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Nature vs. Nurture: The Biology of Sexuality

MED prof speaks tonight on whether sexual orientation has genetic basis


Richard Pillard says that much about how sexual orientation is determined remains a mystery. “I think some sort of genetic influence seems very likely,” he says, “but beyond that, what really can we say? And the answer is: not a lot.”

Homosexuality was considered a mental illness when Richard Pillard was in medical school. It was the 1950s and the School of Medicine professor of psychiatry was at the University of Rochester. At the time, the American Psychological Association still listed homosexuality as a disorder and psychologists and psychiatrists were trained on ways to treat it.

The first psychological test undertaken to determine whether there was a biological explanation for homosexuality was in 1957. With a grant from the National Institute of Mental Health, Karen Hooker studied the relationship between homosexuality and psychological development and illness. Hooker studied both homosexuals and heterosexuals—matched for age, intelligence, and education level. The subjects were then given three psychological tests: the Rorschach, the Thematic Apperception Test (TAT), and the Make-a-Picture-Story Test (MAPS). Hooker found no major differences in the answers given by the two groups. Because of the similar scores, she concluded that sexuality is not based on environmental factors.

In 1973, based on Hooker’s findings, the American Psychiatric Association removed homosexuality from its Diagnostic and Statistical Manual of Psychological Disorders and in 1975, released a public statement that homosexuality was not a mental disorder.

There have been numerous studies designed to determine whether or not homosexuality has a genetic cause. Among the most notable were a series of studies Pillard and J. Michael Bailey, a professor of psychology at Northwestern University, conducted in the early 1990s that found that homosexuality is largely biologically determined, not environmentally influenced. In their findings, published in the Archives of General Psychiatry, they argued that decades of psychiatric research into social and cultural causes show “small effect size and are causally ambiguous.”

Pillard and Bailey examined identical and fraternal twin brothers—as well as nonrelated brothers who had been adopted—in an effort to see if there was a genetic explanation for homosexuality. They found that if one identical twin was gay, 52 percent of the time the other was also; the figure was 22 percent for fraternal twins, and only 5 percent for nonrelated adopted brothers. Pillard and Bailey’s findings have been debated in the intervening decades.

Pillard is quick to point out that much about how sexual orientation is determined remains a mystery. “It’s really hard to come up with any definite statement about the situation,” he says. “I think some sort of genetic influence seems very likely, but beyond that, what really can we say? And the answer is: not a lot.”

BU Today caught up with Pillard to talk about the lecture he will deliver tonight, titled Born This Way: The Biology of Sexual Orientation. The talk is part of the OUTlook Lecture series, sponsored by the LGBTQ ministry at Marsh Chapel.

BU Today: Has your research found that sexual orientation is biologically determined?
I think so. But nobody knows for sure what causes a person to be either gay or straight. It’s one of the great mysteries of science, at least of biological science.

Can you talk about the twin research you’ve conducted?
What we did was to recruit groups of twins, identical and fraternal twins. And the theory is if a particular trait is genetic, the identical twins would be more alike than the fraternal twins. The results were that they were more alike. The identical twins were far more similar than the fraternal twins.

Is there evidence that life experiences play a role in sexual orientation?
It’s a hard question to answer, because by “experience,” we’re talking about when kids are in the very first years of their life. If you’re going to do research about it, you’re doing research on people 20 or 30 years later, so it’s really hard to look back with certainty on what happened to them in those early years.

But a lot of people have tried, and have said things like, ‘Well, it depends on the fact that your mother was overprotective or that your father was distant or absent.’ You have to reconstruct those theories from events of long ago. And how do you know the mother really was overprotective—you have to depend on what the subject in your study is remembering about his early years. And that could be easily falsified.

Your research suggests that there is often a familial pattern in homosexuality.
Yes. It seems to us that being gay runs in families much more frequently than you would expect by chance alone. And the pattern is hard to specify: that is, in some cases they’re brothers and sisters, in some cases it’s parents and children, or aunts and uncles. So it’s hard to put that into theory given what we know about genes and behavior, which is to say, not a lot.

What made you decide on this research? What was your motivation?
Well, because there are so many gay people in my family, including me. It just seemed like a logical thing to do. At the time that I was searching for a problem, that popped out.

I think that the future of this kind of research belongs to people who are geneticists, people who are expert in gene mapping. These are the sort of bench scientists, where I am more interested in clinical things. I would be very interested if something came of this—that is, when the day comes where genes are mapped, I’d be very interested in that. But, it’s not something that I’m equipped to do.

