[Greta Christina] Why Did Gayness Evolve?
So why, from an evolutionary perspective, are there gay people at all?
In my last column, I speculated wildly on the question of why there are so few people who are equally attracted to both women and men; why the distribution of human sexual orientation tends to clump into “more or less heterosexual” and “more or less homosexual” camps. But this intriguing and currently unanswered question begs a much larger, even more intriguing question:
Why — from an evolutionary perspective — are there gay people at all?
Current research seems to be suggesting that homosexuality is a trait people are born with. At least partly, if not mostly or entirely. The jury is still out, but that’s the direction the evidence is currently pointing to. And while it’s possible that gayness is inborn but not genetic — it could be caused by in-utero environmental factors, for instance — it’s looking like genetics are, at the very least, a significant part of the picture.
But when you accept the idea that homosexuality is genetically wired, you get faced with a very puzzling question:
Why would that be?
Why, from an evolutionary perspective, would a not-insignificant number of us have been born wanting to boff people we have zero chance of reproducing with?
Why wouldn’t that trait have been selected out long ago?
There are lots of hypotheses as to why this might be. I’m not going to argue for or against any of them here (if for no other reason, it would make this piece way too long). Instead, I want to point a very important and often overlooked fact about evolution:
To ask “What is the evolutionary reason for (X)? Why did (X) evolve?” is often the entirely wrong question.
There are many, many traits of humans and other living things that are incidental by-products of evolution. They’re not the traits that were selected for. They’re incidental by-products of the traits that were selected for.
Let me give an example. Let’s ask the question, “Why did bones evolve to be white? What is the selective advantage of bones being white?”
As you can probably guess, this is a completely misleading and even silly question. There is no selective advantage whatsoever of bones being white. Bones could be hot pink with zebra stripes for all evolution cares. Bones are white because, due to an assortment of evolutionary pressures and accidents, bones are made of calcium — and calcium is white. The fact that bones are white is an incidental by-product of the fact that they’re made of calcium.
Or, to bring it back to the more interesting topic of sex: Let’s look at the question, “Why do men have nipples?” There is no selective advantage to men having nipples. There is, however, an obvious selective advantage to women having nipples, what with keeping offspring alive and all. And there’s a selective advantage to having women and men grow with the same basic blueprint, with only relatively minor differences. So women and men are both born with nipples . . . nipples that develop in women to serve an important function, and that in men exist only for, shall we say, entertainment.
And it’s been suggested — controversially, but with good evidence to back it up — that the female orgasm works this way as well. According to this hypothesis, there’s no evolutionary reason for women to have orgasms; they play no significant role in our survival or reproduction. (The fact that many women have orgasms so unreliably, and with such difficulty, and that a good number of us don’t have them at all until later in life and in some cases not at all, is some of the strongest evidence for this.) Female orgasms are like male nipples: women have orgasms because men have orgasms, and women’s and men’s biological blueprints are similar enough that a reproductively useful function in one may still be present in the other even if it serves no evolutionary purpose.
Now, whether or not you agree about female orgasm, the general principle applies: Not every trait — not even every trait that’s passed on genetically — has been selected for by the process of evolution. Some are incidental by-products of the traits that were selected for.
And homosexuality could easily be one of these.
There’s a concept in architecture (stay with me, I promise this isn’t a tangent) that’s been swiped by evolutionary biologists — the concept of the spandrel. In architecture, a spandrel is the triangular space under a staircase (or a similar space between two arches). And obviously, it isn’t something an architect will intentionally design. An architect may try to design a staircase so the spandrel is attractive, or so it impinges on the space as little as possible. She may even try to make the spandrel useful (as storage space, for instance). But the spandrel is not the thing that was intended. The staircase is the thing that was intended. The spandrel is only there because the staircase is there . . . and because, with a very few exceptions (such as a spiral staircase), you can’t have a staircase without a spandrel.
Evolutionary biologists have swiped this concept for obvious reasons. There’s no design or intention in evolution, obviously. But the principle is the same: a useful feature with positive benefits will sometimes carry an incidental side effect, a feature that doesn’t have any advantages in itself but that has to be there for the selected feature to exist.
