The Evolutionary Purpose of Male Homosexuality

A recent show on the science channel alerted me to an interesting new hypothesis about the evolution of homosexuality. Contrary to popular thought, it does not appear to be an accident. (If anyone can find documentation about this new hypothesis... let me know). Particularly interesting is the behavior of primate males in family groups. As is well known, apes (such as chimanzees, bonobos, and gorillas) that live in family groups consist of many females, one dominant male that gets exclusive access to mating with the females, and sometimes one or more submissive males that do not have the right to mate with the females. A new scientific hypothesis suggests that our early ancestors (who may have lived in similar family groups) may have developed homosexuality among these "submissive" males. The sexual behavior of the apes currently being studied suggests that male homosexuality has an important evolutionary advantage in family groups. The submissive males engage in homosexual behavior as a way to satisfy sexual instincts... but the advantage goes further than that. By engaging in homosexuality, the submissive males present themselves as no threat to the dominate male and thus promote group harmony, by discouraging male fighting over mates. Furthermore, these homosexual males provided survival advantages to the family group by helping to protect the females and infants from predators and rival family groups and to find food for the group. In this case, the sacrifice of the genetic survival of one individual gave an enormous advantage to the survival of the group. - Which is something evolution has been known to favor.

Although this particular advantage of homosexuality is obsolete for humans, the homosexual orientation would have survived despite that because our society changes far faster than evolution.

So.. for any homophobes that claim homosexuality is "unnatural" - Au Contraire! It is VERY natural, for some people!

Views: 3704

Tags: Science, biology, evolution, gay rights, homophobia, religion

Comment by archaeopteryx on March 18, 2012 at 2:44pm

But I think you're missing my point Sky,  or maybe I wasn't very clear inn the first place - if "gayness" is genetic, i.e., if there is a "gay" gene, how would it get passed on in the first place? Is it recessive (obviously, if it were dominant, the bearer would be gay and unlikely to pass it on), or recessive, in which case, it would take the meeting of two such recessive genes to create a "gay" person? If the latter were the case, wouldn't - according to Mendel's Laws of Heredity - there be a 25/75 ratio of gays to straights? (I use the two terms because they take up less space to type)

Understand we're not debating here, I'm genuinely curious.

Comment by kris feenstra on March 18, 2012 at 3:28pm

according to Mendel's Laws of Heredity - there be a 25/75 ratio of gays to straights? (I use the two terms because they take up less space to type)

Setting homosexuality aside for a moment, what you wrote is grossly inadequate when discussing genetics.  There are more variations that could conceivably be at play than I care to list, some of which are covered in entry level genetics units (such as multi-allelic traits, polygenic traits, and traits with multiple phenotypes).  While I'm not suggesting that homosexuality fits any of those categories (if it even is genetic in part or in while), when there are som any unknowns, conversations on genetics cannot be limited to such simple inheritance.

Comment by Arcus on March 18, 2012 at 4:30pm

@arch: It seems to be a mixture between biological predispositions and environmental factors. There was a fairly widely reported and comprehensive Swedish twin study which has now been added to Wiki:

A 2010 study of all adult twins in Sweden (more than 7,600 twins) found that same-sex behavior was explained by both heritable factors and individual-specific environmental sources (such as prenatal environment, experience with illness and trauma, as well as peer groups, and sexual experiences), while influences of shared-environment variables such as familial environment and societal attitudes had a weaker, but significant effect. Women showed a statistically non-significant trend to weaker influence of hereditary effects, while men showed no effect of shared environmental effects. The use of all adult twins in Sweden was designed to address the criticism of volunteer studies, in which a potential bias towards participation by gay twin may influence the results (see below).

Overall, the environment shared by twins (including familial and societal attitudes) explained 0–17% of the choice of sexual partner, genetic factors 18–39% and the unique environment 61–66%.

