September 08, 2008

Balancing selection and homosexuality

The idea in this paper is that the genetic factors leading one to be homosexual also lead one to have higher mating success if he turns out to be heterosexual.

The use of "lifetime number of opposite sex sexual partners" as a stand-in for reproductive success is fairly problematic. It seems more likely that a couple that marries young with limited pre-marital experience will have a higher number of children than individuals who spend a lot of time having sex with multiple people (not to mention the risk to one's health from such behavior).

In my own opinion (see Beautiful Wives and Gay Sons) homosexuality is rooted in a side-effect of the expression of femininity-- or masculinity-enhancing traits in individuals of the wrong gender: if, e.g., a couple has an excess of "feminine" DNA between them, it may produce reproductively successful daughters but sons at higher risk for homosexuality. These genes are more successful (than average) in female bodies, and less than average in male ones: thus they are maintained in the gene pool.

There is a good case to be made, however, for a link between homosexuality and promiscuity. A certain lack of inhibition may be linked to the expression of the homosexual phenotype; this may explain why homosexuals tend to have more partners than average compared to heterosexuals. 

Evolution and Human Behavior doi: 10.1016/j.evolhumbehav.2008.07.002

Genetic factors predisposing to homosexuality may increase mating success in heterosexuals

Brendan P. Zietsch et al.

Abstract

There is considerable evidence that human sexual orientation is genetically influenced, so it is not known how homosexuality, which tends to lower reproductive success, is maintained in the population at a relatively high frequency. One hypothesis proposes that while genes predisposing to homosexuality reduce homosexuals' reproductive success, they may confer some advantage in heterosexuals who carry them. However, it is not clear what such an advantage may be. To investigate this, we examine a data set where a large community-based twin sample (N=4904) anonymously completed a detailed questionnaire examining sexual behaviors and attitudes. We show that psychologically masculine females and feminine men are (a) more likely to be nonheterosexual but (b), when heterosexual, have more opposite-sex sexual partners. With statistical modelling of the twin data, we show that both these relationships are partly due to pleiotropic genetic influences common to each trait. We also find a trend for heterosexuals with a nonheterosexual twin to have more opposite-sex partners than do heterosexual twin pairs. Taken together, these results suggest that genes predisposing to homosexuality may confer a mating advantage in heterosexuals, which could help explain the evolution and maintenance of homosexuality in the population.

Link

22 comments:

Dragon Horse said...

"The use of "lifetime number of opposite sex sexual partners" as a stand-in for reproductive success is fairly problematic. It seems more likely that a couple that marries young with limited pre-marital experience will have a higher number of children than individuals who spend a lot of time having sex with multiple people (not to mention the risk to one's health from such behavior).
"

I believe this. I also believe that people who marry not long after meeting (maybe a year or two) as compared to people who marry after years of dating each other have more kids.

Why? People get bored, especially men. Sex with a new woman is exciting but after awhile the "thrill wears off" and people naturally do it less, especially as they get older.

So a young couple who have not had sex a lot with each other will likely produce more children (plus fertility in both sexes is higher at younger ages anyway).

": if, e.g., a couple has an excess of "feminine" DNA between them, it may produce reproductively successful daughters but sons at higher risk for homosexuality. "

First thing I thought of was Angelina Jolie and her brother, great example.

Maju said...

this may explain why homosexuals tend to have more partners than average compared to heterosexuals

This is surely not true for homosexual women. In fact it has been often suggested that male homosexual promiscuity is just "normal male behaviour" (i.e. males tend to be more promiscuous than females). The case is that hetero males also tend to be promiscuous, even if that behaviour is often canalized via prostitution.

Dienekes said...

Homosexual men report a great number of sex partners than heterosxeual men, so it's not just "normal male behavior".

I wouldn't be surprised that female homosoexuals aren't as promiscuous, since male and female homosexuality are clearly different things (as evidenced by their much different prevalence).

Female homosexuality is, in my opinion, linked to either fear of intercourse or unattractiveness, and both factors would predispose one to have fewer sex partners.

Maju said...

Female homosexuality is, in my opinion...

In your opinion...

