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How did you get to be heterosexual? Homosexual? Bisexual? Was it nature or nurture (or both?). Were you born with a sexual orientation or did it develop as you grew? What role did your parents play? In this episode I present the most recent scientific research on the topic of how we develop our sexual preference. You’ll find out whether heterosexual men have more testosterone than homosexual men, how most people know their sexual orientation when they are as young as 10 years old (blame your adrenal gland), how your third interstitial nucleus might be playing a role and finally, could it have something to do with the length of your fingers? Find out in this episode of The Psych Files.
“…we should…be asking ourselves why we as a society are so emotionally invested in this research. Will it – or should it – make any difference in the way we perceive ourselves and others or how we live our lives and allow others to live theirs? – William Byne: The Biological Evidence Challenged (1994, Scientific American)
Correction: In the first version of this episode I incorrectly estimated the number of homosexuals in the US. Assuming a US population of about 260 million with about 1/2 female and 1/2 male, then 2% (females) and 3% (males) of 260 million would equal about 6 and a half million total. I updated the audio file to include this corrected information.
Resources on Sexual Orientation
- If you would like to see the concept map I used to hold my notes for this episode click here: sexual orientation.
- If you would like to download the PowerPoint file containing these same notes click here: sexual orientation powerpoint file.
Research on Sexual Orientation
Bailey, J.M., Bobrow, D., Wolfe, M., & Mikach, S. (1995). Sexual Orientation of Adult Sons of Gay Fathers. Developmental Psychology, 31 (1), 124-129.
Bell, A., Weinberg, M., & Hammersmith, S. (1981). Sexual preference: Its development in men and women. Bloomington: Indiana University Press.
Bem, D.J. (1886). Exotic becomes erotic: A Developmental theory of sexual attraction. Psychological Review, 103, 320-335.
Byne, W. (1994). The Biological Evidence Challenged. Scientific American, May.
Ciccarelli, S. & Meyer, G.F. (2006). Psychology. Prentice Hall.
Cantor, J.M., Blanchard, R., Paterson, A.D. & Bogaert, A.F. (2002). How many gay men owe their sexual orientation to fraternal birth order? Archives of Sexual Behavior, 31, 1; Psychology Module.
Gladue, B.A, The BioPsychology of Sexual Orientation. in Current Directions in Human Sexuality and Intimate Relationships, Fisher, T.D. & McNulty, J. eds. Allyn and Bacon.
Hock, R. (2010). Human Sexuality, 2e. Prentice Hall.
Kendler, K.S., Thornton, L.M., Gilman, S.E., & Kessler, R.C. (2000). Sexual orientation in a U.S. national sample of twin and nontwin sibling pairs. The American Journal of Psychiatry, 157; 11; Health Module.
King, B.M. (2005). Human Sexuality Today. Prentice Hall, 5e.
Levay, S. (1991). A difference in hypothalamic structure between heterosexual and homosexual men. Science, 253, 1034-1037.
McClintock, M.K. & Herdt, G., Rethinking Puberty: The Development of Sexual Attraction in Current Directions in Human Sexuality and Intimate Relationships, Fisher, T.D. & McNulty, J. eds. Allyn and Bacon.
McFadden, D., Loehlin, J.C. and Pasanen, E.G. (1996) Additional findings on heritability and prenatal masculinization of cochlear mechanisms: Click-evoked otoacoustic emissions. Hearing Research, 97, 102-119.
Patterson, C.J. (2000). Family Relationships of Lesbians and Gay Men, Journal of Marriage and Family, 62, 1052-1069
Rind, B. (2001). Gay and bisexual adolescent boys’ sexual experiences with men: an empirical examamination of psychological correlates in a nonclinical sample. Archives of Sexual Behavior, 30 (4).
Selekman, S. (2007). Homosexuality in children and their parents. Pediatric Nursing, 33(5).
Smith, B. (2007). The Psychology of Sex and Gender. Allyn and Bacon.
Toates, F. (2007). Biological Psychology. Prentice Hall.