So even if homosexuality is inborn — even if it’s genetic — it may not be the trait being selected for.
Homosexuality may be a spandrel.
It’s possible that there is a positive evolutionary benefit in some people being gay. Some scientists have suggested that there is. But it’s also possible that being gay is an incidental by-product of some other adaptive trait that we need to survive and reproduce. It could be, for instance, that a preference for boffing women (or men) is inborn . . . and that it’s evolutionarily more advantageous for that preference to occasionally show up as same-sex desire than for it to never show up at all. Or the reverse could be true: it could be that in humans and some other animals (homosexual behavior is hardly limited to the human species), there’s an advantage to having our “identify someone you can reproduce with” wiring being more — oh, let’s not say “promiscuous,’ instead let’s say “broad.” With this evolutionary strategy, we may have a lot of sex that doesn’t result in successful reproduction . . . but the chance that we’ll reproduce with somebody becomes rather higher.
I’m not going to speculate on the likelihood of any of these specific hypotheses. I just think it’s important to remember the general principle: Not every trait serves an evolutionary purpose of survival or reproduction. Some are incidental, spandrels. Homosexuality would seem like an odd trait to have evolved, something of a barrier to reproduction that needs some serious explaining . . . but that doesn’t mean the explanation is, “Homosexuality serves (X) purpose.” The explanation could be, “(Y) serves (X) purpose . . . and homosexuality is connected in some way with (Y).”
And I think it’s important to remember this as well:
Homosexuality isn’t as much of a barrier to reproduction as people often think.
Very, very few people are entirely, 100% homosexual. Just like very, very few people are entirely, 100% heterosexual. Our behavior tends to slant more or less in these two directions, possibly due to social constraints as much as natural ones . . . but most people have the capacity to be sexually involved with both/ all genders, at least to some degree. So while homosexuality may seem like kind of a weird trait from an evolutionary standpoint, it’s really not. Unless you’re a 100% completely same-sex oriented Kinsey 6 type gay person, homosexuality is only a moderate liability in the Evolutionary Sweepstakes. (Speaking for myself: Effective modern birth control is way more of a factor in my not reproducing than being a dyke.)
Finally, I want to say this:
I know some gay people won’t like this idea one bit. Some gay people won’t like the idea of gayness being an evolutionary accident or afterthought. To them, I want to say two things.
First: We can’t reject scientific hypotheses simply because we don’t like them. That’s exactly what the homophobic religious right does: they reject the extensive evidence that queers are healthy, stable, responsible contributors to society and family, purely because it doesn’t fit their worldview. If we’re going to demand that they accept reality as it is, then we don’t get to reject reality (or possible hypotheses about reality) just because we don’t like it. There are some good arguments against the spandrel hypothesis of homosexuality . . . but “it isn’t nice to gay people” is not one of them.
Second: If we are an evolutionary spandrel . . . there’s a serious upside.
And that’s that we’re not going anywhere.
If homosexuality is an independent trait that has been selected for (or not selected against) due to some reason of its own . . . it could eventually be selected out. It does confer some selective disadvantage, after all, if not a massive one . . . and as society becomes more gay-accepting and more people are comfortable with entirely same-sex oriented sex lives, that disadvantage only gets more pronounced.
But if homosexuality is a spandrel — an incidental by-product of evolution, hitching a ride on some useful and important trait that our species needs to survive and reproduce — it’s a lot more likely to stick around.
And I, for one, am in favor of us sticking around.
This entry was posted on Friday, 11 December 2009 at 8:31 pm and is filed under Culture. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
on Saturday, 12 December 2009 at 12:28 am Brook M. wrote:
As an evolutionary biologist, I have to disagree with your conclusion. A trait that is a ’spandrel’ (i.e. has not evolved directly from positive selection but instead is a side effect of some other trait that has) is no less likely to disappear during evolution than a trait that is not. The relative likelihood of either type of trait being lost through natural selection depends on the evolutionary context and the traits themselves. It is also possible that selection may act to decouple a ’spandrel’ with negative fitness effects from the trait that is under positive selection, so that the ’spandrel’ and its negative effects may be lost without losing the positive trait. In your analogy, this would be like evolving a spiral staircase in a case where there was some disadvantage to having a real spandrel.