I know very beautiful lesbians certainly and extrovert ones as well. I don't think intercourse is an issue here either (i.e. lesbians may practice intercourse with toys). The reasons are probably varied though in my experience (and I probably know many more homosexual of both genders than you do) tomboy-ness may be a frequent (but not necessary) factor (though some studies suggest it's not).

What is clear is that women, be them lesbians or not, are much less promiscuous than men.

Homosexual men report a great number of sex partners than heterosxeual men, so it's not just "normal male behavior".

There is clearly a sector of hetero males who are very promiscuous anyhow. I mentioned prostitution, which is maybe themost common expression in our spacetime but in other realities, concubinage, polygamy, etc. have also played their role.

Maybe the differences are only due to availability of partners. Many straight men would just never participate in prostitution (not just an ethical issue but also one of self-esteem and the very nature of the pleasure obtained) and may not be able to get female partners easily (because of lesser promiscuity and/or greater selectivity of females). Such constraints probably do not act among homosexuals, specially in our modern reality.

In other words: a guy who wants a relatonship may find it easier if:

1. Is very attractive (physical, personality or both)
2. Has a high social status / loads of money
3. Doesn't mind participating in "lower" kind of relationships like prostitution
4. Is gay: his potential partners are also very open to promiscuity because they are men

In mathematical terms: say the average man has a promiscuity intention factor (PIF) of 3, and say the standard woman has a PIF of just 0.5. The effective promiscuity factor (EPF) for gays would be 3*3=9, while the EPF for straight men would be 3*0.5=1.5. Logical, isn't it?

Dienekes said...

In your opinion...

I know very beautiful lesbians


I presume you realize the irony of pointing out the subjectivity of my opinion and at the next sentence invoking anecdotal evidence.

If very beautiful female homosexuals exist in any great numbers, surely some of them would have made it to the entertainment/fashion industry which thrives on looks. Any examples?

I don't think intercourse is an issue here either (i.e. lesbians may practice intercourse with toys)

Intercourse isn't the same as using toys.

Maju said...

I presume you realize the irony of pointing out the subjectivity of my opinion and at the next sentence invoking anecdotal evidence.

Conceded.

Intercourse isn't the same as using toys.

I meant dildos... what's the difference?

Dienekes said...

You see no difference between intercourse with a live man and using a dildo? I did not speak of fear of penetration, but of fear of intercourse.

Maju said...

I think you mean "fear" (or more properly dislike) of doing it with a man - whatever the reasons behind: dislike of male body or psychology or whatever. Or maybe just preference of female qualities over male ones - some lesbians are more "open" (bisexual?) but still prefer women over men.

I understand "intercourse" as penetration - and obviously it's not the problem here.

Marc said...

Homosexual men report a great number of sex partners than heterosxeual men, so it's not just "normal male behavior".

What Maju said. Heterosexual men are limited in the number of partners they can have by the fact that their partners are women, who have different attitudes toward sex. Prostitution doesn't bridge the gap for a whole slew of reasons. Gay male promiscuity is just another instance of men behaving in an extreme manner when cut off from the mitigating influence of women.

If very beautiful female homosexuals exist in any great numbers, surely some of them would have made it to the entertainment/fashion industry which thrives on looks. Any examples?

Lesbians are, what, 1% of the female population? And you have to take into account personality. I've known plenty of quite attractive "lipstick lesbians" but even they were not overly feminine, psychologically speaking. I doubt that you will find that an attractive lesbian will have the same interest in fashion, on average, as a comparably attractive heterosexual woman on account of having a somewhat more masculinized brain.

I'm not arguing there isn't truth to the unattractive butch lesbian stereotype, but I've known a lot more gay folk than you have, Dienekes, and there are plenty of good looking dykes out there.

Dienekes said...

Heterosexual men are limited in the number of partners they can have by the fact that their partners are women, who have different attitudes toward sex.

Not really a valid explanation. If women were perfectly monogamous, then that would constrain men's ability to have multiple partners.

However, in real life, there is a sizable minority of women who are polyandrous, and so men who want to have multiple sex partners are not thus constrained.

Heterosexual men have less partners than homosexual men, because they are more likely to be in faithful committed relationships for prolonged periods of time or to seek such relationships.

