Mark van Vugt Ph.D.

5 Big Ideas About The Origins of Homosexuality

The Genetics of Gayness

2012 was a reasonably good year for the International Gay and Lesbian Rights Movement. A number of countries and some states in the US have decided to legalize same sex marriages, and various openly gay politicians have been elected or re-elected for the highest political offices in their countries or states.

These trends mirror the scientific advancement that has been made in 2012 on the biology of homosexuality. The converging findings suggest that exclusive homosexuality is not a “life style choice” but a perfectly natural sexual orientation. While there is still much debate on the exact causes of homosexuality and a “gay gene” remains elusive, biological scientists agree that there is a strong genetic influence to gayness.

First, across various nations and cultures there is a relatively stable minority of people – about 8% -- with an exclusive homosexual orientation. There are twice as many men as women in this category. Second, there is converging evidence from twin studies that homosexuality “runs in families.” Third and finally, biologists have discovered forms of homosexuality in many other animal species to which humans are related to varying degrees, from baboons to dolphins and from penguins to worms.1

Although these findings make a reasonably strong claim that homosexuality is part of someone’s genotype, there is still much speculation as to how it got there. In an informative and entertaining book, titled “Homo Mysterious”, evolutionary biologist and psychologist David Barash offers a number of different scenarios for the evolution of predominantly male homosexuality, whihc is considered a moe stable trait. Here is a list of the 5 most likely evolved functions of homosexuality in humans.

1. Kin helping

This hypothesis suggests that homosexuality serves the function of providing assistance to siblings and other relatives. By refraining from producing off-spring themselves, homosexuals can invest more time and resources in rearing the offspring of close relatives with whom they share portions of their genes. The evidence for this kin helping hypothesis is mixed, however. A study in the UK comparing homosexual and heterosexual men found no significant differences in their assistance and generosity to kin such as babysitting or willingness to invest resources. Yet, research in traditional societies such as on the island of Samoa found that male homosexuals invest significantly more than male heterosexuals to support their extended family, and that they are fully accepted members of their societies.

Another version of the kin selection hypothesis is that homosexuals (as non-married individuals) occupied high status positons within their societies -- think of the monks and nuns in medieval times -- and so indirect benefits might accrue to their families.

It is thus possible that genes for homosexuality could spread in early traditional societies because of the family benefits they produced.

2. Group selection

It is also possible that homosexuality emerged because it produced benefits for the entire group. One possibility is that groups containing significant numbers of homosexual individuals got fewer children and these groups would be less likely to exhaust available resources such as food and water. Another possibility is that groups with proportionally more homosexuals would function more smoothly, because there would be fewer conflicts over access to mates (males or females). In all fairness, I do not know of any empirical evidence for this group selection hypothesis.

A third possibility that homosexuality–promoting genes were selected for because of women’s sexual preferences. The argument is that some women may have been favorably disposed towards homosexually inclined men because of their social, cooperative and empathic qualities. Thus, forming partnerships with those men may have ensured better care for children. Research indeed shows that many women find gay men appealing because they are less threatening than (some) heterosexual men who might be openly aggressive and predatory. Again this hypothesis awaits empirical investigation.

4. Balanced selection

A fourth evolutionary explanation for the stable frequency of homosexual genes in human populations is that these genes provide some ulterior benefit. The argument is that although there is negative selection for homosexual genes (because their bearers do not produce as much offspring as individuals with heterosexual genes) there may be compensating benefits. For instance, if the genes for same sex preferences would also cause an individual to have a greater intelligence or a better physical health then there would be compensating benefits, leading to the spread of homosexuality genes in a population.

