
What does it mean to be “sexually attracted” to someone? Does it
mean to have a tendency to be aroused in their presence? But surely it is
possible to find someone sexually attractive without being aroused. Does it mean
to form the belief that someone is sexually attractive to one? Surely not,
since a belief about who is sexually attractive to one might be wrong — for
instance, one might confuse admiration of form with sexual attraction. Does it
mean to have a noninstrumental desire for a sexual or romantic relationship
with the person? Probably not: we can imagine a person who has no sexual
attraction to anybody, but who has a noninstrumental desire for a romantic
relationship because of a belief, based on the testimony of others, that
romantic relationships have noninstrumental value. These and similar questions
suggest that there is a cluster of related concepts under the head of “sexual
attraction,” and any precise definition is likely to be an undesirable shoehorning.
But if the concept of sexual attraction is a cluster of concepts, neither are
there simply univocal concepts of heterosexuality, homosexuality, and
bisexuality.[14]
The ambiguity of the term “sexual desire” (and similar terms)
should give us pause to consider the diverse aspects of human experience that
are often associated with it. The problem is neither irresolvable nor unique to
this subject matter. Other social science concepts — aggression and addiction,
for example — may likewise be difficult to define and to operationalize and for
this reason admit of various usages.[*] Nevertheless, the ambiguity presents a
significant challenge for both research design and interpretation, requiring
that we take care in attending to the meanings, contexts, and findings specific
to each study. It is also important to bracket any subjective associations with
or uses of these terms that do not conform to well-defined scientific
classifications and techniques.
It would be a
mistake, at any rate, to ignore the varied uses of this and related terms or to
try to reduce the many and distinct experiences to which they might refer to a
single concept or experience. As we shall see, doing so could in some cases
adversely affect the evaluation and treatment of patients.
We can further clarify the complex phenomenon of sexual desire if
we examine what relationship it has to other aspects of our lives. To do so, we
borrow some conceptual tools from a philosophical tradition known as
phenomenology, which conceives of human experience as deriving its meaning from
the whole context in which it appears.
The testimony of
experience suggests that one’s experience of sexual desire and sexual
attraction is not voluntary, at least not in any immediate way. The whole set
of inclinations that we generally associate with the experience of sexual
desire — whether the impulse to engage in particular acts or to enjoy certain
relationships — does not appear to be the sole product of any deliberate
choice. Our sexual appetites (like other natural appetites) are experienced as
given, even if their expression is shaped in subtle ways by many factors, which
might very well include volition. Indeed, far from appearing as a product of
our will, sexual desire — however we define it — is often experienced as a
powerful force, akin to hunger, that many struggle (especially in adolescence)
to bring under direction and control. Furthermore, sexual desire can impact
one’s attention involuntarily or color one’s day-to-day perceptions,
experiences, and encounters. What seems to be to some extent in our control is
how we choose to live with this appetite, how we integrate it into the rest of
our lives.
But the question remains: What is sexual desire? What is this part of
our lives that we consider to be given, prior even to our capacity to
deliberate and make rational choices about it? We know that some sort of sexual
appetite is present in non-human animals, as is evident in the mammalian
estrous cycle; in most mammalian species sexual arousal and receptivity are
linked to the phase of the ovulation cycle during which the female is
reproductively receptive.[15] One of the relatively unique features
ofHomo sapiens, shared with only a few other primates, is that sexual
desire is not exclusively linked to the woman’s ovulatory cycle.[16] Some biologists have argued that this
means that sexual desire in humans has evolved to facilitate the formation of
sustaining relationships between parents, in addition to the more basic
biological purpose of reproduction. Whatever the explanation for the origins
and biological functions of human sexuality, the lived experience of sexual
desires is laden with significance that goes beyond the biological purposes
that sexual desires and behaviors serve. This significance is not just a subjective
add-on to the more basic physiological and functional realities, but something
that pervades our lived experience of sexuality.
As philosophers who study the structure of conscious experience
have observed, our way of experiencing the world is shaped by our “embodiment,
bodily skills, cultural context, language and other social practices.”[17] Long before most of us experience
anything like what we typically associate with sexual desire, we are already
enmeshed in a cultural and social context involving other persons, feelings,
emotions, opportunities, deprivations, and so on. Perhaps sexuality, like other
human phenomena that gradually become part of our psychological constitution,
has roots in these early meaning-making experiences. If meaning-making is
integral to human experience in general, it is likely to play a key role in
sexual experience in particular. And given that volition is operative in these
other aspects of our lives, it stands to reason that volition will be operative
in our experience of sexuality too, if only as one of many other factors.
This is not to
suggest that sexuality — including sexual desire, attraction, and identity — is
the result of any deliberate, rational decision calculus. Even if volition
plays an important role in sexuality, volition itself is quite complex: many,
perhaps most, of our volitional choices do not seem to come in the form of
discrete, conscious, or deliberate decisions; “volitional” does not necessarily
mean “deliberate.” The life of a desiring, volitional agent involves many tacit
patterns of behavior owing to habits, past experiences, memories, and subtle
ways of adopting and abandoning different stances on one’s life.
If something like this way of understanding the life of a
desiring, volitional agent is true, then we do not deliberately “choose” the
objects of our sexual desires any more than we choose the objects of our other
desires. It might be more accurate to say that we gradually guide and give
ourselves over to them over the course of our growth and development. This
process of forming and reforming ourselves as human beings is similar to what
Abraham Maslow calls self-actualization.[18] Why should sexuality be an exception
to this process? In the picture we are offering, internal factors, such as our
genetic make-up, and external environmental factors, such as past experiences,
are only ingredients, however important, in the complex human experience of
sexual desire.
Just as the concept of “sexual desire” is complex and difficult to
define, there are currently no agreed-upon definitions of “sexual orientation,”
“homosexuality,” or “heterosexuality” for purposes of empirical research.
Should homosexuality, for example, be characterized by reference to desires to
engage in particular acts with individuals of the same sex, or to a patterned
history of having engaged in such acts, or to particular features of one’s
private wishes or fantasies, or to a consistent impulse to seek intimacy with
members of the same sex, or to a social identity imposed by oneself or others,
or to something else entirely?
As early as 1896, in a book on homosexuality, the French thinker
Marc-André Raffalovich argued that there were more than ten different types of
affective inclination or behavior captured by the term “homosexuality” (or what
he called “unisexuality”).[19] Raffalovich knew his subject matter up
close: he chronicled the trial, imprisonment, and resulting social disgrace of
the writer Oscar Wilde, who had been prosecuted for “gross indecency” with
other men. Raffalovich himself maintained a prolonged and intimate relationship
with John Gray, a man of letters thought to be the inspiration for Wilde’s
classic The Picture of Dorian
Gray.[20] We might also consider the vast
psychoanalytic literature from the early twentieth century on the topic of
sexual desire, in which the experiences of individual subjects and their
clinical cases are catalogued in great detail. These historical examples bring
into relief the complexity that researchers still face today when attempting to
arrive at clean categorizations of the richly varied affective and behavioral
phenomena associated with sexual desire, in both same-sex and opposite-sex
attractions.
We may contrast
such inherent complexity with a different phenomenon that can be delineated
unambiguously, such as pregnancy. With very few exceptions, a woman is or is
not pregnant, which makes classification of research subjects for the purposes
of study relatively easy: compare pregnant women with other, non-pregnant
women. But how can researchers compare, say, “gay” men to “straight” men in a
single study, or across a range of studies, without mutually exclusive and
exhaustive definitions of the terms “gay” and “straight”?
To increase
precision, some researchers categorize concepts associated with human sexuality
along a continuum or scale according to variations in pervasiveness,
prominence, or intensity. Some scales focus on both intensity and the objects
of sexual desire. Among the most familiar and widely used is the Kinsey scale,
developed in the 1940s to classify sexual desires and orientations using
purportedly measurable criteria. People are asked to choose one of the
following options:
0 - Exclusively heterosexual
1 - Predominantly heterosexual, only incidentally homosexual
2 - Predominantly heterosexual, but more than incidentally homosexual
3 - Equally heterosexual and homosexual
4 - Predominantly homosexual, but more than incidentally heterosexual
5 - Predominantly homosexual, only incidentally heterosexual
6 - Exclusively homosexual[21]
1 - Predominantly heterosexual, only incidentally homosexual
2 - Predominantly heterosexual, but more than incidentally homosexual
3 - Equally heterosexual and homosexual
4 - Predominantly homosexual, but more than incidentally heterosexual
5 - Predominantly homosexual, only incidentally heterosexual
6 - Exclusively homosexual[21]
But there are
considerable limitations to this approach. In principle, measurements of this
sort are valuable for social science research. They can be used, for example,
in empirical tests such as the classic “t-test,” which helps researchers
measure statistically meaningful differences between data sets. Many
measurements in social science, however, are “ordinal,” meaning that variables are
rank-ordered along a single, one-dimensional continuum but are not
intrinsically significant beyond that. In the case of the Kinsey scale, this
situation is even worse, because it measures the self-identification of
individuals, while leaving unclear whether the values they report all refer to
the same aspect of sexuality — different people may understand the terms
“heterosexual” and “homosexual” to refer to feelings of attraction, or to
arousal, or to fantasies, or to behavior, or to any combination of these. The
ambiguity of the terms severely limits the use of the Kinsey scale as an
ordinal measurement that gives a rank order to variables along a single,
one-dimensional continuum. So it is not clear that this scale helps researchers
to make even rudimentary classifications among the relevant groups using
qualitative criteria, much less to rank-order variables or conduct controlled
experiments.
Perhaps, given the inherent complexity of the subject matter,
attempts to devise “objective” scales of this sort are misguided. In a critique
of such approaches to social science, philosopher and neuropsychologist Daniel
N. Robinson points out
that “statements that lend themselves to different interpretation do not become
‘objective’ merely by putting a numeral in front of them.”[22] It may be that self-reported
identifications with culturally fraught and inherently complex labels simply
cannot provide an objective basis for quantitative measurements in individuals
or across groups.
Another obstacle for research in this area may be the popular, but
not well-supported, belief that romantic desires are sublimations of sexual
desires. This idea, traceable to Freud’s theory of unconscious drives, has been
challenged by research on “attachment theory,” developed by John Bowlby in the
1950s.[23] Very roughly, attachment theory holds
that later affective experiences that are often grouped under the general
rubric “romantic” are explained in part by early childhood attachment behaviors
(associated with maternal figures or caregivers) — not by unconscious, sexual
drives. Romantic desires, following this line of thought, might not be as
strongly correlated with sexual desires as is commonly thought. All of this is
to suggest that simple delineations of the concepts relating to human sexuality
cannot be taken at face value and that ongoing empirical research sometimes
changes or complicates the meanings of the concepts.
If we look at recent research, we find that scientists often use
at least one of three categories when attempting to classify people as
“homosexual” or “heterosexual”: sexual behavior;
sexual fantasies (or related emotional or affective
experiences); and self-identification (as “gay,” “lesbian,” “bisexual,”
“asexual,” and so forth).[24] Some add a fourth: inclusion in a
community defined by sexual orientation. Consider, for example, the American
Psychological Association’s definition of sexual orientation in a 2008 document
designed to educate the public:
Sexual orientation refers to an enduring pattern of emotional,
romantic and/or sexualattractions to
men, women or both sexes. Sexual orientation also refers to a person’s sense of identity based on those attractions, related behaviors, and membership in acommunity of others who share those attractions.
Research over several decades has demonstrated that sexual orientation ranges
along a continuum, from
exclusive attraction to the other sex to exclusive attraction to the same sex.[25] [Emphases added.]
One difficulty with
grouping these categories together under the same general rubric of “sexual
orientation” is that research suggests they often do not coincide in real life.
Sociologist Edward O. Laumann and colleagues summarize this point clearly in a
1994 book:
While there is a core group (about 2.4 percent of the total men
and about 1.3 percent of the total women) in our survey who define themselves as homosexual or bisexual, have
same-gender partners, and
express homosexual desires,
there are also sizable groups who do not consider themselves to be either
homosexual or bisexual but have had adult homosexual experiences or express
some degree of desire.... [T]his preliminary analysis provides unambiguous
evidence that no single number can be used to provide an accurate and valid
characterization of the incidence and prevalence of homosexuality in the population
at large. In sum, homosexuality is fundamentally a multidimensional phenomenon
that has manifold meanings and interpretations, depending on context and
purpose.[26] [Emphases added.]
More recently, in a
2002 study, psychologists Lisa M. Diamond and Ritch C. Savin-Williams make a
similar point:
The more carefully researchers map these constellations —
differentiating, for example, between gender identity and sexual identity, desire and behavior, sexualversus affectionate feelings, early-appearing versus
late-appearing attractions andfantasies, or social identifications and sexual profiles — the more complicated the picture
becomes because few individuals report uniform inter-correlations among these
domains.[27] [Emphases added.]
Some researchers acknowledge the difficulties with grouping these
various components under a single rubric. For example, researchers John C.
Gonsiorek and James D. Weinrich write in a 1991 book: “It can be safely assumed
that there is no necessary relationship between a person’s sexual behavior and
self-identity unless both are individually assessed.”[28] Likewise, in a 1999 review of research
on the development of sexual orientation in women, social psychologist Letitia
Anne Peplau argues: “There is ample documentation that same-sex attractions and
behaviors are not inevitably or inherently linked to one’s identity.”[29]
In sum, the complexities surrounding the concept of “sexual
orientation” present considerable challenges for empirical research on the
subject. While the general public may be under the impression that there are
widely accepted scientific definitions of terms such as “sexual orientation,”
in fact, there are not. Diamond’s assessment of the situation in 2003 is still
true today, that “there is currently no scientific or popular consensus on the
exact constellation of experiences that definitively ‘qualify’ an individual as
lesbian, gay, or bisexual.”[30]
It is owing to such
complexities that some researchers, for instance Laumann, proceed by
characterizing sexual orientation as a “multidimensional phenomenon.” But one
might just as well wonder whether, in trying to shoehorn this “multidimensional
phenomenon” into a single category, we are not reifying a concept that
corresponds to something far too plastic and diffuse in reality to be of much
value in scientific research. While labels such as “heterosexual” and
“homosexual” are often taken to designate stable psychological or even
biological traits, perhaps they do not. It may be that individuals’ affective,
sexual, and behavioral experiences do not conform well to such categorical
labels because these labels do not, in fact, refer to natural (psychological or
biological) kinds. At the very least, we should recognize that we do not yet
possess a clear and well-established framework for research on these topics.
Rather than attempting to research sexual desire, attraction, identity, and
behavior under the general rubric of “sexual orientation,” we might do better
to examine empirically each domain separately and in its own specificity.
To that end, this
part of our report considers research on sexual desire and sexual attraction,
focusing on the empirical findings related to etiology and development, and
highlighting the underlying complexities. We will continue to employ ambiguous
terms like “sexual orientation” where they are used by the authors we discuss,
but we will try to be attentive to the context of their use and the ambiguities
attaching to them.