Wood, S.E., Wood, E. G., & Boyd, D. (2005). The World of Psychology, 5e. Allyn and Bacon.
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{ 10 comments… read them below or add one }
Perfect timing! We just started a Nature v. Nurture unit in my classes!
Great! Well, don’t forget to grab the powerpoints if you like.
Fascinating show – well presented, scientific and neutral on a sometimes-controversial topic. Since I know you are dedicated to presenting evidence-based observations, I hope you will appreciate some comments regarding the observations of homosexual behavior among animals. In this forum, I hope I won’t need to explain that my comments are meant in the same neutral and scientific tone you adopted, pursuing the scientific truth regardless of whether the outcome is consistent with my preconceptions.
Cow Mounting Behavior
I grew up on a farm, and we all knew that when one cow (female) started mounting another cow, it was because the second cow was in heat (ready for breeding). No one thought this behavior was homosexual or positioned anywhere along a straight-homosexual continuum. I guess I didn’t reflect on it much at the time, but, from an evolutionary perspective, I would categorize this mounting behavior it as some sort of harmless adaptive misfire. After all, under evolution, lots of adaptations arise that are not necessarily beneficial. Of course, if anyone can suggest a reason why this quasi-homosexual behavior could be explained as beneficial, I’d be open to it, if supported by evidence.
Homosexual to the Point of Missing Reproductive Opportunities?
So, in a related vein, I wonder if you have found any examples in the scientific literature whereby animals exhibit homosexual behavior to the degree that they forgo breeding opportunities. From an evolutionary perspective, passing on one’s genes is not just top priority; it is practically the only thing that matters.
Is Human Homosexuality Significantly Different than Animal?
Unlike animals, it is apparent that many humans homosexuals regularly forgo breeding opportunities. This seems to be a fundamental difference between human behavior and that behavior exhibited by other animals. I’d love to hear what Dr. Buss has to say about this.
My Evolutionary Hypothesis for Homosexuality
One potential explanation is that homosexual behavior is somehow beneficial one’s nieces and nephews. Under this conjecture, homosexuals don’t pass on their genes directly, but contribute to the success of their sibling’s offspring to make them more successful and thus more likely to survive and pass on their genes. For this to be plausible, they would have to contribute a huge advantage to their nephews and nieces, since the genes that are being passed are not that closely related (you share half your genes with your siblings, and your niece shares only one fourth your genes); the upshot is that your children share twice as many of your genes as your nephews, so by one measure, you would need to make your sibling’s offspring twice as likely to survive.
One Way to Test the Conjecture
In order for my conjecture to be true, homosexual behavior in animals should be strongly linked to cooperative social animals, for example, lion prides, wherein some sisters cooperate to the point of actually nursing their sister’s offspring.
Homosexual Geese?
From what I know about geese behavior, I don’t think such cooperative behavior exists. So, with regard to the evidence of homosexuality in geese, I suspect that this is an exaptation or adaptive misfire rather than beneficial behavior.
Reverse Causality
On a different topic, I enjoyed your discussion of reverse causality with regard to Freud’s ideas on over-protective mother and distant fathers. I wonder if any of that kind of thinking could somehow apply to the correlation between left-handedness and homosexuality. I have heard it claimed that left-handed people have fundamentally different ways of thinking compared to right-handed folks; perhaps there could be some hidden causal link related to that way of thinking, similar to the one you proposed to counter Freud’s theories.
Dude, 3% of males and 2% of females does not equal 5% of the total population!
Actual Randy: interesting comment. Thanks for taking the time to write it. Not having grown up on a farm, I can’t say that I’ve seen this female cow behavior. I suppose it could be, as you say, a harmless adaptive misfire, but how about this – the behavior could have an evolutionary advantage if it served to signal to the male cows that the female is ready to breed. That’s my only thought on that matter.
I like your challenge to find a homosexual behavior that an animal engages in “to the degree that they forgo breeding opportunities”. That would be very interesting to find. I don’t know of any such research, but I will, as always, keep my eye open for it.