In any case, I don’t think people should worry about whether their traits evolved through positive selection or come along with other traits–regardless of how we got them, there is an evolutionary reason for having those traits. The problem comes when we attach a moral judgment to natural selection–traits with positive fitness effects = good, all other traits = bad–especially because we don’t generally think of fitness in the evolutionary sense as a moral good (i.e. people with more children are better people). The ‘why’ of any trait is important in understanding our history, but we shouldn’t be constrained by that ‘why’ when making decisions about what is a ‘good’ or ‘not good’ trait.
on Saturday, 12 December 2009 at 6:51 am Joel Monka wrote:
I think your theory about the advantages of a broad range of attraction makes a lot of sense. There would be a tremendous advantage for a tendency for hybrids- inbred species start showing all kinds of defects. Many times, there are potentially fertile crosses between breeds that look so dissimilar that to the naked eye, they might as well be different species- look how different two types of dogs can be, for example. So the innate attraction must be a balance between the exotic and the familiar, with very broad parameters.
on Monday, 14 December 2009 at 1:54 pm Greta Christina wrote:
“As an evolutionary biologist, I have to disagree with your conclusion. A trait that is a ’spandrel’ (i.e. has not evolved directly from positive selection but instead is a side effect of some other trait that has) is no less likely to disappear during evolution than a trait that is not.”
Good to know, Brook. I wasn’t aware of that. Thanks for the correction!
on Monday, 14 December 2009 at 2:24 pm Blake Stacey wrote:
Where else do we keep young wizards?
Assuming it is developmentally possible to decouple the traits.
on Monday, 14 December 2009 at 4:09 pm Kiwiwit wrote:
Excellent blog. I have a theory that the impact of birth control, in-vitro fertilisation and other medical advances, combined with social trends, will see (and already is seeing) an explosion of ‘non-standard’ human family and reproduction models that will dramatically change human society. In my view, this will be a very good thing. Vive la difference!
on Monday, 14 December 2009 at 5:58 pm Valhar2000 wrote:
Why is this?
I’ve heard this sort of sentiment before, and it doesn’t make much sense to me, although perhaps there is more to it than meets my eye.
What I mean is that, inasmuch as being gay is something inborn, and not a choice or something that has to be created, it is not something that one can be proud of, since it is not an accomplishment. It doesn’t make anymore sense to me to be proud of being gay than it does to be proud of being white, or to be proud of having 2 arms and 2 legs.
I suppose that the unstated meaning of this phrase in many situations is that one is proud of having had the courage not to hide, but rather to stand for what one thinks is right, and this is an accomplishment and therefore something to be proud of.
However, this source of pride is not unique to being gay, so if, for whatever reason, homosexuality came into decline, we should not expect this sort of sentiment to die out, and should therefore have nothing to mourn. The mere fact of the existence of homosexuality is morally neutral, and its value is symbolic, rather than intrinsic. Returning to my first analogy, if bipedalism gave way to tripedalism we could be just as proud of standing up for our right to have 3 legs, or 4 or 5, as we could be of standing up for our right to have 2.
Finally, I want to clearly state that I do not object to homosexuality in any way, nor do I object to people who take pride in it, nor I do I think its extinction by natural means, if possible, is desirable: as I say, its mere existence is morally neutral.
on Monday, 14 December 2009 at 6:28 pm Greta Christina wrote:
Valhar2000: That statement didn’t have anything to do with pride in being queer. I am proud of being queer, but it is the other sort of pride you describe — pride in having weathered society’s hatred and come out stronger, pride in coming out despite the pressure to stay closeted, pride in how far our community has come and how much we’ve accomplished in just my lifetime, etc.