Keeping in mind these reflections on the problems of definitions,
we turn to the question of how sexual desires originate and develop. Consider
the different patterns of attraction between individuals who report
experiencing predominant sexual or romantic attraction toward members of the
same sex and those who report experiencing predominant sexual or romantic
attraction toward members of the opposite sex. What are the causes of these two
patterns of attraction? Are such attractions or preferences innate traits,
perhaps determined by our genes or prenatal hormones; are they acquired by
experiential, environmental, or volitional factors; or do they develop out of
some combination of both kinds of causes? What role, if any, does human agency
play in the genesis of patterns of attraction? What role, if any, do cultural
or social influences play?
Research suggests
that while genetic or innate factors may influence the emergence of same-sex
attractions, these biological factors cannot provide a complete explanation,
and environmental and experiential factors may also play an important role.
The most commonly accepted view in popular discourse we mentioned
above — the “born that way” notion that homosexuality and heterosexuality are
biologically innate or the product of very early developmental factors — has
led many non-specialists to think that homosexuality or heterosexuality is in
any given person unchangeable and determined entirely apart from choices,
behaviors, life experiences, and social contexts. However, as the following
discussion of the relevant scientific literature shows, this is not a view that
is well-supported by research.
One powerful research design for assessing whether biological or
psychological traits have a genetic basis is the study of identical twins. If
the probability is high that both members in a pair of identical twins, who
share the same genome, exhibit a trait when one of them does — this is known as
the concordance rate — then one can infer that genetic factors are likely to be
involved in the trait. If, however, the concordance rate for identical twins is
no higher than the concordance rate of the same trait in fraternal twins, who
share (on average) only half their genes, this indicates that the shared
environment may be a more important factor than shared genes.
One of the pioneers of behavioral genetics and one of the first
researchers to use twins to study the effect of genes on traits, including sexual
orientation, was psychiatrist Franz Josef Kallmann. In a landmark paper
published in 1952, he reported that for all the pairs of identical twins he
studied, if one of the twins was gay then both were gay, yielding an
astonishing 100% concordance rate for homosexuality in identical twins.[31] Were this result replicated and the
study designed better, it would have given early support to the “born that way”
hypothesis. But the study was heavily criticized. For example, philosopher and
law professor Edward Stein notes that Kallmann did not present any evidence
that the twins in his study were in fact genetically identical, and his sample
was drawn from psychiatric patients, prisoners, and others through what
Kallmann described as “direct contacts with the clandestine homosexual world,”
leading Stein to argue that Kallmann’s sample “in no way constituted a
reasonable cross-section of the homosexual population.”[32] (Samples such as Kallmann’s are known
as convenience samples, which involve selecting subjects from populations that
are conveniently accessible to the researcher.)
Nevertheless, well-designed twin studies examining the genetics of
homosexuality indicate that genetic factors likely play some role in
determining sexual orientation. For example, in 2000, psychologist J. Michael
Bailey and colleagues conducted a major study of sexual orientation using twins
in the Australian National Health and Medical Research Council Twin Registry, a
large probability sample, which was therefore more likely to be representative of
the general population than Kallmann’s.[33] The study employed the Kinsey scale to
operationalize sexual orientation and estimated concordance rates for being
homosexual of 20% for men and 24% for women in identical (maternal,
monozygotic) twins, compared to 0% for men and 10% for women in non-identical
(fraternal, dizygotic) twins.[34] The difference in the estimated
concordance rates was statistically significant for men but not for women. On
the basis of these findings, the researchers estimated that the heritability of
homosexuality for men was 0.45 with a wide 95% confidence interval of
0.00–0.71; for women, it was 0.08 with a similarly wide confidence interval of
0.00–0.67. These estimates suggest that for males 45% of the differences
between certain sexual orientations (homosexual versus heterosexuals as
measured by the Kinsey scale) could be attributed to differences in genes.
The large confidence intervals in the study by Bailey and
colleagues mean that we must be careful in assessing the substantive
significance of these findings. The authors interpret their findings to suggest
that “any major gene for strictly defined homosexuality has either low
penetrance or low frequency,”[35] but their data did show (marginal)
statistical significance. While the concordance estimates seem somewhat high in
the models used, the confidence intervals are so wide that it is difficult to
judge the reliability, including the replicability, of these estimates.
It is worth
clarifying here what “heritability” means in these studies, since the technical
meaning in population genetics is narrower and more precise than the everyday
meaning of the word. Heritability is a measure of how much variation in a
particular trait within a population can be attributed to variation in genes in
that population. It is not, however, a measure of how much a trait is
genetically determined.
Traits that are almost entirely genetically determined can have
very low heritability values, while traits that have almost no genetic basis
can be found to be highly heritable. For instance, the number of fingers human
beings have is almost completely genetically determined. But there is little variationin the number of
fingers humans have, and most of the variation we do see is due to non-genetic
factors such as accidents, which would lead to low heritability estimates for
the trait. Conversely, cultural traits can sometimes be found to be highly
heritable. For instance, whether a given individual in mid-twentieth century
America wore earrings would have been found to be highly heritable, because it
was highly associated with being male or female, which is in turn associated
with possessing XX or XY sex chromosomes, making variability in earring-wearing
behavior highly associated with genetic differences, despite the fact that
wearing earrings is a cultural rather than biological phenomenon. Today,
heritability estimates for earring-wearing behavior would be lower than they
were in mid-twentieth century America, not because of any changes in the
American gene pool, but because of the increased acceptance of men wearing
earrings.[36]
So, a heritability
estimate of 0.45 does not mean that 45% of sexuality is determined by genes.
Rather, it means that 45% of the variation between individuals in the
population studied can be attributed in some way to genetic factors, as opposed
to environmental factors.
In 2010, psychiatric epidemiologist Niklas Långström and
colleagues conducted a large, sophisticated twin study of sexual orientation,
analyzing data from 3,826 identical and fraternal same-sex twin pairs (2,320
identical and 1,506 fraternal pairs).[37] The researchers operationalized
homosexuality in terms of lifetime same-sex sexual partners. The sample’s
concordance rates were somewhat lower than those found in the study by Bailey
and colleagues. For having had at least one same-sex partner, the concordance
for men was 18% in identical twins and 11% in fraternal twins; for women, 22%
and 17%, respectively. For total number of sexual partners, concordance rates
for men were 5% in identical twins and 0% in fraternal twins; for women, 11%
and 7%, respectively.
For men, these rates suggest an estimated heritability rate of
0.39 for having had at least one lifetime same-sex partner (with a 95%
confidence interval of 0.00–0.59), and 0.34 for total number of same-sex
partners (with a 95% confidence interval of 0.00–0.53). Environmental factors
experienced by one twin but not the other explained 61% and 66% of the
variance, respectively, while environmental factors shared by the twins failed
to explain any of the variance. For women, the heritability rate for having had
at least one lifetime same-sex partner was 0.19 (95% confidence interval of
0.00–0.49); for total number of same-sex partners, it was 0.18 (95% confidence
interval of 0.11–0.45). Unique environmental factors accounted for 64% and 66%
of the variance, respectively, while shared environmental factors accounted for
17% and 16%, respectively. These values indicate that, while the genetic
component of homosexual behavior is far from negligible, non-shared
environmental factors play a critical, perhaps preponderant, role. The authors
conclude that sexual orientation arises from both heritable and environmental
influences unique to the individual, stating that “the present results support
the notion that the individual-specific environment does indeed influence
sexual preference.”[38]
Another large and nationally representative study of twins
published by sociologists Peter S. Bearman and Hannah Brückner in 2002 used
data from the National Longitudinal Study of Adolescent to Adult Health
(commonly abbreviated as “Add Health”) of adolescents in grades 7–12.[39] They attempted to estimate the
relative influence of social factors, genetic factors, and prenatal hormonal
factors on the development of same-sex attractions. Overall, 8.7% of the 18,841
adolescents in their study reported same-sex attractions, 3.1% reported a
same-sex romantic relationship, and 1.5% reported same-sex sexual behavior. The
authors first analyzed the “social influence hypothesis,” according to which
opposite-sex twins receive less gendered socialization from their families than
same-sex twins or opposite-sex siblings, and found that this hypothesis was
well-supported in the case of males. While female opposite-sex twins in the
study were the least likely of all the groups to report same-sex attractions
(5.3%), male opposite-sex twins were the likeliest to report same-sex attractions
(16.8%) — more than twice as likely as males with a full, non-twin sister
(16.8% vs. 7.3%). The authors concluded there was “substantial indirect
evidence in support of a socialization model at the individual level.”[40]
The authors also examined the “intrauterine hormone transfer
hypothesis,” according to which prenatal hormone transfers between opposite-sex
twin fetuses influences the sexual orientation of the twins. (Note that this is
different from the more general hypothesis that prenatal hormones influence the
development of sexual orientation.) In the study, the proportion of male
opposite-sex twins reporting same-sex attraction was about twice as high for
those without older brothers (18.7%) as for those with older brothers (8.8%).
The authors argued that this finding was strong evidence against the
hormone-transfer hypothesis, since the presence of older brothers should not
decrease the likelihood of same-sex attraction if that attraction has a basis
in prenatal hormonal transfers. However, that conclusion seems premature: the
observations are consistent with the possibility of bothhormonal factors and the presence of an older brother
having an effect (especially if the latter influences the former). This study
also found no correlation between experiencing same-sex attraction and having
multiple older brothers, which had been reported in some earlier studies.[41]
Finally, Bearman and Brückner did not find evidence of significant
genetic influence on sexual attraction. Significant influence would require
that identical twins have significantly higher concordance rates for same-sex
attraction than fraternal twins or non-twin siblings. But in the study, the
rates were statistically similar: identical twins were 6.7% concordant,
dizygotic pairs 7.2% concordant, and full siblings 5.5% concordant. The authors
concluded that “it is more likely that any genetic influence, if present, can
only be expressed in specific and circumscribed social structures.”[42] Based on their data, they suggested
the one observed social structure that might enable this genetic expression is
the more limited “gender socialization associated with firstborn OS
[opposite-sex] twin pairs.”[43] Thus, they inferred that their results
“support the hypothesis that less gendered socialization in early childhood and
preadolescence shapes subsequent same-sex romantic preferences.”[44] While the findings here are
suggestive, further research is needed to confirm this hypothesis. The authors
also argued that the higher concordance rates for same-sex attraction reported
in previous studies may be unreliable due to methodological problems such as
non-representative samples and small sample sizes. (It should be noted,
however, that these remarks were published prior to the study by Långström and
colleagues discussed above, which uses a study design that does not appear to
have these limitations.)
To reconcile the
somewhat mixed data on heritability, we could hypothesize that attraction to
the same sex may have a stronger heritable component as people age — that is,
when researchers attempt to measure sexual orientation later in life (as in the
2010 study by Långström and colleagues) than when measured earlier in life.
Heritability estimates can change depending on the age at which a trait is
measured because changes in the environmental factors that might influence
variation in the trait may vary for individuals at different ages, and because
genetically influenced traits may become more fixed at a later stage in an
individual’s development (height, for instance, becomes fixed in early
adulthood). This hypothesis is also suggested by findings, discussed below,
that same-sex attraction may be more fluid in adolescence than in later stages
of adulthood.
In contrast to the studies just summarized, psychiatrist Kenneth
S. Kendler and colleagues conducted a large twin study using a probability
sample of 794 twin pairs and 1,380 non-twin siblings.[45] Based on concordance rates for sexual
orientation (defined in this study as self-identification based on attraction),
the authors state that their results “suggest that genetic factors may provide
an important influence on sexual orientation.”[46] The study does not, however, appear to
be sufficiently powerful to draw strong conclusions about the degree of genetic
influence on sexuality: only 19 of 324 identical twin pairs had any
non-heterosexual member, with 6 of the 19 pairs concordant; 15 of 240 same-sex
fraternal twin pairs had any non-heterosexual member, with 2 of the 15 pairs
concordant. Because only 8 twin pairs were concordant for non-heterosexuality,
the study’s ability to draw substantively significant comparisons between
identical and fraternal twins (or between twins and non-twin siblings) is
limited.
Overall, these
studies suggest that (depending on how homosexuality is defined) in anywhere
from 6% to 32% of cases, both members of an identical twin pair would be
homosexual if at least one member is. Since some twin studies found higher
concordance rates in identical twins than in fraternal twins or non-twin
siblings, there may be genetic influences on sexual desire and behavioral
preferences. One needs to bear in mind that identical twins typically have even
more similar environments — early attachment experiences, peer relationships,
and the like — than fraternal twins or non-twin siblings. Because of their
similar appearances and temperaments, for example, identical twins may be more
likely than fraternal twins or other siblings to be treated similarly. So some
of the higher concordance rates may be attributable to environmental factors
rather than genetic factors. In any case, if genes do play a role in
predisposing people toward certain sexual desires or behaviors, these studies
make clear that genetic influences cannot be the whole story.
Summarizing the
studies of twins, we can say that there is no reliable scientific evidence that
sexual orientation is determined by a person’s genes. But there is evidence
that genes play a role in influencing sexual orientation. So the question “Are
gay people born that way?” requires clarification. There is virtually no
evidence that anyone, gay or straight, is “born that way” if that means their
sexual orientation was genetically determined. But there is some evidence from
the twin studies that certain genetic profiles probably increase the likelihood
the person later identifies as gay or engages in same-sex sexual behavior.
Future twin studies
on the heritability of sexual orientation should include analyses of larger
samples or meta-analyses or other systematic reviews to overcome the limited
sample size and statistical power of some of the existing studies, and analyses
of heritability rates across different dimensions of sexuality (such as attraction,
behavior, and identity) to overcome the imprecisions of the ambiguous concept
of sexual orientation and the limits of studies that look at only one of these
dimensions of sexuality.
In examining the question whether, and perhaps to what extent,
there may be genetic contributions to homosexuality, we have so far looked at
studies that employ methods of classical genetics to estimate the heritability
of a trait like sexual orientation but that do not identify particular genes that
may be associated with the trait.[47] But genetics can also be studied using
what are often called molecular methods that provide estimates of which
particular genetic variations are associated with traits, whether physical or
behavioral.
One early attempt to identify a more specific genetic basis for
homosexuality was a 1993 study by geneticist Dean Hamer and colleagues of 40
pairs of homosexual brothers.[48] By examining the family history of
homosexuality for these individuals, they identified a possible linkage between
homosexuality in males and genetic markers on the Xq28 region of the X
chromosome. Attempts to replicate this influential study’s results have had
mixed results: George Rice and colleagues attempted and failed to replicate
Hamer’s findings,[49] though in 2015 Alan R. Sanders and
colleagues were able to replicate Hamer’s original findings using a larger
population size of 409 male twin pairs of homosexual brothers, and to find
additional genetic linkage sites.[50] (Since the effect was small, however,
the genetic marker would not be a good predictor of sexual orientation.)