5. Sexually antagonistic selection

A final possibility is that homosexuality genes might produce different effects for males versus females. It could be that when homosexual genes reside in male family members this would result in them having fewer off-spring. Yet when these same genes reside in the female family line they could result in them getting more offspring to compensate for the loss of fitness in males. There is some support for this. One study found that the mothers of homosexuals had, on average, more children than mothers of heterosexual children. And the family members of the mothers’ line in homosexuals also sired more offspring. A review study just published in the Quarterly Review of Biology provides further support for this hypothesis. It suggests that particular (epigenetic) mechanisms that suppress androgens in female fetuses -- that enable them to grow into more feminine bodies with feminine brains -- also suppress androgens in male fetuses, which has the side effect of turning them into less masculine men. If these feminine women do better than the average female in getting more children such a mechanism could result in the propagation of homosexual genes.

These are some of the evolutionary hypotheses that are out there to support the relatively well-established scientific claim that homosexuality is a natural (normal) sexual orientation. More research is needed and hopefully in 2013 scientists will come closer to solving the mystery of homosexuality.

The biological science of homosexuality suggests that rather than discussing how we feel about homosexuals and how society should treat them, we should ask ourselves why homosexuality exists and what its functions are (or were).

Exclusive homosexuality is about twice as common in men. Further, male homosexuality is considered a more stable trait by scientist so likely more heavily influenced by genes. I should mention this in blog though. Cheers, mark

Thanks for a clear overview of the main theories.
If I may give my own opinion, I think the kin selection theory is the weakest explanation among these. From an evolutionary viewpoint, not having any children oneself is a big loss, therefore the amount of help given to one's kin would have to be enormous to compensate. I was not aware of the Samoan study, which does seem to support the theory, but I do wonder if the amount of help that homosexual men in this culture provide their relatives really is enough to provide a plausible level of support for the theory. Additionally, it would make more sense from a kin selection perspective for relatives who have no children to be asexual rather than homosexual, as they would avoid distracting sexual entanglements altogether.

Personally, I think the sexually antagonistic selection and the balanced selection theories are the most plausible as they show more clearly defined benefits from a fitness perspective.

Of course a combination of factors might provide the best explanation.

Another aspect if the kin selection hyoothesis that i failed to mention is that homosexual men may hold higher status positions in their societies which might benefit their families in a different manner.

That is very interesting, I can see how a high status relative could benefit their family considerably. This raises a question about generality - how common is it across the world for homosexuals to have high social status based on their sexuality? I don't know the answer to this, I don't actually know if it has even been studied.

Surely the fact that there are bi sexual, asexual and transexual people indicates that sexuality is within a continuum thence the reason there is no "gay" gene. Like many other genes for a particular feature, the sexuality gene/s has variable expression.
Epigenetic influences may be present but the consistency of population composition tends to indicate it may not be as big an influence as sone think.

While cultural eg ancient Greeks and "Western acceptance" and learned behavior eg from abuse experiences as a child have also been postulated, what are the statistics that indicate these influences are valid? It would appear that there being no increase in homosexuals in Somoa (I'm assuming this because you did not mention there was) that "acceptance" indicates that there is no "learned" influence on homosexual behavior.

It would appear though that epigenetic changes in gene expression through hormonal influences (not including the activities which may occur in puberty) may affect some individuals within a lifetime -latency, not to be confused with delayed "coming out".

It has been postulated by evolutionary psychologists that depression may have been a genetic adaptation to slavery (a very common feature of early times) as depressed slaves were less likely to try to escape (and be killed) and hence had the chance of living longer. Is it possible variability in sexuality may have had a similar "protective" effect?

«It suggests that particular (epigenetic) mechanisms that suppress androgens in female fetuses -- that enable them to grow into more feminine bodies with feminine brains -- also suppress androgens in male fetuses, which has the side effect of turning them into less masculine men.»

I'm sorry, but this is just reiterating the stereotype according to which homosexual men are not masculine and physically "feminine" and the like; well, that's clearly wrong: I'm gay and I definitely do not look like a woman or a "less masculine man", as lots of gay men. I don't get the point in this statement. There are gay guys that are not masculine and there are gay guys who are very masculine (often more masculine than many heterosexual men), so what's the point in this? Thanks.