What I said was “I am in favor of us sticking around.” I think queerness has a positive effect on society. (Completely separate from the possible evolutionary benefits of homo- and bi-sexuality.) I think our presence has challenged society to rethink rigid gender roles, how we define marriage and family, and a whole host of other concepts — in ways that, on the whole, I think have been very much beneficial. It would make me sad to think that in a few hundred or thousand years, queers might select ourselves out of the gene pool. I hope that doesn’t happen. Society would be flatter and sadder if it did.
on Monday, 14 December 2009 at 7:54 pm jemand wrote:
“If we’re going to demand that they accept reality as it is, then we don’t get to reject reality (or possible hypotheses about reality) just because we don’t like it.”
Yes, BUT, hypotheses which *on their own and as an idea* have negative influences on society, AND have little to no evidence in their favor, much less anything remotely approaching “conclusive” OUGHT to be shelved until such time that society changes such that the idea on it’s own as an idea doesn’t have that negative effect anymore.
This may or may not be in that category, but that category *does exist* and delaying investigation to a point where more conclusive research can be done in order to avoid having partial or badly done research support an ethically negative social order, is not at all a rejection of reality, but rather an acceptance of the whole of reality, including society and the wellbeing of the individuals in it.
on Monday, 14 December 2009 at 8:13 pm Vene wrote:
I was really hoping that this was going to be mentioned
http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0002282
Basically, that male homosexuality exists because the same genes have an positive effect on female fertility.
on Tuesday, 15 December 2009 at 12:14 am Ola wrote:
Vene, you beat me to it by an hour! :-) Yes, I’m sure Greta will be happy to see her hypothesis shared by some scientists and supported by interesting evidence.
on Tuesday, 15 December 2009 at 4:07 am Valhar2000 wrote:
Okay. Thank you, Greta.
on Tuesday, 15 December 2009 at 10:18 am Rosie Redfield wrote:
Brook M’s comment about spandrels being no more stable than selected features is true, but I think Greta’s original point about the evolutionary stability of a gayness spandrel is also valid.
A spandrel is indeed no more stable than the selected feature that it’s a side effect of. Thus if gayness is a spandrel of selection for human reproduction, it’s no more stable than reproduction. But reproduction is the most stable (the most strongly selected) of all evolutionary traits; if we lose that, we go extinct. The staircase example fits - staircase spandrels are stable because we continue to need staircases.
on Tuesday, 15 December 2009 at 1:39 pm Kagehi wrote:
There was a study done on deer populations a while back and may present a hypothesis. They found that breeding success was greatest between females with high levels of female characteristics, including low aggression, and males with high levels of male traits, such as aggression towards rivals. The problem is, the genetics for those traits are not relegated to either the male or female chromosome path. They are scattered enough across the whole range of genes that you can end up with females with high male aggression and size, which breed very poorly, and males with high levels of females traits, who breed poorly, or not at all. Due to the cross over of these traits, and the constant trade off of mutant versions of them, its not possible to have perfect females **and** perfect males. Such things are actually as much aberrations in the species as males that are high female traits, and females with high male traits. But, in order to maximize success, the majority of the population **has to be** fairly similar size, fairly aggressive in the males, and fairly non-aggressive in the females, and thus likely to breed at all.
Now, with humans, there is an added level of complication. Our closest relatives also use sexuality as a trade commodity, and socialization as a way to bind groups together more cohesively. So, you not only, likely, need the same trade offs with aggression vs. passivity, and size differences, but you *also* need a greater malleability, with respect to sexual expression in general. And, that is bound to create a bit bigger wobble in the system of balances than plain sex for breeding already generates in some species, like deer. In effect, to have two sexes, you either need a **lot** more stuff in the selective clump of genes, which may not be practical, given how it arose, or you naturally end up with wobbles in the system, which only normalize statistically, due to the genes for the *stable* configuration passing that on more than the unstable ones.
on Tuesday, 15 December 2009 at 2:53 pm David Harmon wrote:
Indeed, spandrels in general are no more stable than selected features, but once established, they may prove “useful”, and thus be recruited for further selection. The wide prevalence of “homosexual” behaviors throughout not only mammals, but birds (I’m not sure about other vertebrates), suggests that same-sex attraction is heavily co-opted for social purposes.