Genetic linkage studies like the ones discussed above are able to
identify particular regions of chromosomes that may be associated with a trait
by looking at patterns of inheritance. Today, one of the chief methods for
inferring which genetic variants are associated with a trait is the genome-wide
association study, which uses DNA sequencing technologies to identify
particular differences in DNA that may be associated with a trait. Scientists
examine millions of genetic variants in large numbers of individuals who have a
particular trait, as well as individuals who do not have the trait, and compare
the frequency of genetic variants among those who do and do not have the trait.
Specific genetic variants that occur more frequently among those who have than
those who do not have the trait are inferred to have some association with that
trait. Genome-wide association studies have become popular in recent years, yet
few such scientific studies have found significant associations of genetic
variants with sexual orientation. The largest attempt to identify genetic
variants associated with homosexuality, a study of over 23,000 individuals from
the 23andMe database presented at the American Society of Human Genetics annual
meeting in 2012, found no linkages reaching genome-wide significance for
same-sex sexual identity for males or females.[51]
So, again, the
evidence for a genetic basis for homosexuality is inconsistent and
inconclusive, which suggests that, though genetic factors explain some of the
variation in sexual orientation, the genetic contribution to this trait is not
likely to be strong and even less likely to be decisive.
As is often true of
human behavioral tendencies, there may be genetic contributions to the tendency
toward homosexual inclinations or behaviors. Phenotypic expression of genes is
usually influenced by environmental factors — different environments may lead
to different phenotypes even for the same genes. So even if there are genetic
factors that contribute to homosexuality, an individual’s sexual attractions or
preferences may also be influenced by a number of environmental factors, such
as social stressors, including emotional, physical, or sexual abuse. Looking to
developmental, environmental, experiential, social, or volitional factors will
be necessary to arrive at a fuller picture of how sexual interests, attractions,
and desires develop.
Lay readers might note at this point that even at the purely
biological level of genetics, the shopworn “nature vs. nurture” debates
regarding human psychology have been abandoned by scientists, who recognize
that no credible hypothesis can be offered for any particular traits that would
be determined either purely by genetics or the environment. The growing field
of epigenetics, for example, demonstrates that even for relatively simple
traits, gene expression itself can be influenced by innumerable other external
factors that can shape the functioning of genes.[52] This is even more relevant when it
comes to the relationship between genes and complex traits like sexual
attraction, drives, and behaviors.
These gene-environment relationships are complex and
multidimensional. Non-genetic developmental factors and environmental
experiences may be sculpted, in part, by genetic factors working in subtle
ways. For example, social geneticists have documented the indirect role of
genes in peer-aligned behaviors, such that an individual’s physical appearance
could influence whether a particular social group will include or exclude that
individual.[53]
Contemporary geneticists know that genes can influence a person’s
range of interests and motivations, therefore indirectly affecting behavior.
While genes may in this way incline a person to certain behaviors, compelling
behavior directly, independently of a wide range of other factors, seems less
plausible. They may influence behavior in more subtle ways, depending on
external environmental stimuli (for instance, peer pressure, suggestion, and
behavioral rewards) in conjunction with psychological factors and physical
makeup. Dean Hamer, whose work on the possible role of genetics in homosexuality
was examined above, explained some of the limitations of behavioral genetics in
a 2002 article in Science:
“The real culprit [of lack of progress in behavioral genetics] is the
assumption that the rich complexity of human thought and emotion can be reduced
to a simple, linear relation between individual genes and behaviors.... This
oversimplified model, which underlies most current research in behavior
genetics, ignores the critical importance of the brain, the environment, and
gene expression networks.”[54]
The genetic
influences affecting any complex human behavior — whether sexual behaviors, or
interpersonal interactions — depend in part on individuals’ life experiences as
they mature. Genes constitute only one of the many key influences on behavior
in addition to environmental influences, personal choices, and interpersonal
experiences. The weight of evidence to date strongly suggests that the
contribution of genetic factors is modest. We can say with confidence that
genes are not the sole, essential cause of sexual orientation; there is
evidence that genes play a modest role in contributing to the development of
sexual attractions and behaviors but little evidence to support a simplistic
“born that way” narrative concerning the nature of sexual orientation.
Another area of research relevant to the hypothesis that people are
born with dispositions toward different sexual orientations involves prenatal
hormonal influences on physical development and subsequent male- or
female-typical behaviors in early childhood. For ethical and practical reasons,
the experimental work in this field is carried out in non-human mammals, which
limits how this research can be generalized to human cases. However, children
who are born with disorders of sexual development (DSD) serve as a population
in which to examine the influence of genetic and hormonal abnormalities on the
subsequent development of non-typical sexual identity and sexual orientation.
Hormones responsible for sexual differentiation are generally
thought to exert on the developing fetus either organizational effects — which produce permanent
changes in the wiring and sensitivity of the brain, and thus are considered
largely irreversible — or activating effects, which occur later in an
individual’s life (at puberty, and into adulthood).[55] Organizational hormones may prime the
fetal systems (including the brain) structurally, and set the stage for
sensitivity to hormones presenting at puberty and beyond, when the hormone will
then “activate” systems which were “organized” prenatally.
Periods of peak response to the hormonal environment are thought
to occur during gestation. For example, testosterone is thought to influence
the male fetus maximally between weeks 8 and 24, and then again at birth, until
about three months of age.[56] Estrogens are provided throughout
gestation by the placenta and the mother’s blood system.[57] Studies in animals reveal there may
even be multiple periods of sensitivity for a variety of hormones, that the
presence of one hormone may influence the action of another hormone, and the
sensitivity of the receptors for these hormones can influence their actions.[58] Sexual differentiation, alone, is a
highly complex system.
Specific hormones of interest in this area of research are
testosterone, dihydrotestosterone (a metabolite of testosterone, and more
potent than testosterone), estradiol (which can be metabolized into testosterone),
progesterone, and cortisol. The generally accepted pathways of normal hormonal
influence of development in utero are as follows. The typical pattern of sex
differentiation in human fetuses begins with the differentiation of the sex
organs into testes or ovaries, a process that is largely genetically
controlled. Once these organs have differentiated, they produce specific
hormones that determine development of external genitalia. This window of time
in gestation is when hormones exert their phenotypic and neurological effects.
Testosterone secreted by the testes contributes to the development of male
external genitalia and affects neurological development in males;[59] it is the absence of testosterone in
females which allows for the female pattern of external genitalia to develop.[60] Imbalances of testosterone or
estrogen, as well as their presence or absence at specific critical periods of
gestation, may cause disorders of sexual development. (Genetic or environmental
effects can also lead to disorders of sexual development.)
Stress may also play some role in influencing the way hormones
shape gonadal development, neurodevelopment, and subsequent sex-typical
behaviors in early childhood.[61] Cortisol is the main hormone
associated with stress responses. It may originate from the mother, if she
experiences severe stressors during her pregnancy, or from the fetus under
stress.[62] Elevated levels of cortisol may also
occur from genetic defects.[63] One of the most extensively studied
disorders of sexual development is congenital adrenal hyperplasia (CAH), which
in females can result in genital virilization.[64] Over 90% of cases of CAH result from a
mutation in a gene that codes for an enzyme that helps synthesize cortisol.[65] This results in an overproduction of
cortisol precursors, some of which are converted into androgens (hormones
associated with male sex development).[66] As a result, girls are born with some
degree of virilization of their genitalia, depending on the severity of the
genetic defect.[67] For severe cases of genital
virilization, surgical intervention is sometimes performed to normalize the
genitalia. Hormone therapies are also often administered to mitigate the
effects of excess androgen production.[68] Females with CAH, who as fetuses were
exposed to above-average levels of androgens, are less likely to be exclusively
heterosexual than females without CAH, and females with more severe forms of
CAH are more likely to be non-heterosexual than females with milder forms of
the condition.[69]
Likewise, there are disorders of sexual development in genetic
males affected by androgen insensitivity. In males with androgen insensitivity
syndrome, the testes produce testosterone normally, but the receptors to
testosterone are not functional.[70] The genitalia, at birth, appear to be
female, and the child is usually raised as a female. The individual’s
endogenous testosterone is broken down into estrogen, such that the individual
begins to develop female secondary sex characteristics.[71] It does not become apparent that there
is a problem until puberty, when the individual does not start menses
appropriately.[72] These patients generally prefer to
continue life as females, and their sexual orientation does not differ from
females having an XX genotype.[73] Studies have suggested that they are
just as likely if not more likely to be exclusively interested in male partners
than XX females.[74]
There are other disorders of sexual development affecting some
genetic males (i.e., with an XY genotype) in whom androgen deficiencies are a
direct result of the lack of enzymes either to synthesize dihydrotestosterone
from testosterone or to produce testosterone from its precursor hormone.[75] Individuals with these deficiencies
are born with varied degrees of ambiguous genitalia, and are sometimes raised
as girls. During puberty, however, these individuals often experience physical
virilization, and must then decide whether to live as men or women. Peggy T.
Cohen-Kettenis, a professor of gender development and psychopathology, found
that 39 to 64% of individuals with these deficiencies who are raised as girls
change to live as men in adolescence and early adulthood, and she also reported
that “the degree of external genital masculinization at birth does not seem to
be related to gender role changes in a systematic way.”[76]
The twin studies
reviewed earlier may shed light on the role of maternal hormonal influences,
since both identical and fraternal twins are exposed to similar maternal
hormonal influences in utero. The relatively weak concordance rates in the twin
studies suggest that prenatal hormones, like genetic factors, do not play a
strongly determinative role in sexual orientation. Other attempts at finding
significant hormonal influences on sexual development have likewise been mixed,
and the salience of the findings is not yet clear. Since direct studies of
prenatal hormonal influences on sexual development are methodologically
difficult, some studies have tried to develop models whereby differences in
prenatal hormonal exposure can be inferred indirectly — by measuring subtle
morphological changes or by examining hormonal disorders that are present later
during development.
For example, one rough proxy of prenatal testosterone levels used
by researchers is the ratio between the length of the second finger (index
finger) and the fourth finger (ring finger), which is commonly called the “2D:4D
ratio.” Some evidence suggests that the ratio may be influenced by prenatal
exposure to testosterone, such that in males higher levels of exposure to
testosterone cause shorter index fingers relative to the ring finger (or having
a low 2D:4D ratio), and vice versa.[77] According to one hypothesis,
homosexual men may have a higher 2D:4D ratio (closer to the ratio found in
females than in heterosexual males), while another hypothesis suggests the
opposite, that homosexual men may be hypermasculinized by prenatal
testosterone, resulting in a lower ratio than in heterosexual men. For women,
the hypothesis for homosexuality that they have been hypermasculinized (lower
ratio, higher testosterone) has also been proposed. Several studies comparing
this trait in homosexually versus heterosexually identified men and women have
shown mixed results.
A study published in Nature in 2000 found that in a sample of 720
California adults, the right-hand 2D:4D ratio of homosexual women was
significantly more masculine (that is, the ratio was smaller) than that of
heterosexual women and did not differ significantly from that of heterosexual
men.[78]This
study also found no significant difference in mean 2D:4D ratio between
heterosexual and homosexual men. Another study that year, which used a
relatively small sample of homosexual and heterosexual men from the United
Kingdom, reported a lower 2D:4D (that is, more masculine) ratio in homosexual
men.[79] A 2003 study using a London-based
sample also found that homosexual men had a lower 2D:4D ratio than
heterosexuals,[80] while two other studies with samples
from California and Texas showed higher 2D:4D ratios for homosexual men.[81]
A 2003 twin study compared seven female monozygotic twin pairs
discordant for homosexuality (one twin was lesbian) and five female monozygotic
twin pairs concordant for homosexuality (both twins were lesbian).[82] In the twin pairs discordant for
sexual orientation, the individuals identifying as homosexual had significantly
lower 2D:4D ratios than their twins, whereas the concordant twins showed no difference.
The authors interpreted this result as suggesting that “low 2D:4D ratio is a
result of differences in prenatal environment.”[83] Finally, a 2005 study of 2D:4D ratios
in an Austrian sample of 95 homosexual and 79 heterosexual men found that the
2D:4D ratios of heterosexual men were not significantly different from those of
homosexual men.[84] After reviewing the several studies on
this trait, the authors conclude that “more data are essential before we can be
sure whether there is a 2D:4D effect for sexual orientation in men when ethnic
variation is controlled for.”[85]
Much research has
examined the effects of prenatal hormones on behavior and brain structure.
Again, these results come primarily from studies of non-human primates, but the
study of disorders of sexual development has provided helpful insights into the
effects of hormones on sexual development in humans. Since hormonal influences
typically occur during time-sensitive periods of development, when their
effects manifest physically, it is reasonable to assume that organizational
effects of these early, time-linked hormonal patterns are likely to direct
aspects of neural development. Neuroanatomical connectivity and neurochemical
sensitivities may be among such influences.
In 1983, Günter Dörner and colleagues performed a study
investigating whether there is any relationship between maternal stress during
pregnancy and later sexual identity of their children, interviewing two hundred
men about stressful events that may have occurred to their mothers during their
prenatal lives.[86] Many of these events occurred as a
consequence of World War II. Of men who reported that their mothers had
experienced moderately to severely stressful events during pregnancy, 65% were
homosexual, 25% were bisexual, and 10% were heterosexual. (Sexual orientation
was assessed using the Kinsey scale.) However, more recent studies have shown
much smaller or no significant correlations.[87] In a 2002 prospective study on the
relationship between sexual orientation and prenatal stress during the second
and third trimesters, Hines and colleagues found that stress reported by
mothers during pregnancy showed “only a small relationship” to male-typical
behaviors in their daughters at the age of 42 months, “and no relationship at
all” to female-typical behaviors in their sons.[88]
In summary, some
forms of prenatal hormone exposure, particularly CAH in females, are associated
with differences in sexual orientation, while other factors are often important
in determining the physical and psychological effects of those exposures.
Hormonal conditions that contribute to disorders of sex development may
contribute to the development of non-heterosexual orientations in some
individuals, but this does not demonstrate that such factors explain the
development of sexual attractions, desires, and behaviors in the majority of
cases.
There have been several studies examining neurobiological
differences between individuals who identify as heterosexual and those who
identify as homosexual. This work began with neuroscientist Simon LeVay’s 1991
study that reported biological differences in the brains of gay men as compared
to straight men — specifically, a difference in volume in a particular cell
group of the interstitial nuclei of the anterior hypothalamus (INAH3).[89] Later work by psychiatrist William
Byne and colleagues showed more nuanced findings: “In agreement with two prior
studies ... we found INAH3 to be sexually dimorphic, occupying a significantly
greater volume in males than females. In addition, we determined that the sex
difference in volume was attributable to a sex difference in neuronal number
and not in neuronal size or density.”[90] The authors noted that, “Although
there was a trend for INAH3 to occupy a smaller volume in homosexual men than
in heterosexual men, there was no difference in the number of neurons within
the nucleus based on sexual orientation.” They speculated that “postnatal
experience” may account for the differences in volume in this region between
homosexual and heterosexual men, though this would require further research to
confirm.[91] They also noted that the functional
significance of sexual dimorphism in INAH3 is unknown. The authors conclude:
“Based on the results of the present study as well as those of LeVay (1991),
sexual orientation cannot be reliably predicted on the basis of INAH3 volume
alone.”[92] In 2002, psychologist Mitchell S.