Good question for Dr. Buss. I hope to interview him again so I copied your comment over to my notes for that interview.
Again thanks for your comment. And as for Isabel’s comment – you are right about the miscalculation in the stats. I corrected this and updated the audio (which only people who download the episode now will hear – oh well).
You didn’t actually say what percentage of identical twins raised in different environments are both homosexual. If this is less than 50%, which I think it is, then this suggests that non-genetic factors play a greater role in sexuality than genetics.
With twin studies there’s a tendency for us to grasp on to any evidence of genetic influence, even when this less than 50%. At the same time, there’s a tendency to not notice how large the non-genetic influence is.
Hi Michael,
Again, you’ve done a wonderful job of addressing a potentially controversial topic (not that I consider it as such, personally). I really appreciate you addressing some of these topics that rest a little closer to home for most of us. I think it’s really important that research is done on not only what’s not controversial but also on stuff that can be considered taboo by some.
Out of interest, will you be considering an episode on gender and libido in the future? Although potentially controversial again, I think a lot of people might get a lot of benefit from it.
As an aside, an entertaining book on sex research I found was called “Bonk” by Mary Roach (though I think the title might be different in America, but I can’t remember what it was called). Very interesting and very amusingly written.
LeVay’s critics have been addressed over and over, and most of what was thrown at him was entirely baseless and driven by veiled (and not so veiled) homophobia. I really wish you’d have gone into more detail there, rather than simply saying that people criticized it. That sends the message that people should disregard his research, when truthfully it was very well carried out, and he was extremely careful not to overstate his findings. (He also got death threats after its publication, by the way.)
Your comment about his “subjects” might have been in regard to the fact that many of the brains of gay males had been from people who died from complications due to AIDS. That is true, and was trumpeted as a major flaw since the HIV virus can affect brain structure (although it’s never been shown to affect the hypothalamus in that way); however, LeVay also compare those measurements to the brains of the heterosexuals in the study who also had died from AIDS, and, although that left him with an extremely small sample size, he found the SAME results. Critics never seem to mention that.
The saddest part of this is that this is such a hot-button topic (after all, gays are the last group that religious groups can openly denigrate and support disenfranchisement of) that researchers in psychology and related sciences are reluctant to get involved. Even those who do often show themselves to be affected by homophobia. Michael Bailey, for instance, recently confirmed for me via email that he would support a couple’s decision to abort a child known to be homosexual if such a screening test ever became available. This is a horrific statement, and something I think most people would be shocked by if we were discussing something like eye color, handedness, or another equally non-controversial aspect of human variation. I lost a hero in that conversation.
Wow! I just listened a bit further, and I’m boiling! You just talked about one of the most important findings (finger length), and then completely disregarded it, saying, “I’m not sure what it means,” and “I just think we need to be careful…” What?! Do you say that when you discuss other topics and their findings? I doubt it.
What it MEANS (when you look at all of these things in the aggregate) is that prenatal hormone exposure is strongly involved in sexual orientation. Left-handedness, finger length, INAH-3 size, hair swirl patterns, The Older Brother Effect, and just about every other important finding regarding sexual orientation can be directly connected (in a predictable pattern) to the amount of masculinizing hormone the developing child is exposed to prenatally. Like millions of other topics in the sciences, there’s a relatively small effect size (probably due to other variations in biology that leave some of us more sensitive to this hormone exposure than others), but the patterns are undeniable. I’m not sure why you’re soft pedaling so much on this topic, but it’s uncharacteristic considering the other podcasts I’ve listened to on your site.
Sheldon: guess I didn’t make myself clear in the episode when I said “I’m not sure what it means”. Here’s what I was thinking: it could mean what you mention above – prenatal hormone exposure influencing sexual orientation, but why would hormones affect finger length? What’s the connection to fingers? Why not toes? I was wondering whether this finger-length finding is spurious – I think only one study has found this. So it’s interesting, but again – why would hormones affect the length of only one finger? What’s the theory to explain this?