on Tuesday, 15 December 2009 at 6:55 pm MattK wrote:
This is my first time reading this blog. Great post.
jemand said:
I have a couple points to make about this. First is that science does not work when individual investigators hide data or hypotheses from each other for fear that they are controversial (partly because people often don’t appreciate weaknesses in their hypotheses until they have been exposed to criticism). Science also does not work by waiting for hypothesis to be ironclad before publishing. Darwin’s Origin was almost an exception and look what happened to him - he very nearly got scooped and even he had to collaborate with his colleagues to some extent. Also, it didn’t protect evolutionary biology from misunderstanding, denialism, and misuse even to the present day. Times are different now especially in the publish-or-perish short grant cycle where students who are only around for 2-4 years do most of the work. You want to tell a PhD student that they will be working on a project that will produce no publications even after they work for four years at 60 hrs per week with little pay and their career depends on their publication record? Third society will never be ready to handle anything profound that science has to offer about the nature of reality until they figure out how science works. Shielding them from science will not help that understanding.
I do sympathize with your point though. A little knowledge can be a dangerous thing (consider AIDS denialists and anti-vaxers) and bad studies don’t help anyone. Part of the problem is how bad the media is at relaying science and how bad people are at understanding it. A cool piece of research looking at effects of added testosterone on women’s behaviour is written up here. Briefly in a betting game involving fairness women were given a placebo or testosterone and were asked which one they thought they got. So there is two effects - the effect of testosterone and the effect of believing (or not) that testosterone has been administered. Two interesting things happened. 1 )The belief in testosterone had a stronger effect then actually getting testosterone did. 2) Women who thought they had testosterone played more aggressively because that is what they expected the effect of testosterone to have. But women who actually got testosterone tended to play more fairly and less aggressively. I think that this has major implications because it shows that perceptions of scientific information (the effect of testosterone) actually change how people experience the effects of the phenomenon in question. Consider how this might play out wrt evolutionary psychology and its hypotheses about human behaviour. I think a course on how to understand science and the media should be offered as part of high school curricula.
David Harmon said:
I don’t see how the wide prevalence itself suggests that at all any more than the prevalence of white bones suggests that bone whiteness has been co-opted for some function.
Kagehi, I like your example. One quibble is that inter-male aggression is not likely to have evolved to help the population. Aggressiveness in males has evolved to increase their individual fitness and probably actually hurts the population by decreasing effective population size. Antlers, for example, don’t actually help deer populations. They are very costly in resources (calcium for one) and probably also increase predation risk. What they do is allow male deer to compete against other male deer but this only helps the individual. If males cooperated and spent their energy helping their offspring then they would help the population but that is not what happens. In some places deer are hunted so heavily that many males fail to grow antlers at all. I don’t see how this hurts the population (the not growing antlers part, not the hunting bit). It just means that the balance between sexual selection and natural selection has shifted away from individuals deriving net fitness benefits from big racks (they impress the hunters more than the other deer I guess).
on Tuesday, 15 December 2009 at 9:33 pm Kagehi wrote:
Problem with your quibble MattK is that evolution is not about **individuals**, its about species. While its true that cooperation is helpful to species survival, it does nothing to weed out bad genes, and can even result in more unstable ones staying in the gene pool. This may be a must for species that have high adaptation needs, but is a disaster for ones that need a narrower set of characteristics. Basically, a cooperative population can take care of those that wouldn’t survive in a less cooperative one. You have a trade off in the system. However, one might note that, as cooperation grows, more “social” based dominance and pecking order sorting may be useful, and a sexual trait that *used to* only regulate a balance in aggressiveness, size, etc., may be coopted for other reasons.
Besides, as I said, **over aggression** in deer proved bad because females didn’t want to mate with them, and aggressive female deer would tend to try to fight would be mates. The edge cuts both ways, and still does, in a **cooperative** species.