Lasco and colleagues published a study examining a different part of the brain
— the anterior commissure — and found that there were no significant
differences in that area based either on sex or sexual orientation.[93]
Other studies have since been conducted to ascertain structural or
functional differences between the brains of heterosexual and homosexual
individuals (using a variety of criteria to define these categories). Findings
from several of these studies are summarized in a 2008 commentary published in
the Proceedings of the
National Academy of Sciences.[94] Research of this kind, however, does
not seem to reveal much of relevance regarding the etiology or biological origins
of sexual orientation. Due to inherent limitations, this research literature is
fairly unremarkable. For example, in one study functional MRI was used to
measure activity changes in the brain when pictures of men and women were shown
to subjects, finding that viewing a female face produced stronger activity in
the thalamus and orbitofrontal cortex of heterosexual men and homosexual women,
whereas in homosexual men and heterosexual women these structures reacted more
strongly to the face of a man.[95] That the brains of heterosexual women
and homosexual men reacted distinctively to the faces of men, whereas the
brains of heterosexual men and homosexual women reacted distinctively to the
faces of women, is a finding that seems rather trivial with respect to
understanding the etiology of homosexual attractions. In a similar vein, one
study reported different responses to pheromones between homosexual and
heterosexual men,[96] and a follow-up study showed a similar
finding in homosexual compared to heterosexual women.[97] Another study showed differences in
cerebral asymmetry and functional connectivity between homosexual and
heterosexual subjects.[98]
While findings of this kind may suggest avenues for future
investigation, they do not move us much closer to an understanding of the
biological or environmental determinants of sexual attractions, interests,
preferences, or behaviors. We will say more about this below. For now, we will
briefly illustrate a few of the inherent limitations in this area of research
with the following hypothetical example. Suppose we were to study the brains of
yoga teachers and compare them to the brains of bodybuilders. If we search long
enough, we will eventually find statistically significant differences in some
area of brain morphology or brain function between these two groups. But this
would not imply that such differences determined the different life
trajectories of the yoga teacher and the bodybuilder. The brain differences
could have been the result, rather than the cause, of distinctive patterns of
behavior or interests.[99] Consider another example. Suppose that
gay men tend to have less body fat than straight men (as indicated by lower
average scores on body mass indices). Even though body mass is, in part,
determined by genetics, we could not claim based on this finding that there is
some innate, genetic cause of both body mass and homosexuality at work. It
could be the case, for instance, that being gay is associated with a diet that
lowers body mass. These examples illustrate one of the common problems
encountered in the popular interpretation of such research: the suggestion that
the neurobiological pattern determines a particular behavioral expression.
With this overview of studies on biological factors that might
influence sexual attraction, preferences, or desires, we can understand the
rather strong conclusion by social psychologist Letitia Anne Peplau and
colleagues in a 1999 review article: “To recap, more than 50 years of research
has failed to demonstrate that biological factors are a major influence in the
development of women’s sexual orientation.... Contrary to popular belief,
scientists have not convincingly demonstrated that biology determines women’s
sexual orientation.”[100] In light of the studies we have
summarized here, this statement could also be made for research on male sexual
orientation, however this concept is defined.
There are some significant built-in limitations to what the kind of
empirical research summarized in the preceding sections can show. Ignoring
these limitations is one of the main reasons the research is routinely
misinterpreted in the public sphere. It may be tempting to assume, as we just
saw with the example of brain structure, that if a particular biological
profile is associated with some behavioral or psychological trait, then that
biological profile causes that trait. This reasoning relies on a
fallacy, and in this section we explain why, using concepts from the field of
epidemiology. While some of these issues are rather technical in detail, we
will try to explain them in a general way that is accessible to the
non-specialist reader.
Suppose for the
sake of illustration that one or more differences in a biological trait are
found between homosexual and heterosexual men. That difference could be a discrete
measure (call this D) such as presence of a genetic marker, or it could be a
continuous measure (call this C) such as the average volume of a particular
part of the brain.
Showing that a risk
factor significantly increases the chances of a particular health outcome or a
behavior might give us a clue to development of that health outcome or that
behavior, but it does not provide evidence of causation. Indeed, it may not
provide evidence of anything but the weakest of correlations. The inference is
sometimes made that if it can be shown that gay men and straight men differ
significantly in the probability that D is present (whether a gene, a hormonal
factor, or something else), no matter how low that probability, then this
finding suggests that being gay has a biological basis. But this inference is
unwarranted. Doubling (or even tripling or quadrupling) the probability of a
relatively rare trait can have little value in terms of predicting who will or
will not identify as gay.
The same would be
true for any continuous variable (C). Showing a significant difference at the
mean or average for a given trait (such as the volume of a particular brain
region) between men who identify as heterosexual and men who identify as
homosexual does not suffice to show that this average difference contributes to
the probability of identifying as heterosexual or homosexual. In addition to
the reasons explained above, a significant difference at the means of two
distributions can be consistent with a great deal of overlap between the
distributions. That is, there may be virtually no separation in terms of
distinguishing between some individual members of each group, and thus the
measure would not provide much predictability for sexual orientation or
preference.
Some of these issues
could, in part, be addressed by additional methodological approaches, such as
the use of a training sample or cross-validation procedures. A training sample
is a small sample used to develop a model (or hypothesis); this model is then
tested on a larger independent sample. This method avoids testing a hypothesis
on the same data used to develop the hypothesis. Cross-validation includes
procedures used to examine whether a statistically significant effect is really
there or just due to chance. If one wants to show the result did not occur by
chance (and if the sample is large), one can run the same tests on a random
split of the relevant sample. After finding a difference in the prevalence of
trait D or C between a gay sample and a straight sample, researchers could
randomly split the gay sample into two groups and then show that these two
groups do not differ regarding D or C. Suppose one finds five differences out
of 100 comparing gay to straight men in the overall samples, then finds five
differences out of 100 when comparing the split gay samples. This would cast
additional doubt on the initial finding of a difference between the means of
gay and straight individuals.
Whereas the preceding discussion considered the part that
biological factors might play in the development of sexual orientation, this
section will summarize evidence that a particular environmental factor —
childhood sexual abuse — is reported significantly more often among those who
later identify as homosexual. The results presented below raise the question
whether there is an association between sexual abuse, particularly in
childhood, and later expressions of sexual attraction, behavior, or identity.
If so, might child abuse increase the probability of having a non-heterosexual
orientation?
Correlations, at
least, have been found, as we will summarize below. But we should note first
that they might be accounted for by one or more of the following conjectures:
1. Abuse might
contribute to the development of non-heterosexual orientation.
2. Children with
(signs of future) non-heterosexual tendencies might attract abusers, placing
them at elevated risk.
3. Certain factors might contribute to both childhood sexual abuse and
non-heterosexual tendencies (for instance, a dysfunctional family or an
alcoholic parent).
It should be kept
in mind that these three hypotheses are not mutually exclusive; all three, and
perhaps others, might be operative. As we summarize the studies on this issue,
we will try to evaluate each of these hypotheses in light of current scientific
research.
Behavioral and community health professor Mark S. Friedman and
colleagues conducted a 2011 meta-analysis of 37 studies from the United States
and Canada examining sexual abuse, physical abuse, and peer victimization in
heterosexuals as compared to non-heterosexuals.[101] Their results showed that
non-heterosexuals were on average 2.9 times more likely to report having been
abused as children (under 18 years of age). In particular, non-heterosexual
males were 4.9 times likelier — and non-heterosexual females, 1.5 times
likelier — than their heterosexual counterparts to report sexual abuse.
Non-heterosexual adolescents as a whole were 1.3 times likelier to indicate
physical abuse by parents than their heterosexual peers, but gay and lesbian
adolescents were only 0.9 times as likely (bisexuals were 1.4 times as likely).
As for peer victimization, non-heterosexuals were 1.7 times likelier to report
being injured or threatened with a weapon or being attacked.
The authors note that although they hypothesized that the rates of
abuse would decrease as social acceptance of homosexuality rose, “disparities
in prevalence rates of sexual abuse, parental physical abuse, and peer
victimization between sexual minority and sexual nonminority youths did not
change from the 1990s to the first decade of the 2000s.”[102] While these authors cite authorities
who claim that sexual abuse does not “cause individuals to become gay, lesbian,
or bisexual,”[103] their data do not give evidence
against the hypothesis that childhood sexual abuse might affect sexual
orientation. On the other hand, the causal path could be in the opposite
direction or bi-directional. The evidence does not refute or support this
conjecture; the study’s design is not capable of shedding much light on the
question of directionality.
The authors invoke a widely-cited hypothesis to explain the higher
rates of sexual abuse among non-heterosexuals, the hypothesis that “sexual
minority individuals are ... more likely to be targeted for sexual abuse, as
youths who are perceived to be gay, lesbian, or bisexual are more likely to be
bullied by their peers.”[104] The two conjectures — that abuse is a
cause and that it is a result of non-heterosexual tendencies — are not mutually
exclusive: abuse may be a causal factor in the development of non-heterosexual
attractions and desires, and at the same time non-heterosexual attractions,
desires, and behaviors may increase the risk of being targeted for abuse.
Community health sciences professor Emily Faith Rothman and
colleagues conducted a 2011 systematic review of the research investigating the
prevalence of sexual assault against people who identify as gay, lesbian, or
bisexual in the United States.[105] They examined 75 studies (25 of which
used probability sampling) involving a total of 139,635 gay or bisexual (GB)
men and lesbian or bisexual (LB) women, which measured the prevalence of
victimization due to lifetime sexual assault (LSA), childhood sexual assault
(CSA), adult sexual assault (ASA), intimate partner sexual assault (IPSA), and
hate-crime-related sexual assault (HC). Although the study was limited by not
having a heterosexual control group, it showed alarmingly high rates of sexual
assault, including childhood sexual assault, for this population, as summarized
in Table 1.
Table 1. Sexual Assault among Gay/Bisexual Men and
Lesbian/Bisexual Women
|
GB Men (%)
|
LB Women (%)
|
|
CSA: 4.1–59.2 (median 22.7)
|
CSA: 14.9–76.0 (median 34.5)
|
|
ASA: 10.8–44.7 (median 14.7)
|
ASA: 11.3–53.2 (median 23.2)
|
|
LSA: 11.8–54.0 (median 30.4)
|
LSA: 15.6–85.0 (median 43.4)
|
|
IPSA: 9.5–57.0 (median 12.1)
|
IPSA: 3.0–45.0 (median 13.3)
|
|
HC: 3.0–19.8 (median 14.0)
|
HC: 1.0–12.3 (median 5.0)
|
Using a multi-state probability-based sample in a 2013 study,
psychologist Judith Anderson and colleagues compared differences in adverse
childhood experiences — including dysfunctional households; physical, sexual,
or emotional abuse; and parental discord — among self-identified homosexual,
heterosexual, and bisexual adults.[106] They found that bisexuals had
significantly higher proportions than heterosexuals of all adverse childhood
experience factors, and that gays and lesbians had significantly higher
proportions than heterosexuals of all these measures except parental separation
or divorce. Overall, gays and lesbians had nearly 1.7 times, and bisexuals 1.6
times, the heterosexual rate of adverse childhood experiences. The data for
abuse are summarized in Table 2.
Table 2. Adverse Childhood Experiences among Gays/Lesbians,
Bisexuals, and Heterosexuals
Sexual Abuse (%)
|
GLs
|
Bisexuals
|
Heterosexuals
|
|
29.7
|
34.9
|
14.8
|
Emotional Abuse (%)
|
GLs
|
Bisexuals
|
Heterosexuals
|
|
47.9
|
48.4
|
29.6
|
Physical Abuse (%)
|
GLs
|
Bisexuals
|
Heterosexuals
|
|
29.3
|
30.3
|
16.7
|
While this study,
like some others we have discussed, may be limited by recall bias — that is,
inaccuracies introduced by errors of memory — it has the merit of having a
control group of self-identified heterosexuals to compare with self-identified
gay/lesbian and bisexual cohorts. In their discussion of findings, the authors
critique the hypothesis that childhood trauma has a causal relationship to
homosexual preferences. Among their reasons for skepticism, they note that the
vast majority of individuals who suffer childhood trauma do not become gay or
bisexual, and that gender-nonconforming behavior may help explain the elevated
rates of abuse. However, it is plausible from these and related results to
hypothesize that adverse childhood experiences may be a significant — but not a
determinative — factor in developing homosexual preferences. Further studies
are needed to see whether either or both hypotheses have merit.
A 2010 study by professor of social and behavioral sciences Andrea
Roberts and colleagues examined sexual orientation and risk of post-traumatic
stress disorder (PTSD) using data from a national epidemiological face-to-face
survey of nearly 35,000 adults.[107] Individuals were placed into several
categories: heterosexual with no same-sex attraction or partners (reference
group); heterosexual with same-sex attraction but no same-sex partners;
heterosexual with same-sex partners; self-identified gay/lesbian; and
self-identified bisexual. Among those reporting exposure to traumatic events,
gay and lesbian individuals as well as bisexuals had about twice the lifetime
risk of PTSD compared to the heterosexual reference group. Differences were
found in rates of childhood maltreatment and interpersonal violence: gays,
lesbians, bisexuals, and heterosexuals with same-sex partners reported
experiencing worse traumas during childhood and adolescence than the reference
group. The findings are summarized in Table 3.
Table 3. Childhood Exposure to Maltreatment or Interpersonal
Violence (before Age 18)
|
Women
|
Men
|
|
49.2% of lesbians
|
31.5% of gays
|
|
51.2% of bisexuals
|
Approximately 32% of bisexuals[109]
|
|
40.9% of heterosexuals with same-sex partners
|
27.9% of heterosexuals with same-sex partners
|
|
21.2% of heterosexuals
|
19.8% of heterosexuals
|
Similar patterns emerged in a 2012 study by psychologist Brendan
Zietsch and colleagues that primarily focused on the distinct question of
whether common causal factors could explain the association between sexual
orientation — in this study defined as sexual preference — and depression.[108] In a community sample of 9,884 adult
twins, the authors found that non-heterosexuals had significantly elevated
prevalence of lifetime depression (odds ratio for males 2.8; odds ratio for
females 2.7). As the authors point out, the data raised questions about whether
higher rates of depression for non-heterosexuals could be explained, in their
entirety, by the social stress hypothesis (the idea, discussed in depth in Part Two of
this report, that social stress experienced by sexual minorities accounts for
their elevated risks of poor mental health outcomes). Heterosexuals with a
non-heterosexual twin had higher rates of depression (39%) than heterosexual
twin pairs (31%), suggesting that genetic, familial, or other factors may play
a role.