Comment by archaeopteryx on March 18, 2012 at 4:54pm

@ Kris - RE: "what you wrote is grossly inadequate when discussing genetics" - which is why, in both my posts on the subject, I indicated I was seeking information, rather than making definitive statements.

@Arcus - In a much earlier post on a different forum, in a similar discussion, I quoted my high school science teacher, who said that in an investigation of any physical condition, one could never entirely separate heredity from environment. My premise was shot down in favor of a strictly genetic explanation.

Comment by Arcus on March 18, 2012 at 5:21pm

@arch: By me? In that case I have not made myself entirely clear, as my opinion is that it is a mixture, though with the environment as the main factor. I usually get blasted since that position apparently implies that it would a conscious choice. A choice perhaps, but not conscious.

Comment by archaeopteryx on March 18, 2012 at 6:43pm

No Arcus - it happened a couple of months ago, and I honestly don't recall by whom. But definitely not you.

Comment by Daniel Pereira on November 19, 2013 at 1:16am

I think this is flawed because it wouldn't correlate to female homosexuality. Also if it was true then all males who failed the mating game would turn homosexual, not just a few. If some submissive males can remain hetero, then all males would stay hetero because evolution only makes changes that are necessary to survival. If it isn't necessary for all submissive males to become homosexual then why would it be necessary for a select few to become homosexual?

Here is a link to a site with other ideas about why homosexuality may have occurred:

Comment by Cara Coleen on November 19, 2013 at 12:06pm

evolution only makes changes that are necessary to survival.

This is incorrect. Evolution isn't a process with a purpose. Evolution is simply changes, or mutations, in organisms that may or may not lend to the survival of the organism. There's no "purpose" in the changes. Of course, with every cause, there is an effect... but the effect is incidental. This is one of the main misunderstandings of evolution: that it is guided, or that it has a purpose. It does not. Evolution is not a progression to something better or more likely to survive. Many times evolution causes changes that lead to death or disadvantage. What happens is that those changes make the organism unable to procreate and pass along the trait that put them at a disadvantage... but not always, which is the reason so many "bad" traits continue to get passed on.

Females can be impregnated whether they are heterosexual or homosexual. Most female sexuality is somewhat fluid anyway. Sexuality in general is more of a gradient instead of black and white, straight vs gay. It is hard to "breed out" sexual attraction when it's such a mixed bag. Many, many people have produced offspring despite their attraction to the same sex. It hasn't been until recently that women have even had the option of rejecting men as partners. And parents are not just passing their own sexuality to their offspring: they are passing thousands of generations of sexuality to their offspring.

Evolution happens slowly. I doubt that homosexuality has been enough of an advantage or disadvantage to be affected one way or another. Even if a culture decides to kill off homosexuals, they will not succeed because those with homosexual tendencies will simply suppress their desires and go "in the closet". Besides, it's not just homosexuals who carry the "gene". It's just there, and I think it always has been. It doesn't have to serve a functional purpose. That's not what evolution is.

Comment by Warren on November 19, 2013 at 12:41pm

Evolution is a series of random mutations over time over generations, most are harmless, some don't work out at all, and some benefit the animal or even plant that makes it more competitive in it's environment. Evolution mostly takes a lot of time, but not always. We can even see it in our lifetime. Case in point over crabs in Japan. There is a crab in Japan that the carapace looks like a Samurai warrior. It wasn't always like that, when Japanese fisherman saw a crab that they caught looked a bit like a Samurai face, they threw it back, sort of encouraging that design of crab carapace to the point that it is not unusual to find that "mutation" catching that kind of crab there. It happens, quicker than you think. Esp with microorganisms and viruses, which mutate often and go by the same rules of some become more competitive.

Comment by Daniel Pereira on November 20, 2013 at 6:37am

Cara I'm sure everything in evolution has a purpose, otherwise it would make no sense for evolution to occur. I'm pretty sure homosexuality has a purpose. I just don't think the purpose outlined in this blog adds up. It doesn't explain the existence of female homosexuality either.


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