Kin selection has already been shown to not work in practice and, even if it could, it would not explain a homosexual orientation well (except as a rather strange, human-specific byproduct of kin selection); asexuality, maybe, but homosexual, not so much.
(See here: http://popsych.org/what-causes-male-homosexuality/)
(Also see here: http://popsych.org/is-the-exotic-erotic-probably-not/)

Group selection doesn't work either, for very good conceptual reasons that have been discussed at length in many areas.
(See here:http://popsych.org/no-really-group-selection-still-doesnt-work/)
(Also see here: http://popsych.org/no-really-group-selection-doesnt-work/)
(And also see here: http://popsych.org/group-selectionists-make-basic-errors-again/)

The sexual attraction idea makes absolutely no sense. If women preferred homosexual men because of some other traits that you're positing homosexuality might be a byproduct of, well, it would do those men's genes no good. In fact, you seem to be positing there that women might like homosexual men because those men aren't trying to have sex with them. Hard to achieve reproduction without that variable.

For balancing selection to be viable, there would need to be some incredibly devastating and common pathogen that homosexuality protects against, and even then we would only expect homosexuality to persist in the presence of that pathogen. The only known maladaptive byproduct with a comparable fitness hit is sickle-cell, and that defends against malaria, and is only common in areas where malaria is.

Sexually antagonist selection doesn't work well either: the wildly-varying concordance rates in twins don't seem to favor it well, on top of a homosexual orientation being a massive fitness hit that would require many additional offspring to offset it.

Just because there are supposedly more gay men than lesbians, doesn't mean you have to exclude them from the studies. It just brings out the whole problematic of women being excluded from movements, specially lesbians - who already went through this problem once, when "gay" alluded to homosexuals IN GENERAL, yet society - always putting men first - forgot women could be homosexuals too...so "gay" became an equal of "gay male", excluding lesbians from basically everything. That's why the jargon "lesbian" became more popular. So it's really upsetting to see my sexuality and the sexuality of my friends being excluded because we're the minority of minorities. How can you talk about the "answer to why's and how's of homosexuality" ignoring a significant part of the homosexuals? What if you find out that one of the traits only works on men...female homosexuality will remain unquestioned because women rarely matter anyways?

Well if the scientists want to prove that its genetic don't they have to find the gene instead of just relying on the theory, like how they discovered the X and Y chromosomes which determined the sex of a person.

Secondly, if we are going to believe that evolution is involved in this. According to the theory of evolution a change occurs for a beneficcial reason. Then why did evolution cause homosexuality in which there is a greater disadvantage:

1)Man to man sex is reported with greater STD and AIDs problems and then if these men have sex with a woman they infect her.

2)The population of women is more than men due to the immune system of man being weaker and there are more men dieing in events like war. And than because of homosexuality more men are reduced for women.

Thirdly, why is it that homosexuality is less occuring in certain societies or religious communities, like among christians or muslims. If its genetic that shouldn't happen. There are some people proclaiming to be ex-gay. If its genetic how can some one leave homosexuality.

In conclusion. I don't believe it is natural, but I do believe that some one can have a desire for the same-sex, otherwise they wouldn't be doing it. but desires can also be suppressed like jealousy, greed,anger.

I have a hypothesis. Marriage---Love marriage---boyfriend & girlfriend relations---Orgies---homosexuality. In this sequence you can see one after the other and in history it did happen in this sequense. In each term we see the level of lust or promiscuity increasing. maybe the desire of men of wanting more and more led him to homosexuality. Its just a hypothesis, I could be wrong.

Some problems reside therein the final paragraph of the response, above; A claim, that the prescribed order is intrinsically connected has been made, and; that there is some historical account, or timeline, that could provide a credible roadmap of the order's existence throughout history.