Do you think that because attitudes are changing and acceptance of the LGBT community is becoming more prevalent, people are more willing to accept the possibility that sexual orientation is determined biologically?
It’s hard to say. Insofar as people look at evidence, it’s clearly biological. The objection to homosexuality comes exclusively from the conservative religious streak, who say, ‘Well, the Bible forbids it, therefore we must be guided by what the Bible says.’ But there’s no other evidence. Lesbians and gay men don’t do worse at their jobs, they are just as good as friends and citizens. As more gay people are out and open about their orientation, the general population realizes, ‘Well, they’re pretty much the same as everybody else.’

When I was in my medical school training in the 1950s, the only places you heard about gay people being were in prison or a mental hospital. So the assumption was, well they’re all quite bizarre. Then in the late 1960s, when civil rights were being granted to people of color and to women and finally to gays, it was realized that they’re like everybody else. I think most people now have friends or acquaintances who are gay. The average college student doesn’t think much about it.

Are you amazed at how far attitudes have changed?
Yes, but it’s taken a long time—50 years is a long time. But it absolutely is changing. Even so, there are people who think that gays shouldn’t be teachers or who are against gay marriage.

Since we don’t really know all the answers, people can have any opinion that crosses their mind. But I think most scientists, most people who are familiar with the science of the area, would say it’s very likely that something genetic is afoot here.

Will you be talking about sexual orientation in any kind of religious context?
I have to say I’m a hard-core atheist. I’m the last person who is qualified in any way to comment on theological matters. But I wonder what college students at BU think. Because I’m on the Medical Campus, I just don’t get the chance to rub shoulders with those on the Charles River Campus. It’ll be interesting to exchange views with them.

Because you’ll be presenting your evidence, and there’s no guesswork.
It’s just the facts, ma’am.

Richard Pillard will discuss Born This Way: The Biology of Sexual Orientation at 7 p.m. Tuesday, November 16, in Stone Science Building, 675 Commonwealth Ave., Room B50. Questions will follow the presentation. At 7 p.m. on November 18, Ellen Perrin, a Tufts University professor of pediatrics, will talk about Where Did We Go Right: Children Raised by Same Sex Couples, at the School of Education, 2 Silber Way, Room 130. Charles Morris, a Boston College professor of communications, will talk about Queer(ing) Public Memory: LGBTQ Pasts and Their Presence at 7 p.m. December 7, in SED 130. The events, sponsored by the LGBTQ Ministry of Marsh Chapel, are free and open to the public. For more information, contact Liz Douglass at lmd@bu.edu.

Kimberly Cornuelle can be reached at kcornuel@bu.edu.


24 Comments on Nature vs. Nurture: The Biology of Sexuality

  • Anonymous on 11.16.2010 at 8:16 am

    Maybe you should also present the viewpoint of some notable researchers who believe homosexuality is NOT necessarily biologcallh predetermined. Because there is overwhelming evidence that points the other way too.

    Personally I think it falls out somewhere in the middle between 100% nature and 100% nurture.

  • Anonymous on 11.16.2010 at 8:38 am

    Christianity takes a lot of hits for being anti-gay but I have to say that in my Catholic high school the students were by far more supportive of gays than my public high school friends and especially my non-religious friends.

  • Anonymous on 11.16.2010 at 1:20 pm

    Doesn’t research that shows that family members are more likely to be gay if another is equally lend itself to the conclusion that “nurture” is the root cause? (seems this research could lead to either conclusion if they are not involving genetics, etc…_

  • To ``Maybe you should also'' on 11.16.2010 at 1:47 pm

    But he's not saying it's 100% nature or nurture

    To “Maybe you should also”:

    The speaker is not saying that it is 100% nature or nurture. I think he is saying that nature plays a big role, and now we have stronger evidence to confirm this. This does not imply that it is all nature. It only implies that the evidence we have for saying nature is now stronger. This is natural, because our tools for gathering and examining evidence have improved many fold over the past few decades.

  • Jenny on 11.16.2010 at 5:21 pm

    It shows it is largely genetic because the experimenters used a control group. The control group, adopted siblings who are gay, had only a 5% correlation – the nurture made little impact and the genomes were utterly different. Furthermore, fraternal twins, who have genes as different as siblings but the same basic nurture, are 22% correlated, while nonfraternal twins, ones with much closer genetics, are 52% correlated. So nature plays a big role.