In any case, just because some outside effect, like hunting of deer with large racks, may change the dynamic of *one* aspect of the system, it doesn’t follow that it effects *all* parts of it. Such aggression can be seen in horses, and other herd animals too, whether they have horns or not, so you might have an impact on sexual selection in the short term, based on one of the cues being fowled up, but in the long run, you have done far less than you imagined.
And remember, cooperative species are not, generally, endurance runners. They may want speed, smarts, skill, or any of a variety of other things, none of which necessarily require size, aggressiveness, or other traits. If you are the hunted, making sure your offspring can “outlast” the hunter, even if you can’t outrun them, may be more critical that being cooperative. There are a lot of variables.
on Wednesday, 16 December 2009 at 7:02 am MattK wrote:
Kadehi, other readers probably didn’t come here to read an argument about natural selection but I’m going to reply to this anyway.
Populations evolve, individuals do not but individuals (or genes) are the main units of selection (for good and more thorough explanations see The Selfish Gene by Richard Dawkins or The Red Queen by Matt Ridley). The males are acting in their individual interests and not that of their species. In Pumpkinseed sunfish there are satellite males, sneaker males, and dominant males. Dominant males are big and colourful. They build a nest, defend a territory, and display to attract females. Sneaker males are small and drab. They can’t defend a territory, instead they just sneak in and release sperm to fertilize the eggs in another male’s nest when he is trying to mate. Satellite males actual mimic the appearance and behaviour of females in order to trick the dominant male into letting them into the territory. They then sneak sperm in just as the sneakers do. Wood frogs have a similar trick in which some males do all the hard dangerous work of calling to attract females and then the satellites take advantage of his hard work. This makes no sense if, as you suggest, males compete so that bad genes can be weeded out for the good of the species.
About cooperation - lots of animals (and plants, fungi, and bacteria) cooperate. Vampire bats will regurgitate blood to feed other unrelated bats who were unable to find a blood meal and in danger of starving. The catch is that the receiver will have to return the favour later or the other bats will stop helping it. This is reciprocal altruism but it definitely doesn’t help weed out bad genes. Another example. Male lions (usually related individuals) will cooperate to take of prides. They then kill all the cubs which brings females into heat sooner and reduces competition for the males’ own cubs. How does this help the species?
on Wednesday, 16 December 2009 at 7:41 am Sebastian wrote:
My take on homosexuality (and other sexual “perversions” and deviations from the “mainstream”): It is not hereditary and it is has not evolved. It’s just a manifestation of the genetic composition of the gay individuals. And since we are all genetically unique and since there are so many of us, gayness is bound to emerge at some point in some individuals.
A fundamental requirement for evolution to be able to happen is that offspring deviate from their parents. This means that offspring are not straightforward clones of their parents, nor simply a “mix-n-match” of the parents’ genetic composition, but that mutations happen too which introduces variation and “new features” in the offspring which, if by chance are beneficial to the offspring, are then later selected for and spreading in later generations.
As genes control everything in our physical embodiment, this genetic variation of the offspring can occur in many forms and on many levels, with either major or minor implications for the offspring.
- Some are a bit taller than their parents, some are shorter.
- Some are hairier than others, some have less hair than others.
- Some are a bit more darker-skinned, some have lighter skin.
Etc… you probably all understand this.
But as genes control what we physically are, and as our brains are part of our physical bodies, and as our brains affect our personalities and preferences, our genes also determine what kind of persons we become:
- Some prefer sweet tastes, some bitter testes
- Some prefer to deliberate before they act, others jump right in and do things
- Some have much patience, some get enraged by the slightest obstacle
- Some prefer to do things with their right hand, some like use their left hand
- Some prefer sexually women, some men, some both.
In other words, gene variation is what makes us all unique and individuals. Physically, and by proxy, also mentally.
With regard to the above, I view the headline of the blog post “Why did gayness evolve?” to be very misleading. Homosexuality isn’t anything that evolves over time in a species, like for example in the way that wings evolve in a species over tens of thousands of years with each successive generation having more and more advantage and and better use of their longer and longer feathered extremities. There are no lineages of humans in which gayness is evolving or has evolved, dominating more and more the sexual preferences of that lineage. Homosexuality and other quirks of human sexuality are simply nature’s way of introducing variety into the gene pool, trying out new possible and possibly beneficial features, for every lineage of humans, in every generation. Every parent can get a gay child, whether the parents are gay or not.