I doubt that you will find that an attractive lesbian will have the same interest in fashion

Won't stop her from earning good money in fashion if she has "model looks".

I've known a lot more gay folk than you have, Dienekes, and there are plenty of good looking dykes out there.

Invoking personal experience is always a conversation stopper.

If such very attractive female homosexuals exist, where are they?

Maju said...

Lesbians are, what, 1% of the female population?

There's more data on male or homosexuality but anyhow figures seem to vary wildly (check for instance Wikipedia: Demographics of sexual orientation). Probably the figure is somewhat larger for the most strict aception and surely much larger when it includes bisexuality and the so-called "bi-curiosity". It would seem that, in spite of the modern trend to focus on exclusive homosexuality, bisexuality is in fact much more common.

I've known plenty of quite attractive "lipstick lesbians" but even they were not overly feminine, psychologically speaking. I doubt that you will find that an attractive lesbian will have the same interest in fashion, on average, as a comparably attractive heterosexual woman on account of having a somewhat more masculinized brain.

Just for the record, for me attractiveness is more like natural beauty (I just hate makeup). Nothing to do with "feminity".

...

If women were perfectly monogamous, then that would constrain men's ability to have multiple partners.

I would not argue that women are "perfectly monogamous". I'd say that more chosy in general - moreso for an extra relationship. But the overall trend is that women are significatively more monogamous than men.

Anyhow I already listed an array of ways promiscuous men can have multiple hetero relationships without women being particularly promiscuous (except for money, what falls in the realm of business, not preference).

But, besides innate inclinations, there are also social constraints: an active promiscuous man is often envied, a promiscuous woman despised instead (called "whore" and things like that). Plus the fact that motherhood seems to demand (up to a point) a stable monogamous relationship for many pragmatical reasons.

Not sure what is genetic, epigentic, cultural or just mere pragmatism... but all adds up in the same direction.

Heterosexual men have less partners than homosexual men, because they are more likely to be in faithful committed relationships for prolonged periods of time or to seek such relationships.

Or even to have no relationships at all. There's always a sizeable fraction of (hetero) men in that situation even in the most sexually active periods of life. Maybe not permanently but for longer periods in any case.

Women (hetero women), excepting maybe the less attractive or shy, normally have no problem finding a partner - another thing is their desired partner.

"I doubt that you will find that an attractive lesbian will have the same interest in fashion"

Won't stop her from earning good money in fashion if she has "model looks".


But just for lack of interest, she's not likely to look into that career (not to mention all the behind the scene stuff - what she may dislike even more). There may be exceptions, I guess (for example Stephanie Adams).

Invoking personal experience is always a conversation stopper.

Personal experience is not a scientifical study but, if among my friends one out of 5 (or maybe out of 10) is homosexual, I may know something more than someone who knows nearly no one with this tendency. Maybe not much more but experience does matter.

If such very attractive female homosexuals exist, where are they?

In "ambient" pubs? At home? In feminist associations... you know. Most homosexuals of either gender I've met, I've met them in leftist organizations or related enviroments (where they may feel more "at home", where their socio-emotional needs are better served). You probably do not frequent such enviroments, just that.

But anyhow, check Wikipedia: List of gay, lesbian or bisexual people (two dozen lists in fact) to check for famous lesbians, some of them really beautiful (the lists are dominated by men anyhow, as happens in nearly everything).

Dienekes said...

There are plenty of female homosexuals working in fashion, just not in front of the cameras.

The claim that they aren't interested in fashion isn't based on any empirical evidence that I know of. Even if true, there is a perfectly good explanation for it: unattractiveness.

Anyhow, check Wikipedia: List of gay, lesbian or bisexual people (two dozen lists in fact) to check for famous lesbians, some of them really beautiful (the lists are dominated by men anyhow, as happens in nearly everything).

Who do you have in mind? And, no, "bisexual women" don't count.

Maju said...

The claim that they aren't interested in fashion isn't based on any empirical evidence that I know of. Even if true, there is a perfectly good explanation for it: unattractiveness.

Certainly your claim of unattractiveness is not empirical either. It seems a very subjective claim.

Who do you have in mind? And, no, "bisexual women" don't count.