    • winoceros on 04.18.2012 at 1:01 pm

      That is not a control group. A control would be identical twins raised together versus identical twins raised apart, in sufficient numbers so as to form a usable sample.

      Using identical twins and fraternal twins raised in practically the same environment isn’t a control. It’s very interesting, but it makes no case for biological determinance. Twins are treated very differently from non-twin siblings. This really can’t be controlled for in a non-longitudinal study.

  • Anonymous on 11.16.2010 at 5:42 pm

    A person is no more born a homosexual than they are born a heterosexual. If my sexuality is genetic, then there also has to be a gene that explains the behavior of those involved in beastiality and sex with children (even infants). It is substantially more reasonable that a person is born sexual, period; and for any number of reasons, chooses how to act on that sexuality. This also explains how people’s views on how to “act out” their sexuality change over time.

    Christian or not — sin or not — legal or not — people will act out their desires. Making this a genetic issue suddenly makes this “not my fault”. If I’m a drug addict, chances are somewhere along the line, I made a decision. If I’m a practicing homosexual, same thing. I choose.

    If it’s genetic, then it isn’t my choice. My eyes are blue. That’s genetic.

    • zdoc on 08.11.2012 at 12:10 am

      wrong. first, the a priori “reasonableness” of your position is debatable. the notion that anyone chooses whom to be attracted to seems eminently unreasonable. second, even if the nurture side were more reasonable than the nature side, science does not answer questions by adverting to reasonableness. if it did, the earth would still be flat and an electron would be either a particle or a wave. while homosexuals do make the decision to have gay sex, that hardly implies that they decided to be attracted to same-sex partners. finally, because one element of sexuality is genetically determined, that does not mean that all elements of sexuality are. your eyes may be blue but mostly they just appear to be closed.

      • Unknown on 12.30.2012 at 8:08 pm

        Sorry, nothing is debatable about it. If something is sexually genetic, then what makes incest wrong? Besides, the only reason people are against incest is because of deformations, but science and technology has invented… Wait for it… Birth Control and Condoms. OMG don’t say it is so?!

      • Unknown on 12.30.2012 at 8:09 pm

        Besides, you seem to forgotten how we get over our ex’s.

      • Mostberg on 02.23.2013 at 4:01 pm

        Nothing in the results of this study are definitive and the “reasonableness” on both sides of this issue are about equally valid at this point in time. What should be obvious to every one though is the gay community is desperately looking for science to back them up that: they were born that way. It is about equally true that conservative are equally determined to have supporting evidence that being gay is environmental. The real scientists have yet to weigh in with any factual data that proves things either way. The Pyschologist leader of this study rightly said he is unqualified to make a genetic statement on the subject. Meanwhile both sides of this issue should be a little more humble and kindly toward each other. They have only anecdotal information and minor correlations. And that is not science.

  • shadow_man on 11.16.2010 at 11:36 pm

    Homosexuality is not a choice. Just like you don’t choose the color of your skin, you cannot choose whom you are sexually attracted to. If you can, sorry, but you are not heterosexual, you are bi-sexual. Virtually all major psychological and medical experts agree that sexual orientation is NOT a choice. Most gay people will tell you its not a choice. Common sense will tell you its not a choice. While science is relatively new to studying homosexuality, studies tend to indicate that its biological.

    (Change *** to www)
    Gay, Straight Men’s Brain Responses Differ

    • Unknown on 12.30.2012 at 8:10 pm

      Sure I can choose who I am sexually attracted to. Example: My ex’s.

      • Anonymous on 10.12.2014 at 6:48 pm

        Ah, but why are you not attracted to a person you once were before? The answer: the personality of the other person. At first, you were attracted to your “ex.” Over time, that attraction dissipated as you learned more about them, and no longer wanted to be with that person. What difference does the person’s scientific sex make? Not very much. Every person has their own distinct personality, which is where (I believe) the nurture element of this debate comes into play. For instance, does one choose to be viewed as annoying for telling the same stories over and over again? No. Most likely, that is the type of person they were raised around; however, that does not change the fact that for some reason, they were initially attracted to you. Surely, you’ve met someone who was attracted to you but you were not at all attracted to them. Maybe they were a normal person with no real “deformities,” mental or physical, you just simply did not want to be with that person on a more intimate level. Why? That’s just how you were wired. You do not choose who you want to be friends with if the other person does not want to be your friend as well. Love is not a conquest to be chosen; it is a treasure to be found.