(Argh… this text didn’t quite formulate my thoughts as clearly or as extensively as I would have wanted… but I think you got the gist of it… :) )
on Wednesday, 16 December 2009 at 10:45 am Reema wrote:
Assuming that we’re talking about an inheritable trait, isn’t the female orgasm evolutionarily advantageous, though? Aren’t women who have orgasms likely to have sex more often (and therefore reproduce more often) than women who don’t?
(Sorry, just skimming the comments for now; maybe I missed something.)
on Wednesday, 16 December 2009 at 12:45 pm MattK wrote:
Reema,
Probably not. In most mammals females never orgasm during copulation yet, where this has been checked (you don’t want to know), they are perfectly capable of having one. Do anorgasmic women have fewer children then orgasmic women? Probably not. But even if there is a fitness benefit from female orgasm in humans, the ability to orgasm would exist anyway, so it is not an adaptation.
Sebastian,
. How can it be genetic but not hereditary? That doesn’t seem to make sense.
You seem to be arguing that homosexuality is a product of certain gene combinations. The genes themselves are selected for but in certain combinations within some individuals they produce homosexuality. So you are arguing that it is a byproduct of genes that have other functions and a biproduct of selection for high levels of polymorphism at the relevant loci. Sounds kind of like a spandrel to me. Either way it is definitely a product of evolution. Not all of evolution is about natural selection (e.g. genetic drift) and not all evolved traits are selected for.
on Wednesday, 16 December 2009 at 7:26 pm Tim Evans wrote:
I mostly agree with Sebastian in that I’m not at all surprised that human populations exhibit significant variation in what appears to be a genetically-influenced characteristic (sexual preference). Like any other trait, genetic variation leads to phenotypic variation.
I’ll add to this a somewhat ironic wrinkle: a major source of the genetic variation that likely contributes to the spectrum of sexual preferences is recombination due to sexual reproduction. In other words, blame it on the straights!
on Wednesday, 16 December 2009 at 8:00 pm George Atkinson wrote:
There are good Darwinian reasons for the persistence of gay men in the population, according to
Proceedings of The Royal Society B: Biological Sciences
Evidence for maternally inherited factors favouring male homosexuality and promoting female fecundity by Dr F Corna, Dr A Camperio-Ciani and Dr C Capiluppi
Daughters of (at least some) gay men leave more offspring.
on Thursday, 17 December 2009 at 10:17 pm science_siren wrote:
As someone who works in the field of evolutionary psychology, there is the important point to make that homosexuality acts VERY differently in men and women. Having one adaptationist explanation (or one “spandrel”-style exaptation) still doesn’t do a very good job of explaining how homosexuality is expressed in men and women. Why is it so often that self-identified homosexual women have had a significant number of male partners and often don’t come out until much later in life, but the majority of self-identified homosexual males recognize their orientation very early on, and most do not engage in heterosexual sex? Why, on average, do homosexual women have LESS female partners than a comparable straight woman, and why do gay males have MORE partners than their straight male counterparts?
There is a lot of be said for the different cultural expectations regarding sex and sexuality for men and women, as well as the differing levels of encouragement to explore and identify sexual desires. Nuture certainly plays a role, but biology has helped form culture, and most certainly affects the development of homosexuality. How can one adaptationist explanantion account for both extremes of homosexual expression across the sexes? Lesbians seem more inclined to adopt the “extreme female” attitude, favoring fewer partners and long-term commitments, while gay men are more likely to follow the “extreme male” inclination, with more promiscuity and short-term pairings.