The authors note that “in both males and females, significantly
higher rates of non-heterosexuality were found in participants who experienced
childhood sexual abuse and in those with a risky childhood family environment.”[110] Indeed, 41% of non-heterosexual males
and 42% of non-heterosexual females reported childhood family dysfunction,
compared to 24% and 30% of heterosexual males and females, respectively. And
12% of non-heterosexual males and 24% of non-heterosexual females reported
sexual abuse before the age of 14, compared with 4% and 11% of heterosexual
males and females, respectively. The authors are careful to emphasize that
their findings should not be interpreted as disproving the social stress
hypothesis, but suggest that there may be other factors at work. Their findings
do, however, suggest there could be common etiological factors for depression
and non-heterosexual preferences, as they found that genetic factors account
for 60% of the correlation between sexual orientation and depression.[111]
In a 2001 study, psychologist Marie E. Tomeo and colleagues noted
that the previous literature had consistently found increased rates of reported
childhood molestation in the homosexual population, with somewhere between 10%
and 46% reporting that they had experienced childhood sexual abuse.[112] The authors found that 46% of
homosexual men and 22% of homosexual women reported that they had been molested
by a person of the same gender, as compared with 7% of heterosexual men and 1%
of heterosexual women. Moreover, 68% of homosexual men and 38% of homosexual
women interviewed did not identify as homosexual until after the abuse. The
sample for this study was relatively small, only 267 individuals; also, the
“sexual contact” measure of abuse in the survey was somewhat vague, and the
subjects were recruited from participants in gay pride events in California.
But the authors state that “it is most unlikely that all the present findings
apply only to homosexual persons who go to homosexual fairs and volunteer to
participate in questionnaire research.”[113]
In 2010, psychologists Helen Wilson and Cathy S. Widom published a
prospective 30-year follow-up study — one that looked at children who had
experienced abuse or neglect between 1961 and 1971, and then followed up with
those children after 30 years — to ascertain whether physical abuse, sexual
abuse, or neglect in childhood increased the likelihood of same-sex sexual
relationships later in life.[114] An original sample of 908 abused
and/or neglected children was matched with a non-maltreated control group of
667 individuals (matched for age, sex, race or ethnicity, and approximate
socioeconomic status). Homosexuality was operationalized as anyone who had
cohabited with a same-sex romantic partner or had a same-sex sexual partner,
which made up 8% of the sample. Among these 8%, most individuals also reported
having had opposite-sex partners, suggesting high rates of bisexuality or
fluidity in sexual attractions or behaviors. The study found that those who
reported histories of childhood sexual abuse were 2.8 times more likely to
report having had same-sex sexual relationships, though the “relationship
between childhood sexual abuse and same-sex sexual orientation was significant
only for men.”[115] This finding suggested that boys who
are sexually abused may be more likely to establish both heterosexual and
homosexual relationships.
The authors advised
caution in interpreting this result, because the sample size of sexually abused
men was small, but the association remained statistically significant when they
controlled for total lifetime number of sexual partners and for engaging in
prostitution. The study was also limited by a definition of sexual orientation
that was not sensitive to how participants identified themselves. It may have
failed to capture people with same-sex attractions but no same-sex romantic
relationship history. The study had two notable methodological strengths. The
prospective design is better suited for evaluating causal relationships than
the typical retrospective design. Also, the childhood abuse recorded was
documented when it occurred, thus mitigating recall bias.
Having examined the
statistical association between childhood sexual abuse and later homosexuality,
we turn to the question of whether the association suggests causation.
A 2013 analysis by health researcher Andrea Roberts and colleagues
attempted to provide an answer to this question.[116] The authors noted that while studies
show 1.6 to 4 times more reported childhood sexual and physical abuse among gay
and lesbian individuals than among heterosexuals, conventional statistical
methods cannot demonstrate a strong enough statistical relationship to support the
argument of causation. They argued that a sophisticated statistical method
called “instrumental variables,” imported from econometrics and economic
analysis, could increase the level of association.[117] (The method is somewhat similar to the
method of “propensity scores,” which is more sophisticated and more familiar to
public health researchers.) The authors applied the method of instrumental
variables to data collected from a nationally representative sample.
They used three
dichotomous measures of sexual orientation: any vs. no same-sex attraction; any
vs. no lifetime same-sex sexual partners; and lesbian, gay, or bisexual vs.
heterosexual self-identification. As in other studies, the data showed
associations between childhood sexual abuse or maltreatment and all three
dimensions of non-heterosexuality (attraction, partners, identity), with
associations between sexual abuse and sexual identity being the strongest.
The authors’ instrumental variable models suggested that early
sexual abuse increased the predicted rate of same-sex attraction by 2.0
percentage points, same-sex partnering by 1.4 percentage points, and same-sex
identity by 0.7 percentage points. The authors estimated the rate of
homosexuality that might be attributable to sexual abuse “using effect
estimates from conventional models” and found that on conventional effect
estimates, “9% of same-sex attraction, 21% of any lifetime same-sex sexual
partnering, and 23% of homosexual or bisexual identity was due to childhood
sexual abuse.”[118] We should note that these correlations
are cross-sectional: they compare groups of people to groups of people, rather
than model the course of individuals over time. (A study design with a
time-series analysis would give the strongest statistical support to the claim
of causality.) Additionally, these results have been strongly criticized on
methodological grounds for having made unjustified assumptions in the
instrumental variables regression; a commentary by Drew H. Bailey and J.
Michael Bailey claims, “Not only do Roberts et al.’s results fail to provide
support for the idea that childhood maltreatment causes adult homosexuality,
the pattern of differences between males and females is opposite what should be
expected based on better evidence.”[119]
Roberts and colleagues conclude their study with several
conjectures to explain the epidemiological associations. They echo suggestions
made elsewhere that sexual abuse perpetrated by men might cause boys to think
they are gay or make girls averse to sexual contact with men. They also
conjecture that sexual abuse might leave victims feeling stigmatized, which in
turn might make them more likely to act in ways that are socially stigmatized
(as by engaging in same-sex sexual relationships). The authors also point to
the biological effects of maltreatment, citing studies that show that “quality
of parenting” can affect chemical and hormonal receptors in children, and
hypothesizing that this might influence sexuality “through epigenetic changes,
particularly in the stria terminalis and the medial amygdala, brain regions
that regulate social behavior.”[120] They also mention the possibilities
that emotional numbing caused by maltreatment may drive victims to seek out
risky behaviors associated with same-sex sexuality, or that same-sex
attractions and partnering may result from “the drive for intimacy and sex to
repair depressed, stressed, or angry moods,” or from borderline personality
disorder, which is a risk factor in individuals who have been maltreated.[121]
In short, while
this study suggests that sexual abuse may sometimes be a causal contributor to
having a non-heterosexual orientation, more research is needed to elucidate the
biological or psychological mechanisms. Without such research, the idea that
sexual abuse may be a causal factor in sexual orientation remains speculative.
However sexual desires and interests develop, there is a related
issue that scientists debate: whether sexual desires and attractions tend to
remain fixed and unalterable across the lifespan of a person — or are fluid and
subject to change over time but tend to become fixed after a certain age or developmental
period. Advocates of the “born that way” hypothesis, as mentioned earlier,
sometimes argue that a person is not only born with a sexual orientation but
that that orientation is immutable; it is fixed for life.
There is now considerable scientific evidence that sexual desires,
attractions, behaviors, and even identities can, and sometimes do, change over
time. For findings in this area we can turn to the most comprehensive study of
sexuality to date, the 1992 National Health and Social Life Survey conducted by
the National Opinion Research Center at the University of Chicago (NORC).[122] Two important publications have
appeared using data from NORC’s comprehensive survey: The Social Organization of
Sexuality: Sexual Practices in the United States, a large tome of data
intended for the research community, and Sex
in America: A Definitive Survey, a smaller and more accessible book summarizing
the findings for the general public.[123] These books present data from a
reliable probability sample of the American population between ages 18 and 59.
According to data from the NORC survey, the estimated prevalence
of non-heterosexuality, depending on how it was operationalized, and on whether
the subjects were male or female, ranged between roughly 1% and 9%.[124] The NORC studies added scientific
respectability to sexual surveys, and these findings have been largely
replicated in the United States and abroad. For example, the British National
Survey of Sexual Attitudes and Lifestyles (Natsal) is probably the most
reliable source of information on sexual behavior in that country — a study
conducted every ten years since 1990.[125]
The NORC study also suggested ways in which sexual behaviors and
identities can vary significantly under different social and environmental
circumstances. The findings revealed, for example, a sizable difference in
rates of male homosexual behavior among individuals who spent their adolescence
in rural as compared to large metropolitan cities in America, suggesting the
influence of social and cultural environments. Whereas only 1.2% of males who
had spent their adolescence in a rural environment responded that they had had
a male sexual partner in the year of the survey, those who had spent
adolescence living in metropolitan areas were close to four times (4.4%) more
likely to report that they had had such an encounter.[126] From these data one cannot infer
differences between these environments in the prevalence of sexual interests or
attractions, but the data do suggest differences in sexual behaviors. Also of
note is that women who attended college were nine times more likely to identify
as lesbians than women who did not.[127]
Moreover, other population-based surveys suggest that sexual
desire may be fluid for a considerable number of individuals, especially among
adolescents as they mature through the early stages of adult development. In
this regard, opposite-sex attraction and identity seem to be more stable than
same-sex or bisexual attraction and identity. This is suggested by data from
the National Longitudinal Study of Adolescent to Adult Health (the “Add Health”
study discussed earlier). This prospective longitudinal study of a nationally
representative sample of U.S. adolescents starting in grades 7–12 began during
the 1994–1995 school year, and followed the cohort into young adulthood, with
four follow-up interviews (referred to as Waves I, II, III, IV in the
literature).[128] The most recent was in 2007–2008, when
the sample was aged 24–32.
Same-sex or both-sex romantic attractions were quite prevalent in
the study’s first wave, with rates of approximately 7% for the males and 5% for
the females.[129] However, 80% of the adolescent males
who had reported same-sex attractions at Wave I later identi?ed themselves as
exclusively heterosexual as young adults at Wave IV.[130] Similarly, for adolescent males who,
at Wave I, reported romantic attraction to both sexes, over 80% of them
reported no same-sex romantic attraction at Wave III.[131]The
data for the females surveyed were similar but less striking: for adolescent
females who had both-sex attractions at Wave I, more than half reported
exclusive attraction to males at Wave III.[132]
J. Richard Udry, the director of Add Health for Waves I, II, and
III,[133] was among the first to point out the
fluidity and instability of romantic attraction between the first two waves. He
reported that among boys who reported romantic attraction only to boys and never to girls at Wave I, 48% did so during
Wave II; 35% reported no attraction to either sex; 11% reported exclusively
same-sex attraction; and 6% reported attraction to both sexes.[134]
Ritch Savin-Williams and Geoffrey Ream published a 2007 analysis
of the data from Waves I–III of Add Health.[135] Measures used included whether
individuals ever had a romantic attraction for a given sex, sexual behavior,
and sexual identity. (The categories for sexual identity were 100%
heterosexual, mostly heterosexual but somewhat same-sex attracted, bisexual,
mostly homosexual but somewhat attracted to opposite sex, and 100% homosexual.)
While the authors noted the “stability of opposite-sex attraction and behavior”
between Waves I and III, they found a “high proportion of participants with
same- and both-sex attraction and behavior that migrated into opposite-sex
categories between waves.”[136] A much smaller proportion of those in
the heterosexual categories, and a similar proportion of those without
attraction, moved to non-heterosexual categories. The authors summarize: “All
attraction categories other than opposite-sex were associated with a lower
likelihood of stability over time. That is, individuals reporting any same-sex
attractions were more likely to report subsequent shifts in their attractions
than were individuals without any same-sex attractions.”[137]
The authors also note the difficulties these data present for
trying to define sexual orientation and to classify individuals according to
such categories: “the critical consideration is whether having ‘any’ same-sex
sexuality qualifies as nonheterosexuality. How much of a dimension must be
present to tip the scales from one sexual orientation to another was not
resolved with the present data, only that such decisions matter in terms of
prevalence rates.”[138] The authors suggested that researchers
could “forsake the general notion of sexual orientation altogether and assess
only those components relevant for the research question.”[139]
Another prospective study by biostatistician Miles Ott and
colleagues of 10,515 youth (3,980 males; 6,535 females) in 2013 showed findings
on sexual orientation change in adolescents consistent with the findings of the
Add Health data, again suggesting fluidity and plasticity of same-sex
attractions among many adolescents.[140]
A few years after the Add Health data were originally published,
the Archives of Sexual
Behaviorpublished an article by Savin-Williams and Joyner that critiqued
the Add Health data on sexual attraction change.[141] Before outlining their critique,
Savin-Williams and Joyner summarize the key Add Health findings: “in the
approximately 13 years between Waves I and IV, regardless of whether the
measure was identical across waves (romantic attraction) or discrepant in words
but not in theory (romantic attraction and sexual orientation identity),
approximately 80% of adolescent boys and half of adolescent girls who expressed
either partial or exclusive same-sex romantic attraction at Wave I ‘turned’
heterosexual (opposite-sex attraction or exclusively heterosexual identity) as
young adults.”[142] The authors propose three hypotheses
to explain these discrepancies:
(1) gay adolescents going into the closet during their young adult
years; (2) confusion regarding the use and meaning of romantic attraction as a
proxy for sexual orientation; and (3) the existence of mischievous adolescents
who played a ‘jokester’ role by reporting same-sex attraction when none was
present.[143]
Savin-Williams and
Joyner reject the first hypothesis but find support for the second and the
third. With respect to the second hypothesis, they question the use of romantic
attraction to operationalize sexual identity:
To help us assess
whether the construct/measurement issue (romantic attraction versus sexual
orientation identity) was driving results, we compared the two constructs at
Wave IV.... Whereas over 99% of young adults with opposite-sex romantic
attraction identified as heterosexual or mostly heterosexual and 94% of those
with same-sex romantic attraction identified as homosexual or mostly
homosexual, 33% of both-sex attracted men identified as heterosexual (just 6%
of both-sex attracted women identified as heterosexual). These data indicated
that young adult men and women generally understood the meaning of romantic
attraction to the opposite- or same-sex to imply a particular (and consistent)
sexual orientation identity, with one glaring exception — a substantial subset
of young adult men who, despite their stated both-sex romantic attraction,
identified as heterosexual.
Regarding the third hypothesis for explaining the Add Health data,
Savin-Williams and Joyner note that surveys of adolescents sometimes yield
unusual or distorted results due to adolescents who do not respond truthfully.
The Add Health survey, they observe, had a significant number of unusual
responders. For example, several hundred adolescents reported in the Wave I
questionnaire that they had an artificial limb, whereas in later at-home
interviews, only two of those adolescents reported having an artificial limb.[144] Adolescent boys who went from
nonheterosexual in Wave I to heterosexual in Wave IV were significantly less
likely to report having filled out the Wave I questionnaire honestly; these
boys also displayed other significant differences, such as lower grade point
averages. Additionally, like consistently heterosexual boys, boys who were
inconsistent between Waves I and IV were more popular in their school with boys
than girls, whereas consistently nonheterosexual boys were more popular with
girls. These and other data[145] led the authors to conclude that “boys
who emerged from a gay or bisexual adolescence to become a heterosexual young
adulthood were, by-and-large, heterosexual adolescents who were either confused
and did not understand the measure of romantic attraction or jokesters who
decided, for reasons we were not able to detect, to dishonestly report their
sexuality.”[146] However, the authors were not able to
estimate the proportion of inaccurate responders, which would have helped
evaluate the explanatory power of the hypotheses.