  • Anonymous on 11.17.2010 at 2:28 am

    the nature/nurture distinction is one that is increasingly irrelevant in current biological work, with the advance of epigenetics and the advanced understanding of developmental biology. framing this debate and most other discussions in these terms is not very fruitful… let’s say you have a whole array of genetic dispositions – what your physical and cultural environment exposes you to will have an enormous effect on which genes get turned on and off. this starts in the womb and never stops. nature or nurture? exactly.

  • Anonymous on 11.19.2010 at 2:54 pm

    To "A person is no more born a"

    I’m sorry. I know this type of argument encourages critical thinking and the mind in general, but your comment is simply stupid.

    • winoceros on 04.18.2012 at 1:10 pm

      Of course it isn’t. It is logical, but you disagree with the conclusion. Either there are genetic elements to sexual preference or there are not.

      The choice isn’t necessarily the attraction, as gay people and pedophiles will tell you. The choice is to act upon the attraction. If one isn’t religious and doesn’t believe homosexuality is immoral, it shouldn’t matter if a person acts on that attraction, as long as it is legal. If it is not legal, then regardless of one’s predilictions, one should not act on it.

      We should not conflate the individual moral and biological arguments with societal decisions about what makes a society “work.”

      There is nothing wrong with making a genetical sexual case for all matters of attraction. What is the difference between sexual attraction and those who can’t stop gambling? Or hoarding cats? Or addiction? The same reinforcing pleasure mechanisms in the brain are at work. That isn’t a causal argument, but there is no reason to exclude that premise because if one accepts that, one must accept a marriage argument for siblings and multiple partners. There is simply no biological distinction.

      Policy matters should be argued on a basis of societal worth, not individuals’ preferences.

  • Anonymous on 11.21.2010 at 3:21 pm

    Re: "A person is no more born a"

    I agree entirely with this post.
    Especially the part about the comparison with bestiality and pedophilia; it logically makes sense. Reason triumphs in your argument…however, you will most likely be met with hostility…that is the way of the “emotionally driven”.

  • Anonymous on 12.27.2010 at 10:33 pm

    Pillard is correct but one part bothers me

    I agree with Pillard completely in that I believe homosexuality is a function of the way you’re wired; you’re born with it. No one would willingly choose to be a minority that society has ridiculed and deemed less than equal. I’m not gay but I am a middle-aged woman and I’ve dealt with discrimination from men my entire life. It is very difficult to be a minority – so why would anyone choose that if they could avoid it? I believe that Pillard’s work will be supported soon and there will be additional evidence brought forward to corroborate it.

    What I found disturbing about the interview though was his assertion that he is a hard-core atheist. I would like to appeal to Pillard’s scientific side and ask that he read the book: “The Case for Christ: A Journalist’s Personal Investigation of the Evidence for Jesus” by Lee Strobel. It is written by an ex-atheist who set about making a case to debunk Jesus as the Christ. Instead he found, after extensive scientific and legal analysis, that it was impossible to draw that conclusion. As a result of his research Strobel is no longer an atheist.

  • Anonymous on 02.02.2011 at 2:00 am

    It was Evelyn Hooker.

  • Donald McGaw on 05.01.2014 at 7:52 am

    Ah Richard — what a delight to read your comments. Brought back so many wonderful memories of our work together at HCHS! Guess at our mutual age of 80 we are both still in there working to end discrimination toward GLBT persons. I have used the twin study in lectures here in Florida and found the audience excited about the results. I have no doubt orientation is genetic – how it is expressed, lived is nurture. That is no different than heterosexual orientation. It is curious how in the 21st century homosexuality still scares the hell out of people. Fear then brings corrupt theology and philosophy, and pseudoscience. Keep up the good work dear friend.

    • No name on 05.08.2014 at 8:14 am

      My 16 yr. old daughter recently “came out” to me. She expressed having felt “different” for quite some time and was only now able to understand what she was feeling. I held off telling my husband because I didn’t think he would accept what she was telling me. I finally did tell him and sure enough his response was, “let’s see how she feels in a few years”. I was speechless. We are at complete opposing sides on whether she was “born this way” or whether she is “choosing” to be gay. I’m so saddened by his response and I’m not sure how I deal with him going forward. I love and support my daughter 100% and want her to know that (I have told her so) If she knew how my husband felt I believe it would push them even farther apart (she chose not to tell him herself and told me I could)Do you have any advice?

  • Jeff on 03.05.2015 at 10:23 pm

    Anne Heche chose a man after being with a woman…Seems happy to me

    Would this just be an anomaly?

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