What is the Evolutionary Significance of Homosexuality?

Okay, right off I have to tell you, for the sake of this thread, you have to assume homosexuality came about because of evolution (I realize not everybody believes that–even those who support gays). That having been said, I think I will get the discussion started with my thoughts on the matter…

Yeah, I have been thinking about this alot lately. And here is what I have come up with: (a) Perhaps homosexuality is “recessive” gene. Alot of genetic aberrations (notice I avoid the term “disease”) are. Or…(b) Who says homosexuals don’t have children!!! In fact in the some ancient cultures like ancient Greece, women were just property and for making babies. Now of course women in the U.S. etc. are not property. But there is the possibility homosexuals do in fact want to have natural children of their own. And then they just have to find a willing (and hopefully not unsuspecting) woman. My next point is a little more complicated…

I have been thinking, who says homosexuals only get an advantage by mating? There are many “other” ways for homosexuals/gays to influence a gene pool. For example, many (probable) gays like Leonardo Da Vinci and Michelangelo influence society by their contributions to art and science. Indeed, they in many ways set the standards for male beauty at times. Maybe (and I realize I am going out on a limb here), they are subconsciously “directing” women to men with that (hypothetical) recessive gene I talked about above.

And yes, everything I just wrote applies to lesbians too:).

Those are my thoughts on the matter. What do the rest of you think?

And thank you in advance to all who reply:)

Weellll . . . Most bees and ants are sterile workers who never reproduce. But, as they’re all the queen’s sisters or daughters, they still serve the differential reproductive success of their genome.

For thousands of years most same sex oriented people did have children. And of course just a handfull of them a few thousand years ago would have dissembled those genes throughout the world.

Assuming there is only one cause of homosexuality and it’s genetic and it’s beneficial- there’s the “Good Uncle/Favorite Aunt” theory, which is that a segment of the population less inclined to reproduce provides more teachers who don’t mind working hours later than others or adult children who serve as full-time caregiver to their elderly parents or provide assistance (financial or otherwise) to siblings raising kids or whatever. Of course there are many exceptions to this- there are gays who couldn’t care less about helping others and there are plenty of straight people who have kids and still do fulltime caregiving to others and the like- BUT it is a potential advantage of gays to society.
(Personally I’m more of the “It’s just a quirk” like left-handedness or one blue/one brown eye theory.)

Since homosexuality only affects 1-5% of the population, it may not be a major evolutionary benefit. I have heard the same argument about mental illness. Some illnesses like bipolar or schizophrenia only affect 1-2% of the population. But depression affects closer to 10-20%. So the first 2 diseases can basically be explained as side effects of biology, whereas the depression may serve some biological function otherwise it wouldn’t be so common (then again, type II diabetes is common and it doesn’t serve a constructive function, however it is a byproduct of constructive functions like insulin resistance or the desire to eat high calorie foods and not exercise, which help avoid famine). So I don’t know if there is an evolutionary reason for homosexuality, or if it is just a trait we humans have. The point is, if homosexuality served a good evolutionary function, it might affect more than 2-3% of people and be closer to 10%+.

If there is an evolutionary reason, the explanation I’ve heard is that homosexuals do not have kids, so they can devote more time to their nieces and nephews, who share some of their genes and have higher survival odds.

As I keep pointing out whenever this topic comes up, to an evolutionary biologist, this really isn’t a big issue. There are zillions of ways in which alleles which don’t contribute to reproductive success can persist in a population. Just yesterday, I sat through a talk about sexual conflict in fruit fly evolution during which yet another explanatory idea was proposed. In a nutshell, it was about how really high fitness females tend to produce very successful daughters and less successful sons. Similarly, very high fitness males have great sons and not so great daughters (fertility-wise speaking). According to the speaker, there’s evidence that females relatives of gay men tend to be more fertile than average. Not much beyond speculation, of course, but the point is it’s really not difficult to think of ways in which homosexuality can arise and persist in a naturally evolving species.

I would view homosexuality for this a desire to have sex with a particular gender, which is a useful trait to ensure children, also a totally normal human characteristic, so the desire is within lines for human and for that matter animal behavior. But in this case the desire just somehow ended up in the opposite gender then what would produce the favorable outcome that it usually does.

This happens quite often where normally a desirable trait occasionally shows up in a undesirably way.

One take on it (sorry, behind The Economist’s pay wall)

Evolutionary biology.

But as mentioned, there are lots of things that persist that don’t convey an evolutionary advantage. Homosexuality may be one of them. Maybe it’s a common mutation like Downs syndrome. Maybe it has had little effect on reproductive success because it is culturally suppressed. Maybe there’s some truth to the Favorite Uncle idea posted earlier, althoug I have never seen much evidence of it in humans.

It’s funny how people start sounding like intelligent design proponents when the discussion turns to genetic influences on homosex.