Later in 2014, the Archives
of Sexual Behavior published
a critique of the Savin-Williams and Joyner explanation of Add Health data by
psychologist Gu Li and colleagues.[147] Along with criticizing the methodology
of Savin-Williams and Joyner, these authors argued that the data were
consistent with a scenario in which some nonheterosexual adolescents went “back
into the closet” in later years as a possible reaction to social stress. (We
will examine the effects of social stress on mental health in LGBT populations
in Part Two of this report.) They also claimed that “it makes little sense to
use responses to Wave IV sexual identity to validate or invalidate responses to
Waves I or IV romantic attractions when these aspects of sexual orientation may
not align in the first place.”[148] Regarding the jokester hypothesis,
these authors pose this difficulty: “Although some participants might be
‘jokesters,’ and we as researchers should be cautious of problems associated
with self-report surveys whenever analyzing and interpreting data, it is
unclear why the ‘jokesters’ would answer questions about delinquency honestly,
but not questions about their sexual orientation.”[149]
Savin-Williams and Joyner published a response to the critique in
the same issue of the journal.[150]Responding
to the criticism that their comparison of Wave IV self-reported sexual identity
to Wave I self-reported romantic attractions was unsound, Savin-Williams and
Joyner claimed that the results were quite similar if one used attraction as
the Wave IV measure. They also deemed it highly unlikely that a large
proportion of the respondents who were classified as nonheterosexuals in Wave I
and heterosexuals in Wave IV went “back into the closet,” because the
proportion of individuals in adolescence and young adulthood who are “out of
the closet” usually increases over time.[151]
The following year, the Archives
of Sexual Behavior published
another response to Savin-Williams and Joyner by psychologist Sabra Katz-Wise
and colleagues, which argued that Savin-Williams and Joyner’s “approach to
identifying ‘dubious’ sexual minority youth is inherently flawed.”[152] They wrote that “romantic attraction
and sexual orientation identity are two distinct dimensions of sexual
orientation that may not be concordant, even at a single time point.”[153] They also claimed that “even if Add
Health had assessed the same facets of sexual orientation at all waves, it
would still be incorrect to infer ‘dubious’ sexual minorities from changes on
the same dimension of sexual orientation, because these changes may reflect
sexual fluidity.”[154]
Unfortunately, the
Add Health study does not appear to contain the data that would allow an
assessment to determine which, if any, of these interpretations is likely to be
correct. It may well be the case that a combination of factors contributed to
the differences between the Wave I and Wave IV data. For example, there may
have been some adolescents who responded to the Wave I sexual attraction
questions inaccurately, some openly nonheterosexual adolescents who later went
“back into the closet,” and some adolescents who experienced nonheterosexual attractions
before Wave I that largely disappeared by Wave IV. Other prospective study
designs that track specific individuals across adolescent and adult development
may shed further light on these issues.
While ambiguities
in defining and characterizing sexual desire and orientation make changes in
sexual desire difficult to study, data from these large, population-based
national studies of randomly sampled individuals do suggest that all three
dimensions of sexuality — affect, behavior, and identity — may change over time
for some people. It is unclear, and current research does not address, whether
and to what extent factors subject to volitional control — choice of sexual
partners or sexual behaviors, for example — may influence such changes through
conditioning and other mechanisms that are characterized in the behavioral
sciences.
Several researchers have suggested that sexual orientation and
attractions may be especially plastic for women.[155] For example, Lisa Diamond argued in
her 2008 book Sexual Fluidity that “women’s sexuality is
fundamentally more fluid than men’s, permitting greater variability in its
development and expression over the life course,” based on research by her and
many others.[156]
Diamond’s longitudinal five-year interviews of women in sexual
relationships with other women also shed light on the problems with the concept
of sexual orientation. In many cases, the women in her study reported not so
much setting out to form a lesbian sexual relationship but rather experiencing
a gradual growth of affective intimacy with a woman that eventually led to
sexual involvement. Some of these women rejected the labels of “lesbian,”
“straight,” or “bisexual” as being inconsistent with their lived experience.[157] In another study, Diamond calls into
question the utility of the concept of sexual orientation, especially as it
applies to females.[158] She points out that if the neural
basis of parent-child attachment — including attachment to one’s mother — forms
at least part of the basis for romantic attachments in adulthood, then it would
not be surprising for a woman to experience romantic feelings for another woman
without necessarily wanting to be sexually intimate with her. Diamond’s
research indicates that these kinds of relationships form more often than we
typically recognize, especially among women.
Some researchers have also suggested that men’s sexuality is more
fluid than it was previously thought. For example, Diamond presented a 2014
conference paper, based on initial results from a survey of 394 people, entitled
“I Was Wrong! Men Are Pretty Darn Sexually Fluid, Too!”[159] Diamond based this conclusion on a
survey of men and women between the ages of 18 and 35, which asked about their
sexual attractions and self-described identities at different stages of their
lives. The survey found that 35% of self-identified gay men reported
experiencing opposite-sex attractions in the past year, and 10% of
self-identified gay men reported opposite-sex sexual behavior during the same
period. Additionally, nearly as many men transitioned at some time in their
life from gay to bisexual, queer, or unlabeled identity as did men from
bisexual to gay identity.
In a 2012 review article entitled “Can We Change Sexual
Orientation?” published in the Archives
of Sexual Behavior, psychologist Lee Beckstead wrote, “Although their
sexual behavior, identity, and attractions may change throughout their lives,
this may not indicate a change in sexual orientation ... but a change in
awareness and an expansion of sexuality.”[160] It is difficult to know how to
interpret this claim — that sexual behavior, identity, and attractions may
change but that this does not necessarily indicate a change in sexual
orientation. We have already analyzed the inherent difficulties of defining
sexual orientation, but however one chooses to define this construct, it seems
that the definition would somehow be tied to sexual behavior, identity, or
attraction. Perhaps we can take Beckstead’s claim here as one more reason to
consider dispensing with the construct of sexual orientation in the context of
social science research, as it seems that whatever it might represent, it is
only loosely or inconsistently tied to empirically measurable phenomena.
Given the
possibility of changes in sexual desire and attraction, which research suggests
is not uncommon, any attempt to infer a stable, innate, and fixed identity from
a complex and often shifting mélange of inner fantasies, desires, and
attractions — sexual, romantic, aesthetic, or otherwise — is fraught with
difficulties. We can imagine, for example, a sixteen-year-old boy who becomes
infatuated with a young man in his twenties, developing fantasies centered
around the other’s body and build, or perhaps on some of his character traits
or strengths. Perhaps one night at a party the two engage in physical intimacy,
catalyzed by alcohol and by the general mood of the party. This young man then
begins an anguished process of introspection and self-exploration aimed at
finding the answer to the enigmatic question, “Does this mean I’m gay?”
Current research
from the biological, psychological, and social sciences suggests that this
question, at least as it is framed, makes little sense. As far as science can
tell us, there is nothing “there” for this young man to discover — no fact of
nature to uncover or to find buried within himself. What his fantasies, or his
one-time liaison, “really mean” is subject to any number of interpretations:
that he finds the male figure beautiful, that he was lonely and feeling
rejected the night of the party and responded to his peer’s attentions and
affections, that he was intoxicated and influenced by the loud music and strobe
lights, that he does have a deep-seated sexual or romantic attraction to other
men, and so on. Indeed, psychodynamic interpretations of such behaviors citing
unconscious motivational factors and inner conflicts, many of them interesting,
most impossible to prove, can be spun endlessly.
What we can say with more confidence is that this young man had an
experience encompassing complex feelings, or that he engaged in a sexual act
conditioned by multiple complex factors, and that such fantasies, feelings, or
associated behaviors may (or may not) be subject to change as he grows and
develops. Such behaviors could become more habitual with repetition and thus
more stable, or they may extinguish and recur rarely or never. The research on
sexual behaviors, sexual desire, and sexual identity suggests that both
trajectories are real possibilities.
The concept of sexual orientation is unusually ambiguous compared
to other psychological traits. Typically, it refers to at least one of three
things: attractions, behaviors, or identity. Additionally, we have seen that
sexual orientation often refers to several other things as well: belonging to a
certain community, fantasies (as distinct in some respects from attractions),
longings, strivings, felt needs for certain forms of companionship, and so on.
It is important, then, that researchers are clear about which of these domains
are being studied, and that we keep in mind the researchers’ specified
definitions when we interpret their findings.
Furthermore, not
only can the term “sexual orientation” be understood in several different
senses, most of the senses are themselves complex concepts. Attraction, for
example, could refer to arousal patterns, or to romantic feelings, or to
desires for company, or other things; and each of these things can be present
either sporadically and temporarily or pervasively and long-term, either
exclusively or not, either in a deep or shallow way, and so forth. For this
reason, even specifying one of the basic senses of orientation (attraction,
behavior, or identity) is insufficient for doing justice to the richly varied
phenomenon of human sexuality.
In this part we have criticized the common assumption that sexual desires, attractions, or longingsreveal some
innate and fixed feature of our biological or psychological constitution, a
fixed sexualidentity or orientation. Furthermore, we
may have some reasons to doubt the common assumption that in order to live
happy and flourishing lives, we must somehow discover this innate fact about
ourselves that we call sexuality or sexual
orientation, and invariably express it through particular patterns of
sexual behavior or a particular life trajectory. Perhaps we ought instead to
consider what sorts of behaviors — whether in the sexual realm or elsewhere —
tend to be conducive to health and flourishing, and what kinds of behaviors
tend to undermine a healthy and flourishing life.
[*] “Operationalizing”
refers to the way social scientists make a variable measurable. Homosexuality
may be operationalized as the answers that survey respondents give to questions
about their sexual orientation. Or it could be operationalized as answers to
questions about their desires, attractions, and behavior. Operationalizing variables
in ways that will reliably measure the trait or behavior being studied is a
difficult but important part of any social science research.
[1] Alex
Witchel, “Life After ‘Sex,’” The
New York Times Magazine, January 19, 2012,http://www.nytimes.com/2012/01/22/magazine/cynthia-nixon-wit.html.
[2] Brandon
Ambrosino, “I Wasn’t Born This Way. I Choose to Be Gay,” The New Republic, January 28,
2014,https://newrepublic.com/article/116378/macklemores-same-love-sends-wrong-message-about-being-gay.
[3] J.
Michael Bailey et al., “A
Family History Study of Male Sexual Orientation Using Three Independent
Samples,”Behavior Genetics 29,
no. 2 (1999): 79–86, http://dx.doi.org/10.1023/A:1021652204405;
Andrea Camperio-Ciani, Francesca Corna, Claudio Capiluppi, “Evidence for
maternally inherited factors favouring male homosexuality and promoting female
fecundity,” Proceedings of the
Royal Society B 271, no. 1554
(2004): 2217–2221,http://dx.doi.org/10.1098/rspb.2004.2872; Dean
H. Hamer et al., “A
linkage between DNA markers on the X chromosome and male sexual orientation,” Science 261, no. 5119 (1993): 321–327,http://dx.doi.org/10.1126/science.8332896.
[4] Elizabeth
Norton, “Homosexuality May Start in the Womb,” Science, December 11, 2012,http://www.sciencemag.org/news/2012/12/homosexuality-may-start-womb.
[5] Mark
Joseph Stern, “No, Being Gay Is Not a Choice,” Slate, February 4, 2014,http://www.slate.com/blogs/outward/2014/02/04/choose_to_be_gay_no_you_don_t.html.
[6] David
Nimmons, “Sex and the Brain,” Discover,
March 1, 1994,http://discovermagazine.com/1994/mar/sexandthebrain346/.
[7] Leonard
Sax, Why Gender Matters: What
Parents and Teachers Need to Know about the Emerging Science of Sex Differences (New York: Doubleday, 2005), 206.
[8] Benoit
Denizet-Lewis, “The Scientific Quest to Prove Bisexuality Exists,” The New York Times Magazine,
March 20, 2014, http://www.nytimes.com/2014/03/23/magazine/the-scientific-quest-to-prove-bisexuality-exists.html.
[9] Ibid.
[10] Ibid.
[11] Stephen
B. Levine, “Reexploring the Concept of Sexual Desire,” Journal of Sex & Marital
Therapy, 28, no. 1 (2002), 39, http://dx.doi.org/10.1080/009262302317251007.
[12] Ibid.
[13] See
Lori A. Brotto et al.,
“Sexual Desire and Pleasure,” in APA
Handbook of Sexuality and Psychology, Volume 1: Person-based Approaches,
APA (2014): 205–244; Stephen B. Levine, “Reexploring the Concept of Sexual
Desire,” Journal of Sex &
Marital Therapy 28, no. 1
(2002): 39–51, http://dx.doi.org/10.1080/009262302317251007;
Lisa M. Diamond, “What Does Sexual Orientation Orient? A Biobehavioral Model
Distinguishing Romantic Love and Sexual Desire,” Psychological Review 110, no. 1 (2003): 173–192, http://dx.doi.org/10.1037/0033-295X.110.1.173;
Gian C. Gonzaga et al.,
“Romantic Love and Sexual Desire in Close Relationships,” Emotion 6, no. 2 (2006): 163–179, http://dx.doi.org/10.1037/1528-3542.6.2.163.
[14] Alexander
R. Pruss, One Body: An Essay
in Christian Sexual Ethics (Notre
Dame, Ind.: University of Notre Dame Press, 2012), 360.
[15] Neil
A. Campbell and Jane B. Reece, Biology,
Seventh Edition (San Francisco: Pearson Education, 2005), 973.
[16] See,
for instance, Nancy Burley, “The Evolution of Concealed Ovulation,” American Naturalist 114, no. 6 (1979): 835–858, http://dx.doi.org/10.1086/283532.
[17] David
Woodruff Smith, “Phenomenology,” Stanford
Encyclopedia of Philosophy (2013),http://plato.stanford.edu/entries/phenomenology/.
[18] See,
for instance, Abraham Maslow, Motivation
and Personality, Third Edition (New York: Addison-Wesley Educational
Publishers, 1987).
[19] Marc-André
Raffalovich, Uranisme et
unisexualité: étude sur différentes manifestations de l’instinct sexuel (Lyon, France: Storck, 1896).
[20] See,
generally, Brocard Sewell, In
the Dorian Mode: Life of John Gray 1866–1934 (Padstow, Cornwall, U.K.: Tabb House,
1983).
[21] For
more on the Kinsey scale, see “Kinsey’s Heterosexual-Homosexual Rating Scale,”
Kinsey Institute at Indiana University, http://www.kinseyinstitute.org/research/publications/kinsey-scale.php.
[22] Brief
as Amicus Curiae of Daniel N. Robinson in Support
of Petitioners and Supporting Reversal, Hollingsworth
v. Perry, 133 S. Ct. 2652 (2013).