Why not. One of the main problems I percieve when discussing homosexuality is the nonsense of focusing only in pure homosexuals, who obviously are a minority of all people with homosexual tendencies of some sort.

Bisexuality should be the main field for study of homosexuality, IMO, as it's obvious that there are many more bisexual than pirely-homosexual people, that the latter are just the extreme case in a gradation. Certainly homosexual organizations in my country have recieved the latest studies on homosexuality (all curiously released just before June 28) with great caution and some skepticism, emphasizing the fact of relatively common bisexuality as an important transition ignored by such papers.

As for the concrete examples, I just browsed the lists and found some really beautiful women among them (what did not surprised me the least). I am not really interested in chit-chat nor in the personal lifes of famous people and I am not going to spend several days researching if this or that person mentioned is purely homosexual or "just bi".

I really don't care. A good number will be bisexual, of course(as bisexuality is more common than pure homosexuality). I don't think that really matters, except for the individual making such decissions in his/her personal life.

It is possible that homosexuality in women is not as much genetically influenced as among men, that I concede (on light of the research I have read) but I don't think that it has to do with attractiveness. In fact I cannot recall a single ugly lesbian: average or somewhat "masculine" yes, but not strikingly ugly. There must be some but I have not meet them yet.

Dienekes said...

Certainly your claim of unattractiveness is not empirical either. It seems a very subjective claim.

It is not subjective, as people tend to associate homosexuality with unattractive people.

and:

"In a survey of 648 women, we compared various cardiovascular risk factors between 324 lesbians age 40 and older residing in California and their heterosexual sisters closest in age. Compared with their sisters, the lesbians had a significantly higher body mass index, waist circumference, and waist-to-hip ratio (WHR)."

So, I'm not alone in my perception that lesbians are unattractive, and they also are less attractive according to objective criteria.

Bisexuality should be the main field for study of homosexuality, IMO, as it's obvious that there are many more bisexual than pirely-homosexual people, that the latter are just the extreme case in a gradation.

The discussion was about female homosexuals. The definition of "homosexual" is not the same as the definition of "bisexual".

Obviously "bisexual" women who have sex with men don't have a major problem with either attractiveness or fear of intercourse. The discussion was not about these women.

Maju said...

That a prejudice associated homosexuals with unattractiveness is widespread doesn't mean that homosexuals are unattractive. They did not study that, just subjective perceptions, stereotypes.

The other paper may have some relevance but only regarding weight issues, that normally only appear at middle age. It does not really evaluate innate attractiveness.

I remain skeptical and with good reason.

Obviously "bisexual" women who have sex with men don't have a major problem with either attractiveness or fear of intercourse. The discussion was not about these women.

I have known lesbians who have suddenly become hetero and vice versa. It may be one of the common forms of bisexuality as measured through someone's lifetime. Most people (and that may be particularly true for women) only have one main relationship at a time (I think they call it sequential monogamy - or maybe it's sequential polygamy?) so if one is involved with another woman at some time, she won't probably have heterosexual relations and when she becomes involved with a man she will probably not keep homosexual relations simulatenously. Yet, measured through a lifetime record such person should be considered bisexual and they will probably report themselves as such.

In any case, what do you base your claim of "fear of intercourse" on? I cannot but read this claim of yours as prejudiced spelling of "dislike of men" (in the context of personal relations).

In fact I was briefly involved in a personal relationship with a close lesbian friend who I consider fully lesbian in any case: she was bi-curious in my case and had also another young-age hetero relationship. Nowadays she's happily "married" with another woman and all other relationships I know of were with women.

And, yes, she developed some belly upon reaching her 40s but she used to be very slender before that.

Marc said...

However, in real life, there is a sizable minority of women who are polyandrous, and so men who want to have multiple sex partners are not thus constrained.

This is simplistic. A culture made up of a mix of people who are mostly polyandrous (men) and mostly not (women) is going to be very different from a culture, like the gay male subculture, created by people who are mostly polyandrous. The latter will be far more accepting of polyandry and will provide for more opportunities for it. The former, on the other hand, will still have a number of social constraints on such behavior, as well as at least some expectation of monogamy.

Invoking personal experience is always a conversation stopper.