Evolutionary divergence happen all the time and repeatedly - they are mostly essentially neutral. The ones that propagate broadly are considered evolutionary successes. Just because a divergence exists, and occurs repeatedly, does not equal evolutionary success (or significance).

I think a lot of human sexuality is based on using sex as a tool for socialization and bonding rather then for reproduction. Similarly, human females don’t “advertise” their fertility in the same manner other largish mammals do, they have orgasms similar to males and both genders engage in a lot of non-reproductive forms of sex.

So homosexuality is just another form of this, it allows same-gender pairs to experience sexual bonding in larger social groups, divorced from the original (and obviously still important) purpose.

Obviously, like most evolutionary psychology, thats more or less a guess, but I think there’s some evidence that suggests it. Most obviously, Bonobo chimps, who engage in homosexual (or at least bi-sexual) behavior and for whom sexuality in general pretty obviously serves as a social mechanism way beyond its reproductive function.

Couple things:

  1. We’ve done this at least half a dozen times in threads in GD and GQ, so I would suggest a search and reading what’s already been posted on the subject.

  2. Not everything has to give a reproductive advantage to survive as a trait-- it just has to not be too damaging to reproductive success. And behavior that is biologically determined does not have to be (directly) genetic.

Even with many homosexuals being culturally pushed towards having children with members of the opposite sex, and even assuming it’s a recessive gene, if that were all there was to it, one would still expect it to be a serious enough penalty to an individual’s reproductive success that it would be much, much rarer in the gene pool, if not completely eliminated. On the other hand, there are many different phenomena which might potentially be associated with homosexuality which could weigh against that. The difficulty isn’t in coming up with possible explanations, but in determining which of those possible explanations (which may be more than one of them) actually applies to humans.


While I think he could have phrased it better, Shodan’s point is clear. Evolutionary psychologists usually seem to assume that once they’ve proposed a possible competitive advantage for a certain gene, they’ve proved that the gene exists. Evolution, however, works by process of random genetic mutation. New genes are created by random mutations and then natural selection culls the harmful ones and propagates the useful ones. However, just because a certain theoretical gene is advantageous doesn’t mean that a mutation to produce that gene will ever arise. So, in short, those who think that genes must come into existence because they’re advantageous seem to be assuming that there’s an intelligent designer out there who’s guaranteed to create any imaginable gene that is advantageous.

Personally I don’t believe that homosexuality has a genetic basis or came about through evolution and I think the evolutionary advantages proposed in this thread are mostly pretty silly. But that’s just my opinion.

What evolutionary significance is myopia, sterility, baldness, a laughably small penis, autism, or any other seemingly less than optimal trait?

Evolution is the product of randomness. It’s not intelligent, it just tries random combinations of possible traits and hopes that one of them is an improvement. At least half of all people will be worse, in terms of survival fitness, than what the average level was of the previous generation – though ideally those ones will get killed off before they can breed.

There isn’t a Mother Nature who is carefully guiding the process along. Instead there’s a drunk redneck with a sawed-off shotgun splattering buckshot randomly all over the hell and hoping that one of the grains hits the target. The grand majority of everything, however, goes way off mark.

for bees at least, the matter is a bit more complex than that in that the genetic link between them can be even stronger than the “usual” parent/sibling bonds (link to video)

A genetic base, if strong enough (compared to whatever else may be “causing” homosexuality), is something that should be detectable. I’m not sure the evidence is conclusive in that regard, but I’m not ruling out the possibility.

In general though, I’d think that being exclusively homosexual puts the individual in an obvious evolutionary disadvantage. That, and the apparent fact that homosexual behavior (exclusive or not) isn’t all that uncommon amongst other animals may suggest that genetically determined homosexuality (if it exists at all) is a by-product of (a combination of) generally advantageous traits.

Just to make the point: occasional bum sex does not give individuals of our species a significant evolutionary disadvantage. We only need a few kids, but we like LOTS of sex.

There’s a whole host of things which can survive while being extremely disadvantageous to the individual. The easiest way to do that is to not even be genetic at all. Like many other problems, it could arise under certain conditions in the womb. Putting an embryo together is an incredibly complicated endeavor. Homosexuality could be a glitch in the translation or construction process. And since it would appear to be a not all too uncommon feature in many animal species, it’s probably a very persistent bug that would cost too much to rid from the ancient animal body plan (assuming it doesn’t turn out to have some hitherto undiscovered advantage).

I recently read an interesting piece in the NY Times magazine on gay animals (though the scientists quoted all stress that it would be unwise to apply some of their theories to humans, see quoted bit below).

The best evidence at the moment is that sexuality, like most complex traits, is a result of multiple genetic components as well as environmental factors.

That just moves the question up a level, though: If homosexuality is evolutionarily disadvantageous, then shouldn’t women evolve to not have those uterine conditions that lead to it?