Of course, it has to be said that there are plenty of exceptions to these patterns (monagamous males and promiscuous females, etc), but the overall trends, which is what evolutionary theory looks at, are quite opposed. The evolutionary answers are far from being solved, but I’m inclined to think that the end result has to account for the differences between the sexes….I can’t wait until we find out more!
on Friday, 18 December 2009 at 12:12 pm Wholestyle on the Web: Week of 12/18/2009 | Bonne Vie wrote:
[…] Blowfish Blog: Why Did Gayness Evolve? A discussion of the evoluntionary benefits of homosexuality […]
on Sunday, 20 December 2009 at 2:27 am J wrote:
on Sunday, 20 December 2009 at 1:27 pm greensmile wrote:
avoiding the self destruction of internecine conflicts in a clan/family/tribe dependent creature like us talking apes would be a pretty valuable response for evolution to provide given the competitiveness of hetero males over women, territory etc.
that would explain why younger male siblings with slightly older brothers are more likely to be gay than others.
on Saturday, 26 December 2009 at 7:40 am Steve Law wrote:
The subtext here seems to be that homosexuality is defensible if it is based in biology/genes/adaptation/evolution.
But what if it’s not? (not genetic I mean)
Would that make it ok to persecute gays?
Of course not.
I look at human activity - art, music, sport, religion, science, sexuality, capitalism, crime, warfare… and while it’s possible to make up an evolutionary just-so story (social darwinism, sociobiology, evolutionary psychology, take your pick) about how our prehistoric ancestors might have found any of these activities adaptive, does that story really change anything about how we see their role in our lives now?
In short - does it matter whether homosexuality is ‘natural’ or not?
I’m as interested as anyone in what the evolutionary biologists come up with but let’s not use it to decide how we run our lives.
I have this scifi scenario I want to write where the GMO guys eradicate the ‘gay gene’ and discover to their horror that there are just as many homosexuals about as ever.
Happy New Year
on Saturday, 9 January 2010 at 10:00 am jenergy wrote:
the female orgasm question is tricky. i have read the stats that show women who DO orgasm don’t necessarily have more sex than women who don’t, but it’s been my experience that there are still some differences in the *way* different orgasming women have sex. personally, i do not “come easy” and have never been brought to orgasm by a lover. i have always gotten myself there, either before, during, or after. i’m aware that this does affect my sex life. i am not interested in one-night stands, or casual sex with people who i think won’t be willing to really “try” with me. i’m also aware that my inability (thus far) to orgasm “because of” a partner contributes to me becoming bored or disillusioned with partners and even sex in general. is this a bummer? yes. has it kept me from reproducing? well… no. but my baby, like many other American babies, wasn’t exactly planned. (and, if you’re wondering, i did not have an orgasm during the event in which she was conceived. c’est la vie.)
so, based on my own experience, i’m not sure i believe that norgasmia does not affect women’s sexuality… but it clearly does not affect women’s ability to conceive accidentally, which has been happening since the dawn of humanity. however, i do believe the female orgasm is evolutionarily important, as it — or the hope/chance of it — keeps women interested in sex. i think this theory is nigh indisputable, if you take into consideration the existence of one very amazing female body part: the clitoris.
on Wednesday, 3 February 2010 at 8:08 pm Steve wrote:
I’ve no evidence - not a sceric - other than my own sexuality and expirences.
I posit that the prevalence of homosexuality is simply due to the male sex drive.
Golden showers, leather, foot fetishes - I don’t believe that there is a strong case that can be made to argue that these have some sort of evolutionary basis other than the mind is a big and creative place and that the pressure of the male sex drive probably exaggerates a small fascination into something bigger.
Either way I’m annoyed that I’m not gay. I’m very jealous of my gay friends and the amount and varity of sex that they get compared to me - limited by my desire I only get to have sex with women, one at a time.
I tried to be gay. When I could not get sex from girls I would go to a gay club. Inevitably I would get taken home and the sex would be outrageous. A few times I even learned one of the guys names I jsut spent the night / morning with. There is nothing like that in the straight world. Nothing. Copious anonymous casual sex ….
If I had even the slightest physical attraction I would have identified as gay. As it was I would not describe myself as homosexual or hetrosexual - just sexual. I wonder how much homosexuality is homo and how much is simply sexuality looking for a place to play.