Really? How so? This conversation seems to be proceeding. :)

If such very attractive female homosexuals exist, where are they?

Dienekes, what do you want? Seriously, do you want me to round up some attractive female homosexuals whom I know and fly them to Greece to meet you?

So, I'm not alone in my perception that lesbians are unattractive, and they also are less attractive according to objective criteria.

I certainly don't think there are as many attractive lesbians, on average, as there are attractive straight women and I don't recall arguing such. Lesbians really do have a more masculine/frumpy appearance on average than straight women. I've heard attractive lesbians complain about this. But there's still a great deal of variety among gay women, just as there's a great deal of variety among straight women.

A quick google search turned up two women who are lesbians and have made a career in front of the camera. I guess taste is subjective and I don't think the former has aged well since her time on Ally McBeal, when she was HOT. But here you go:

Porscia (Sp?) Di Rossi (Ellen's wife)

http://images.askmen.com/galleries/actress/portia-de-rossi/pictures/portia-de-rossi-picture-2.jpg

Kim Stolz

http://cache.daylife.com/imageserve/0fpe7nz8470xT/610x.jpg

Anyway, I do want to make clear that I'm not saying that the "lesbians are unattractive" stereotype is off-base. There's a lot of truth to it. I'm just saying I've known plenty of lesbians who don't fit that stereotype, including some who were downright stunning.

Dienekes said...

More

"Adjusted multinomial logistic regression analyses showed lesbians have more than twice the odds of overweight (odds ratio [OR]=2.69; 95% confidence interval [CI]=1.40, 5.18) and obesity (OR=2.47; 95% CI=1.19, 5.09) as heterosexual women."

in any case, what do you base your claim of "fear of intercourse" on?

The fact that they are more likely to have been sexually abused as children or adolescents

"Comparing physical abuse victimization occurring in both childhood and adolescence, lesbian (30%, prevalence ratio [PR] 1.61, 95% confidence interval [CI] 1.40, 1.84) and bisexual (24%, PR 1.26, 95% CI 1.00, 1.60) women were more likely to report victimization than were heterosexual women (19%)"

and:

"In hierarchical linear modeling analyses, sexual orientation was a significant predictor of most of the victimization variables. Compared with heterosexual participants, LGB participants reported more childhood psychological and physical abuse by parents or caretakers, more childhood sexual abuse, more partner psychological and physical victimization in adulthood, and more sexual assault experiences in adulthood."

or:

"Overall, bisexual or lesbian respondents were about as likely as heterosexual women ever to have had intercourse (33% and 29%, respectively), but they had a significantly higher prevalence of pregnancy (12%) and physical or sexual abuse (19-22%) than heterosexual or unsure adolescents."

So, yeah, I'd say my theory that female homosexuality is related to unattractiveness and fear of intercourse corresponds to the known facts quite well.

But I'm willing to consider the possibility that an attractive female without any traumatic experiences in her past will grow up to be homosexual. [If any evidence for that unlikely claim is presented, besides the "I know one" claim]

Marc said...

But I'm willing to consider the possibility that an attractive female without any traumatic experiences in her past will grow up to be homosexual. [If any evidence for that unlikely claim is presented, besides the "I know one" claim]

Dienekes, even your data suggests that the majority of data have not experienced physical or sexual abuse. If 30% of lesbians experienced abuse in childhood or adolescence as your second study claims, than what of the other 70%? Is their homosexuality caused by their being unattractive? And if unattractiveness causes female homosexuality, then why aren't more women gay? The number of women I'd say are unattractive is a lot higher than 1-3%. Most people aren't lookers.

I'd say the data suggests a relationship, but there's a lot that goes into sexuality.