Regarding the first claim, I have yet to see any such evidence among scholary doctrine that suggests homosexual (or partner sharing activities) were so prevalient in pre or early human history, and I am unable to follow how your claims marriage-love marriage-relations-orgies-homosexuality are supposedly connected to one another. They're a wishful fantasy and deflection created with the intent of relieving any blame on the guilty subjects in question.

What little history we have on hand is quite recent and artful, being as much fiction and fancy as it was reality, rather than spanning back tens of thousands of years or providing anything short of hard fact. That, of course, limits its significance.

In some cases where a male is feminine, it may be genetic error, but this is hardly an excuse, and in keeping it should be a conditionally rare one.

There does not appear to have been enough time for homosexuality alone to have developed as prevalent as it appears. Thus, there is another theory, a more plausible one backed by numerous empirical studies, suggesting that homosexuality in male humans is a natural defence and developed characteristic caused by the style of upbringing.

Psychological research results that were conducted among individuals, who identify themselves as homosexuals, determined a sharp trend in their younger lives where the father figure was absent, uncaring, or unaccepting, leaving him in the care of an authoritive, overbearing and often dominating mother figure. Among most tribes, the sons would accompany the father in hunting to learn the skills, but for more developed civilizations the sons spent more time with the mother and in company of feminine figures. We still see this today in most all cases where a male identifies as homosexual, and again, research supports that it's not an elusive inheritable gene, but instead, a learned state. To state otherwise is short sighted and quite small minded.

Race did not appear to reveal any trends. Surely, mongoloids and south east asians should contain the highest prevalence (in conjunction with their feminine appearance) if any. However, no such homosexual gene exists and their numbers are identical to all others.

There are a variety of journals in print and archives for further reading, many available in most university libraries and online for free. There is no excuse for ignorance, we're not living in the academic dark ages anymore.

Maybe Freud was right. All of us are born with the capacity(genetics)for homosexuality but environmental and other factors influence what we actually become.
The perfect combination of heredity and behaviorism!

So scientists don't even have proofs of a gay gen , but there are already studies and theories about what's the purpose of this fictional and hypothetical gene?

This only show what kind of society we are becoming, an overly tolerant society that accepts as naturals things without even making full investigations, just in the name of pleasure.

I have barely started digging into these kind of "investigations", but I already smell BS, all I can read, as far as I know and in a few words is: "There are not proofs that homosexuality is genetically developed, but we expect it to be the result of our investigations, so we are sticking to that because it's more convenient for society to not discriminate others, and also psychological and environmental factors are not considered to cause homosexuality because there are no further investigations about it, but we are not going to investigate it because it's not what we want the truth to be pointed towards"

Even if homosexuality is a choice people should be allowed to do what they want. There is no 'threat' to society and the comment above about STI's and AIDS is just ludicrous.

People, men and women, enjoy sex. That is all there is to it.

If left to their own devices and not suppressed by religious extremism and mental people, people are attracted to all different types of people. I don't believe there is a gay gene and even if it is a choice it is still 'natural'. If you want to argue what natural means I am all ears.

According to the original Scriptures of the Tanakh in Hebrew, Homosexuality is a man-made disease secretly engineered and secretly enforced by ancient royal and religious authorities...
Deep and dark are the motivations behind sexual disorder, at the very base of all disorders...

If at the core of evolution we believe that external forces caused biological mutations, why has not t he question been raised as to wether behavior can alter biology ? Becuase if this is possible, the argument that homosexuality is a man made phenomenon would have to be invstigated. We have discovered the gene for many anomalies in DNA that were altered by humanity. Just a thought !!

All theories are bias in that it assumes there is an evolutionary explanation for homosexuality. I haven't seen any evidence to rule out that it's simply a disorder. Is there an evolutionary explanation for pedophiles? Or autism? Or foot fetishes? There was once a psychological consensus that homosexuality was a psychological disorder, but now that it's not politically correct, they completely flip this consensus without any evidence whatsoever?