[23] See,
for example, John Bowlby, “The Nature of the Child’s Tie to His Mother,” The International Journal of
Psycho-Analysis 39 (1958):
350–373.
[24] Edward
O. Laumann et al., The Social Organization of
Sexuality: Sexual Practices in the United States (Chicago: University of Chicago Press,
1994).
[25] American
Psychological Association, “Answers to Your Questions for a Better
Understanding of Sexual Orientation & Homosexuality,” 2008, http://www.apa.org/topics/lgbt/orientation.pdf.
[26] Laumann et al., The Social Organization of
Sexuality, 300–301.
[27] Lisa
M. Diamond and Ritch C. Savin-Williams, “Gender and Sexual Identity,” in Handbook of Applied Development
Science, eds. Richard M. Lerner, Francine Jacobs, and Donald Wertlieb
(Thousand Oaks, Calif.: SAGE Publications, 2002), 101. See also A. Elfin Moses
and Robert O. Hawkins, Counseling
Lesbian Women and Gay Men: A Life-Issues Approach(Saint Louis, Mo.: Mosby,
1982).
[28] John.
C. Gonsiorek and James D. Weinrich, “The Definition and Scope of Sexual
Orientation,” in Homosexuality:
Research Implications for Public Policy, eds. John. C. Gonsiorek and James
D. Weinrich (Newberry Park, Calif.: SAGE Publications, 1991), 8.
[29] Letitia
Anne Peplau et al., “The
Development of Sexual Orientation in Women,” Annual
Review of Sex Research 10,
no. 1 (1999): 83, http://dx.doi.org/10.1080/10532528.1999.10559775.
[30] Lisa
M. Diamond, “New Paradigms for Research on Heterosexual and Sexual-Minority
Development,” Journal of
Clinical Child & Adolescent Psychology 32, no. 4 (2003): 492.
[31] Franz
J. Kallmann, “Comparative Twin Study on the Genetic Aspects of Male
Homosexuality,” Journal of
Nervous and Mental Disease 115,
no. 4 (1952): 283–298, http://dx.doi.org/10.1097/00005053-195201000-00025.
[32] Edward
Stein, The Mismeasure of
Desire: The Science, Theory, and Ethics of Sexual Orientation (New York: Oxford University Press,
1999), 145.
[33] J.
Michael Bailey, Michael P. Dunne, and Nicholas G. Martin, “Genetic and
environmental influences on sexual orientation and its correlates in an
Australian twin sample,” Journal
of Personality and Social Psychology 78,
no. 3 (2000): 524–536, http://dx.doi.org/10.1037/0022-3514.78.3.524.
[34] Bailey
and colleagues calculated these concordance rates using a “strict” criterion
for determining non-heterosexuality, which was a Kinsey score of 2 or greater.
They also calculated concordance rates using a “lenient” criterion, a Kinsey
score of 1 or greater. The concordance rates for this lenient criterion were
38% for men and 30% for women in identical twins, compared to 6% for men and
30% for women in fraternal twins. The differences between the identical and
fraternal concordance rates using the lenient criterion were statistically
significant for men but not for women.
[35] Bailey,
Dunne, and Martin, “Genetic and environmental influences on sexual orientation
and its correlates in an Australian twin sample,” 534.
[36] These
examples are drawn from Ned Block, “How heritability misleads about race,” Cognition 56, no. 2 (1995): 103–104, http://dx.doi.org/10.1016/0010-0277(95)00678-R.
[37] Niklas
Långström et al., “Genetic
and Environmental Effects on Same-sex Sexual Behavior: A Population Study of
Twins in Sweden,” Archives of
Sexual Behavior 39, no. 1
(2010): 75–80, http://dx.doi.org/10.1007/s10508-008-9386-1.
[38] Ibid., 79.
[39] Peter
S. Bearman and Hannah Brückner, “Opposite-Sex Twins and Adolescent Same-Sex
Attraction,” American Journal
of Sociology 107, no. 5
(2002): 1179–1205, http://dx.doi.org/10.1086/341906.
[40] Ibid., 1199.
[41] See,
for example, Ray Blanchard and Anthony F. Bogaert, “Homosexuality in men and
number of older brothers,”American Journal of Psychiatry 153, no. 1 (1996): 27–31, http://dx.doi.org/10.1176/ajp.153.1.27.
[42] Peter
S. Bearman and Hannah Brückner, 1198.
[43] Ibid., 1198.
[44] Ibid., 1179.
[45] Kenneth
S. Kendler et al., “Sexual
Orientation in a U.S. National Sample of Twin and Nontwin Sibling Pairs,”American
Journal of Psychiatry 157,
no. 11 (2000): 1843–1846, http://dx.doi.org/10.1176/appi.ajp.157.11.1843.
[46] Ibid., 1845.
[47] Quantitative
genetic studies, including twin studies, rely on an abstract model based on
many assumptions, rather than on the measurement of correlations between genes
and phenotypes. This abstract model is used to infer the presence of a genetic
contribution to a trait by means of correlation among relatives. Environmental effects
can be controlled in experiments with laboratory animals, but in humans this is
not possible, so it is likely that the best that can be done is to study
identical twins raised apart. But it should be noted that even these studies
can be somewhat misinterpreted because identical twins adopted separately tend
to be adopted into similar socioeconomic environments. The twin studies on
homosexuality do not include any separated twin studies, and the study designs
report few effective controls for environmental effects (for instance,
identical twins likely share a common rearing environment to a greater extent
than ordinary siblings or even fraternal twins).
[48] Dean
H. Hamer et al., “A
linkage between DNA markers on the X chromosome and male sexual orientation,”Science 261, no. 5119 (1993): 321–327, http://dx.doi.org/10.1126/science.8332896.
[49] George
Rice et al., “Male
Homosexuality: Absence of Linkage to Microsatellite Markers at Xq28,” Science 284, no. 5414 (1999): 665–667, http://dx.doi.org/10.1126/science.284.5414.665.
[50] Alan
R. Sanders et al.,
“Genome-wide scan demonstrates significant linkage for male sexual
orientation,”Psychological Medicine 45,
no. 07 (2015): 1379–1388, http://dx.doi.org/10.1017/S0033291714002451.
[51] E.M.
Drabant et al.,
“Genome-Wide Association Study of Sexual Orientation in a Large, Web-based
Cohort,” 23andMe, Inc., Mountain View, Calif. (2012), http://blog.23andme.com/wp-content/uploads/2012/11/Drabant-Poster-v7.pdf.
[52] Richard
C. Francis, Epigenetics: How
Environment Shapes Our Genes (New
York: W. W. Norton & Company, 2012).
[53] See,
for example, Richard P. Ebstein et
al., “Genetics of Human Social Behavior,” Neuron 65, no. 6 (2010): 831–844,http://dx.doi.org/10.1016/j.neuron.2010.02.020.
[54] Dean
Hamer, “Rethinking Behavior Genetics,” Science 298, no. 5591 (2002): 71,http://dx.doi.org/10.1126/science.1077582.
[55] For
an overview of the distinction between the organizational and activating
effects of hormones and its importance in the field of endocrinology, see
Arthur P. Arnold, “The organizational-activational hypothesis as the foundation
for a unified theory of sexual differentiation of all mammalian tissues,” Hormones and Behavior 55, no. 5 (2009): 570–578, http://dx.doi.org/10.1016/j.yhbeh.2009.03.011.
[56] Melissa
Hines, “Prenatal endocrine influences on sexual orientation and on sexually
differentiated childhood behavior,” Frontiers
in Neuroendocrinology 32, no.
2 (2011): 170–182, http://dx.doi.org/10.1016/j.yfrne.2011.02.006.
[57] Eugene
D. Albrecht and Gerald J. Pepe, “Estrogen regulation of placental angiogenesis
and fetal ovarian development during primate pregnancy,” The International Journal of
Developmental Biology 54, no.
2–3 (2010): 397–408, http://dx.doi.org/10.1387/ijdb.082758ea.
[58] Sheri
A. Berenbaum, “How Hormones Affect Behavioral and Neural Development:
Introduction to the Special Issue on ‘Gonadal Hormones and Sex Differences in
Behavior,’” Developmental
Neuropsychology 14 (1998):
175–196,http://dx.doi.org/10.1080/87565649809540708.
[59] Jean
D. Wilson, Fredrick W. George, and James E. Griffin, “The Hormonal Control of
Sexual Development,” Science211
(1981): 1278–1284, http://dx.doi.org/10.1126/science.7010602.
[60] Ibid.
[61] See,
for example, Celina C.C. Cohen-Bendahan, Cornelieke van de Beek, and Sheri A.
Berenbaum, “Prenatal sex hormone effects on child and adult sex-typed behavior:
methods and findings,” Neuroscience
& Biobehavioral Reviews29, no. 2 (2005): 353–384, http://dx.doi.org/10.1016/j.neubiorev.2004.11.004;
Marta Weinstock, “The potential influence of maternal stress hormones on
development and mental health of the offspring,” Brain, Behavior, and Immunity 19, no. 4 (2005): 296–308, http://dx.doi.org/10.1016/j.bbi.2004.09.006;
Marta Weinstock, “Gender Differences in the Effects of Prenatal Stress on Brain
Development and Behaviour,” Neurochemical
Research 32, no. 10 (2007):
1730–1740,http://dx.doi.org/10.1007/s11064-007-9339-4.
[62] Vivette
Glover, T.G. O’Connor, and Kieran O’Donnell, “Prenatal stress and the
programming of the HPA axis,”Neuroscience & Biobehavioral Reviews 35, no. 1 (2010): 17–22, http://dx.doi.org/10.1016/j.neubiorev.2009.11.008.
[63] See,
for example, Felix Beuschlein et
al., “Constitutive Activation of PKA Catalytic Subunit in Adrenal Cushing’s
Syndrome,” New England Journal
of Medicine 370, no. 11
(2014): 1019–1028, http://dx.doi.org/10.1056/NEJMoa1310359.
[64] Phyllis
W. Speiser, and Perrin C. White, “Congenital Adrenal Hyperplasia,” New England Journal of Medicine 349, no. 8 (2003): 776–788, http://dx.doi.org/10.1056/NEJMra021561.
[65] Ibid., 776.
[66] Ibid.
[67] Ibid., 778.
[68] Phyllis
W. Speiser et al.,
“Congenital Adrenal Hyperplasia Due to Steroid 21-Hydroxylase Deficiency: An
Endocrine Society Clinical Practice Guideline,” The Journal of Clinical Endocrinology
and Metabolism 95, no. 9 (2009): 4133–4160,http://dx.doi.org/10.1210/jc.2009-2631.
[69] Melissa
Hines, “Prenatal endocrine influences on sexual orientation and on sexually
differentiated childhood behavior,” 173–174.
[70] Ieuan
A. Hughes et al.,
“Androgen insensitivity syndrome,” The
Lancet 380, no. 9851 (2012):
1419–1428,http://dx.doi.org/10.1016/S0140-6736(12)60071-3.
[71] Ibid., 1420.
[72] Ibid., 1419.
[73] Melissa
S. Hines, Faisal Ahmed, and Ieuan A. Hughes, “Psychological Outcomes and
Gender-Related Development in Complete Androgen Insensitivity Syndrome,” Archives of Sexual Behavior 32, no. 2 (2003): 93–101,http://dx.doi.org/10.1023/A:1022492106974.
[74] See,
for example, Claude J. Migeon Wisniewski et
al., “Complete Androgen Insensitivity Syndrome: Long-Term Medical,
Surgical, and Psychosexual Outcome,” The
Journal of Clinical Endocrinology & Metabolism 85, no. 8 (2000): 2664–2669, http://dx.doi.org/10.1210/jcem.85.8.6742.
[75] Peggy
T. Cohen-Kettenis, “Gender Change in 46,XY Persons with 5α-Reductase-2
Deficiency and 17β-Hydroxysteroid Dehydrogenase-3 Deficiency,” Archives of Sexual Behavior 34, no. 4 (2005): 399–410, http://dx.doi.org/10.1007/s10508-005-4339-4.
[76] Ibid., 399.
[77] See,
for example, Johannes Hönekopp et
al., “Second to fourth digit length ratio (2D:4D) and adult sex hormone
levels: New data and a meta-analytic review,” Psychoneuroendocrinology 32, no. 4 (2007): 313–321,http://dx.doi.org/10.1016/j.psyneuen.2007.01.007.
[78] Terrance
J. Williams et al., “Finger-length ratios and sexual
orientation,” Nature 404, no. 6777 (2000): 455–456,http://dx.doi.org/10.1038/35006555.
[79] S.J.
Robinson and John T. Manning, “The ratio of 2nd to 4th digit length and male
homosexuality,” Evolution and
Human Behavior 21, no. 5
(2000): 333–345, http://dx.doi.org/10.1016/S1090-5138(00)00052-0.
[80] Qazi
Rahman and Glenn D. Wilson, “Sexual orientation and the 2nd to 4th finger
length ratio: evidence for organising effects of sex hormones or developmental
instability?,” Psychoneuroendocrinology 28, no. 3 (2003): 288–303,http://dx.doi.org/10.1016/S0306-4530(02)00022-7.
[81] Richard
A. Lippa, “Are 2D:4D Finger-Length Ratios Related to Sexual Orientation? Yes
for Men, No for Women,”Journal of Personality and Social Psychology 85, no. 1 (2003): 179–188, http://dx.doi.org/10.1037/0022-3514.85.1.179;
Dennis McFadden and Erin Shubel, “Relative Lengths of Fingers and Toes in Human
Males and Females,” Hormones
and Behavior 42, no. 4
(2002): 492–500, http://dx.doi.org/10.1006/hbeh.2002.1833.
[82] Lynn
S. Hall and Craig T. Love, “Finger-Length Ratios in Female Monozygotic Twins
Discordant for Sexual Orientation,” Archives
of Sexual Behavior 32, no. 1
(2003): 23–28, http://dx.doi.org/10.1023/A:1021837211630.
[83] Ibid., 23.
[84] Martin
Voracek, John T. Manning, and Ivo Ponocny, “Digit ratio (2D:4D) in homosexual
and heterosexual men from Austria,” Archives
of Sexual Behavior 34, no. 3
(2005): 335–340, http://dx.doi.org/10.1007/s10508-005-3122-x.
[85] Ibid., 339.
[86] Günter
Dörner et al., “Stressful
Events in Prenatal Life of Bi- and Homosexual Men,” Experimental and Clinical
Endocrinology 81, no. 1 (1983):
83–87, http://dx.doi.org/10.1055/s-0029-1210210.
[87] See,
for example, Lee Ellis et al.,
“Sexual orientation of human offspring may be altered by severe maternal stress
during pregnancy,” Journal of
Sex Research 25, no. 2
(1988): 152–157,http://dx.doi.org/10.1080/00224498809551449;
J. Michael Bailey, Lee Willerman, and Carlton Parks, “A Test of the Maternal
Stress Theory of Human Male Homosexuality,” Archives
of Sexual Behavior 20, no. 3
(1991): 277–293,http://dx.doi.org/10.1007/BF01541847; Lee
Ellis and Shirley Cole-Harding, “The effects of prenatal stress, and of
prenatal alcohol and nicotine exposure, on human sexual orientation,” Physiology & Behavior 74, no. 1 (2001): 213–226,http://dx.doi.org/10.1016/S0031-9384(01)00564-9.