"A group of researchers at the University of Texas found structural differences in the inner ears between lesbians and heterosexual women... ...The researchers found that lesbians had inner ear characteristics that were more like those of men. The structure of the inner ear forms before birth and is affected during pregnancy by androgens. These findings indicate that sexual orientation is at least partly decided before birth -- perhaps at conception."

http://www.religioustolerance.org/hom_caus6.htm

Also:

Cerebral responses to putative pheromones and objects of sexual attraction were recently found to differ between homo- and heterosexual subjects. Although this observation may merely mirror perceptional differences, it raises the intriguing question as to whether certain sexually dimorphic features in the brain may differ between individuals of the same sex but different sexual orientation. We addressed this issue by studying hemispheric asymmetry and functional connectivity, two parameters that in previous publications have shown specific sex differences. Ninety subjects [25 heterosexual men (HeM) and women (HeW), and 20 homosexual men (HoM) and women (HoW)] were investigated with magnetic resonance volumetry of cerebral and cerebellar hemispheres. Fifty of them also participated in PET measurements of cerebral blood flow, used for analyses of functional connections from the right and left amygdalae. HeM and HoW showed a rightward cerebral asymmetry, whereas volumes of the cerebral hemispheres were symmetrical in HoM and HeW. No cerebellar asymmetries were found. Homosexual subjects also showed sex-atypical amygdala connections. In HoM, as in HeW, the connections were more widespread from the left amygdala; in HoW and HeM, on the other hand, from the right amygdala. Furthermore, in HoM and HeW the connections were primarily displayed with the contralateral amygdala and the anterior cingulate, in HeM and HoW with the caudate, putamen, and the prefrontal cortex. The present study shows sex-atypical cerebral asymmetry and functional connections in homosexual subjects. The results cannot be primarily ascribed to learned effects, and they suggest a linkage to neurobiological entities.

http://www.pnas.org/content/early/2008/06/13/0801566105.abstract

Dienekes said...

Porscia (Sp?) Di Rossi (Ellen's wife)

With Ellen's bank balance and undeniable sense of humor, she can pick the best. Although someone who was married isn't exactly a poster girl for homosexuality.

Kim Stolz

Nothing special.

http://www.villagevoice.com/2005-11-29/nyc-life/beauty-and-the-modeling-beast/2

"You have an unabashed love of McDonald's, which you claim you ate a couple times a week in college. Would you get comments about what you ate during the show from others? Those girls are tiny. It's unbelievable. Certainly, besides the plus-size model, I weighed more than those other girls did."

Dienekes said...

Dienekes, even your data suggests that the majority of data have not experienced physical or sexual abuse. If 30% of lesbians experienced abuse in childhood or adolescence as your second study claims, than what of the other 70%? Is their homosexuality caused by their being unattractive?

You got it.

Although having a teen pregnancy or being abused in childhood isn't the only way one may develop a phobia of sex. I just mentioned it since the idea that "fear of intercourse" was a factor was challenged.

.The researchers found that lesbians had inner ear characteristics that were more like those of men. The structure of the inner ear forms before birth and is affected during pregnancy by androgens. These findings indicate that sexual orientation is at least partly decided before birth -- perhaps at conception."

Yet another argument in favor of my theory that female homosexuality is caused by masculinization, which -we'll agree- makes women less attractive.

and:

" Whether women describe themselves as straight or lesbian, “Their sexual arousal seems to be relatively indiscriminate — they get aroused by both male and female images,” Dr. Bailey said. “I’m not even sure females have a sexual orientation. "

"Sexual orientation, at least for men, seems to be settled before birth. “I think most of the scientists working on these questions are convinced that the antecedents of sexual orientation in males are happening early in life, probably before birth,” Dr. Breedlove said, “whereas for females, some are probably born to become gay, but clearly some get there quite late in life.”"

Marc said...

So I guess the question we come to is whether in utero masculinization makes women gay directly or indirectly. In that case, I must disembark from the thread as I don't think I have anything substantive to add on this point.

I do find it a little odd that every lesbian with whom I've spoken about pornography (small sample size) prefers straight to lesbian porn.

Maju said...

Thanks for your documentation efforts, both Marc and Dienekes. It's interesting.

I just want to add that, while there seem to be some trends, it's not a black and white issue - not an evident one certainly.

Also all studies refer to lesbian and bisexual women indistinctly. And even there is one that claims higher risk of teen pregnancy for lesbians (what is inconsistent with fear of intercourse - though might trigger it, I guess).

In any case, it does not seem like we can just declare that "lesbians are..." in general. Even if there are statistically significative trends, a 30% versus 20% (for example) is still a small difference, certainly not enough to end up with black and white conclussions.

That's all.