[88] Melissa
Hines et al., “Prenatal
Stress and Gender Role Behavior in Girls and Boys: A Longitudinal, Population
Study,” Hormones and Behavior 42, no. 2 (2002): 126–134, http://dx.doi.org/10.1006/hbeh.2002.1814.
[89] Simon
LeVay, “A Difference in Hypothalamic Structure between Heterosexual and
Homosexual Men,” Science 253, no. 5023 (1991): 1034–1037, http://dx.doi.org/10.1126/science.1887219.
[90] William
Byne et al., “The Interstitial Nuclei of the Human Anterior
Hypothalamus: An Investigation of Variation with Sex, Sexual Orientation, and
HIV Status,” Hormones and
Behavior 40, no. 2 (2001):
87,http://dx.doi.org/10.1006/hbeh.2001.1680.
[91] Ibid., 91.
[92] Ibid.
[93] Mitchell
S. Lasco, et al., “A lack
of dimorphism of sex or sexual orientation in the human anterior commissure,”Brain
Research 936, no. 1 (2002):
95–98, http://dx.doi.org/10.1016/S0006-8993(02)02590-8.
[94] Dick
F. Swaab, “Sexual orientation and its basis in brain structure and function,” Proceedings of the National Academy
of Sciences 105, no. 30
(2008): 10273–10274, http://dx.doi.org/10.1073/pnas.0805542105.
[95] Felicitas
Kranz and Alumit Ishai, “Face Perception Is Modulated by Sexual Preference,” Current Biology 16, no. 1 (2006): 63–68, http://dx.doi.org/10.1016/j.cub.2005.10.070.
[96] Ivanka
Savic, Hans Berglund, and Per Lindström, “Brain response to putative pheromones
in homosexual men,”Proceedings of the National Academy of Sciences 102, no. 20 (2005): 7356–7361,http://dx.doi.org/10.1073/pnas.0407998102.
[97] Hans
Berglund, Per Lindström, and Ivanka Savic, “Brain response to putative
pheromones in lesbian women,”Proceedings of the National Academy of Sciences 103, no. 21 (2006): 8269–8274,http://dx.doi.org/10.1073/pnas.0600331103.
[98] Ivanka
Savic and Per Lindström, “PET and MRI show differences in cerebral asymmetry
and functional connectivity between homo- and heterosexual subjects,” Proceedings of the National Academy
of Sciences 105, no. 27
(2008): 9403–9408, http://dx.doi.org/10.1073/pnas.0801566105.
[99] Research
on neuroplasticity shows that while there are critical periods of development
in which the brain changes more rapidly and profoundly (for instance, during
development of language in toddlers), the brain continues to change across the
lifespan in response to behaviors (like practicing juggling or playing a
musical instrument), life experiences, psychotherapy, medications,
psychological trauma, and relationships. For a helpful and generally accessible
overview of the research related to neuroplasticity, see Norman Doidge, The Brain That Changes Itself:
Stories of Personal Triumph from the Frontiers of Brain Science (New York: Penguin, 2007).
[100] Letitia
Anne Peplau et al., “The
Development of Sexual Orientation in Women,” Annual
Review of Sex Research10, no. 1 (1999): 81, http://dx.doi.org/10.1080/10532528.1999.10559775. Also see
J. Michael Bailey, “What is Sexual Orientation and Do Women Have One?” in Contemporary Perspectives on
Lesbian, Gay, and Bisexual Identities, ed. Debra A. Hope (New York:
Springer, 2009), 43–63, http://dx.doi.org/10.1007/978-0-387-09556-1_3.
[101] Mark
S. Friedman et al., “A
Meta-Analysis of Disparities in Childhood Sexual Abuse, Parental Physical
Abuse, and Peer Victimization Among Sexual Minority and Sexual Nonminority
Individuals,” American Journal
of Public Health 101, no. 8
(2011): 1481–1494, http://dx.doi.org/10.2105/AJPH.2009.190009.
[102] Ibid., 1490.
[103] Ibid., 1492.
[104] Ibid.
[105] Emily
F. Rothman, Deinera Exner, and Allyson L. Baughman, “The Prevalence of Sexual
Assault Against People Who Identify as Gay, Lesbian, or Bisexual in the United
States: A Systematic Review,” Trauma,
Violence, & Abuse 12, no.
2 (2011): 55–66, http://dx.doi.org/10.1177/1524838010390707.
[106] Judith
P. Andersen and John Blosnich, “Disparities in Adverse Childhood Experiences
among Sexual Minority and Heterosexual Adults: Results from a Multi-State
Probability-Based Sample,” PLOS
ONE 8, no. 1 (2013): e54691,http://dx.doi.org/10.1371/journal.pone.0054691.
[107] Andrea
L. Roberts et al.,
“Pervasive Trauma Exposure Among US Sexual Orientation Minority Adults and Risk
of Posttraumatic Stress Disorder,” American
Journal of Public Health 100,
no. 12 (2010): 2433–2441,http://dx.doi.org/10.2105/AJPH.2009.168971.
[108] Brendan
P. Zietsch et al., “Do
shared etiological factors contribute to the relationship between sexual
orientation and depression?,” Psychological
Medicine 42, no. 3 (2012):
521–532, http://dx.doi.org/10.1017/S0033291711001577.
[109] The
exact figure is not reported in the text for reasons the authors do not
specify.
[110] Ibid., 526.
[111] Ibid., 527.
[112] Marie
E. Tomeo et al.,
“Comparative Data of Childhood and Adolescence Molestation in Heterosexual and
Homosexual Persons,” Archives
of Sexual Behavior 30, no. 5 (2001): 535–541, http://dx.doi.org/10.1023/A:1010243318426.
[113] Ibid., 541.
[114] Helen
W. Wilson and Cathy Spatz Widom, “Does Physical Abuse, Sexual Abuse, or Neglect
in Childhood Increase the Likelihood of Same-sex Sexual Relationships and
Cohabitation? A Prospective 30-year Follow-up,” Archives of Sexual Behavior 39, no. 1 (2010): 63–74, http://dx.doi.org/10.1007/s10508-008-9449-3.
[115] Ibid., 70.
[116] Andrea
L. Roberts, M. Maria Glymour, and Karestan C. Koenen, “Does Maltreatment in
Childhood Affect Sexual Orientation in Adulthood?,” Archives of Sexual Behavior 42, no. 2 (2013): 161–171, http://dx.doi.org/10.1007/s10508-012-0021-9.
[117] For
those interested in the methodological details: this statistical method uses a
two-step process where “instruments” — in this case, family characteristics
that are known to be related to maltreatment (presence of a stepparent,
parental alcohol abuse, or parental mental illness) — are used as the
“instrumental variables” to predict the risk of maltreatment. In the second
step, the predicted risk of maltreatment is employed as the independent
variable and adult sexual orientation as the dependent variable; coefficients
from this are the instrumental variable estimates. It should also be noted here
that these instrumental variable estimation techniques rely on some important
(and questionable) assumptions, in this case the assumption that the
instruments (the stepparent, the alcohol abuse, the mental illness) do not
affect the child’s sexual orientation measures except through child abuse. But
this assumption is not demonstrated, and therefore may constitute a
foundational limitation of the method. Causation is difficult to support
statistically and continues to beguile research in the social sciences in spite
of efforts to design studies capable of generating stronger associations that
give stronger support to claims of causation.
[118] Roberts,
Glymour, and Koenen, “Does Maltreatment in Childhood Affect Sexual Orientation
in Adulthood?,” 167.
[119] Drew
H. Bailey and J. Michael Bailey, “Poor Instruments Lead to Poor Inferences:
Comment on Roberts, Glymour, and Koenen (2013),” Archives of Sexual Behavior 42, no. 8 (2013): 1649–1652, http://dx.doi.org/10.1007/s10508-013-0101-5.
[120] Roberts,
Glymour, and Koenen, “Does Maltreatment in Childhood Affect Sexual Orientation
in Adulthood?,” 169.
[121] Ibid., 169.
[122] For
information on the study, see “National Health and Social Life Survey,”
Population Research Center of the University of Chicago, http://popcenter.uchicago.edu/data/nhsls.shtml.
[123] Edward
O. Laumann et al., The Social Organization of
Sexuality: Sexual Practices in the United States (Chicago: University of Chicago Press,
1994); Robert T. Michael et
al., Sex in America: A
Definitive Survey (New York:
Warner Books, 1994).
[124] Laumann et al., The Social Organization of
Sexuality, 295.
[125] The
third iteration of Natsal from 2010 found, over an age range from 16 to 74,
that 1.0% of women and 1.5% of men consider themselves gay/lesbian, and 1.4% of
women and 1.0% of men think of themselves as bisexual. See Catherine H. Mercer et al., “Changes in sexual
attitudes and lifestyles in Britain through the life course and over time:
findings from the National Surveys of Sexual Attitudes and Lifestyles
(Natsal),” The Lancet 382, no. 9907 (2013): 1781–1794, http://dx.doi.org/10.1016/S0140-6736(13)62035-8.
Full results of this survey are reported in several articles in the same issue
of The Lancet.
[126] See
Table 8.1 in Laumann et al., The Social Organization of
Sexuality, 304.
[127] This
figure is calculated from Table 8.2 in Laumann et al., The Social Organization of Sexuality,
305.
[128] For
more information on the study design of Add Health, see Kathleen Mullan Harris et al., “Study Design,” The National
Longitudinal Study of Adolescent to Adult Health, http://www.cpc.unc.edu/projects/addhealth/design. Some
studies based on Add Health data use Arabic numerals rather than Roman numerals
to label the waves; when describing or quoting from those studies, we stick
with the Roman numerals.
[129] See
Table 1 in Ritch C. Savin-Williams and Kara Joyner, “The Dubious Assessment of
Gay, Lesbian, and Bisexual Adolescents of Add Health,” Archives of Sexual Behavior 43, no. 3 (2014): 413–422, http://dx.doi.org/10.1007/s10508-013-0219-5.
[130] Ibid., 415.
[131] Ibid.
[132] Ibid.
[133] “Research
Collaborators,” The National Longitudinal Study of Adolescent to Adult Health,http://www.cpc.unc.edu/projects/addhealth/people.
[134] J.
Richard Udry and Kim Chantala, “Risk Factors Differ According to Same-Sex and
Opposite-Sex Interest,” Journal
of Biosocial Science 37, no.
04 (2005): 481–497, http://dx.doi.org/10.1017/S0021932004006765.
[135] Ritch
C. Savin-Williams and Geoffrey L. Ream, “Prevalence and Stability of Sexual
Orientation Components During Adolescence and Young Adulthood,” Archives of Sexual Behavior 36, no. 3 (2007): 385–394,http://dx.doi.org/10.1007/s10508-006-9088-5.
[136] Ibid., 388.
[137] Ibid., 389.
[138] Ibid., 392–393.
[139] Ibid., 393.
[140] Miles
Q. Ott et al., “Repeated Changes in Reported Sexual
Orientation Identity Linked to Substance Use Behaviors in Youth,” Journal of Adolescent Health 52, no. 4 (2013): 465–472,http://dx.doi.org/10.1016/j.jadohealth.2012.08.004.
[141] Savin-Williams
and Joyner, “The Dubious Assessment of Gay, Lesbian, and Bisexual Adolescents
of Add Health.”
[142] Ibid., 416.
[143] Ibid., 414.
[144] For
more analysis of inaccurate responders in the Add Health surveys, see Xitao Fan et al., “An Exploratory Study
about Inaccuracy and Invalidity in Adolescent Self-Report Surveys,” Field Methods 18, no. 3 (2006): 223–244,http://dx.doi.org/10.1177/152822X06289161.
[145] Savin-Williams
and Joyner were also skeptical of the Add Health survey data because the high
proportion of youth reporting same-sex or both-sex attractions (7.3% of boys
and 5.0% of girls) in Wave I was very unusual when compared to similar studies,
and because of the dramatic reduction in reported same-sex attraction a little
over a year later, in Wave II.
[146] Savin-Williams
and Joyner, “The Dubious Assessment of Gay, Lesbian, and Bisexual Adolescents
of Add Health,” 420.
[147] Gu
Li, Sabra L. Katz-Wise, and Jerel P. Calzo, “The Unjustified Doubt of Add
Health Studies on the Health Disparities of Non-Heterosexual Adolescents:
Comment on Savin-Williams and Joyner (2014),” Archives
of Sexual Behavior, 43 no. 6 (2014): 1023–1026, http://dx.doi.org/10.1007/s10508-014-0313-3.
[148] Ibid., 1024.
[149] Ibid., 1025.
[150] Ritch
C. Savin-Williams and Kara Joyner, “The Politicization of Gay Youth Health:
Response to Li, Katz-Wise, and Calzo (2014),” Archives
of Sexual Behavior 43, no. 6
(2014): 1027–1030, http://dx.doi.org/10.1007/s10508-014-0359-2.
[151] See,
for example, Stephen T. Russell et
al., “Being Out at School: The Implications for School Victimization and
Young Adult Adjustment,” American
Journal of Orthopsychiatry 84,
no. 6 (2014): 635–643,http://dx.doi.org/10.1037/ort0000037.
[152] Sabra
L. Katz-Wise et al., “Same
Data, Different Perspectives: What Is at Stake? Response to Savin-Williams and
Joyner (2014a),” Archives of
Sexual Behavior 44, no. 1
(2015): 15, http://dx.doi.org/10.1007/s10508-014-0434-8.
[153] Ibid., 15.
[154] Ibid., 15–16.
[155] For
example, see Bailey, “What is Sexual Orientation and Do Women Have One?,”
43–63; Peplau et al., “The
Development of Sexual Orientation in Women,” 70–99.
[156] Lisa
M. Diamond, Sexual Fluidity (Cambridge, Mass.: Harvard University
Press, 2008), 52.
[157] Lisa
M. Diamond, “Was It a Phase? Young Women’s Relinquishment of Lesbian/Bisexual
Identities Over a 5-Year Period,” Journal
of Personality and Social Psychology 84,
no. 2 (2003): 352–364, http://dx.doi.org/10.1037/0022-3514.84.2.352.
[158] Diamond,
“What Does Sexual Orientation Orient?,” 173–192.
[159] This
conference paper was summarized in Denizet-Lewis, “The Scientific Quest to
Prove Bisexuality Exists.”
[160] A.
Lee Beckstead, “Can We Change Sexual Orientation?,” Archives of Sexual Behavior 41, no. 1 (2012): 128,http://dx.doi.org/10.1007/s10508-012-9922-x.
Lawrence S. Mayer and Paul
R. McHugh, "Part One: Sexual Orientation," Sexuality
and Gender: Findings from the Biological, Psychological, and Social Sciences, The New Atlantis,
Number 50, Fall 2016, pp. 13-58.
