Azlana

I had actually read somewhere that there was a species of frog in Australia I believe, that would only have male offspring for short bursts of time, and that those male frogs would be mates for life, but obviously not be able to reproduce, so as to control the population. Might have actually been on Animal Planet or some program like that.

Dr Rick

AAAS:

...Homosexual behavior is common but unexplained by Darwin. Over 300 vertebrates, including monkeys, flamingoes and male sheep, practice homosexual behavior...In female Japanese macaques, homosexual behavior appears to have evolved from female strategies to coerce reticent males to mate with them. Eager females will mount unwilling males and prompt them to mate with them - a strategy that was easily expanded to mounting other females. Despite these evolutionary origins, however, homosexual behavior among Japanese macaques may have no adaptive value.

...Vasey agrees, however, that something has to give: ''What I'm seeing, in my one species [macaques], is an unbelievable amount of sexual diversity that is very common. I see it every day, and traditional evolutionary theories for sexual behavior are inadequate and impoverished to account for what is going on.''

Rick

Paul2

why?

Doubting Didymus

Because PZ doesn't agree with it, of course!

Seriously though, knowing the hypothesis you're talking about as I do (though I can not remember the source either) I can say that it is an extremely tenuous idea. It goes something like so: Genes that influence organisms towards becomeing non-breeding individuals that are a benifit to their close relatives (by helping out in any number of ways) can be selected for as if by proxy. If an individual houses a gene for sterility + helpfulness then it is likely that that genes close relatives will also have the gene. By being a benifit to the nearby individuals with the gene but without competing for breeding rights or increasing the population, it is ensuring that copies of itself make it to the next generation, not through the sterile individual, but through the related individuals who are likely to share the gene, but are not sterile.

The idea is that homosexuals may house such a set of genes, and they persists because homosexuals are a benifit to the close relatives, without increasing the population. This idea relies on a few things:

First, that homosexuals do not breed. This is widely accepted as obvious, but in fact it is far from definite, as PZ has pointed out. In fact, 'strong' homosexuality (homosexuals who completely shun sexual contact with the opposite sex) are representitive of only one end of a wide spectrum of sexualities. If the sterile helper hypothesis were true, a more exclusive on/off would be more expected.

Second, this hypothesis does not explain homosexuality, only sterility. It is not obvious that the genes responsible for the phenomenon should swing sexuality across the gender divide instead of simply removing it. Sterility is not a difficult thing to come by.

Third, this is a gene-centric 'selfish replicator' concept. While I am a gene centrist to the core of my black heart, it can only be applied to those biological phenomena that are influenced in some way by the organisms genes. For me to believe that homosexuality evolved as ANY kind of adaptation I require evidence that it is related to genetics. Without that link, a trait can not be copied to the next generation with fidelity, and thus can NOT be selected for. I have not yet seen any convincing evidence that homosexuality is genetic.

Given these objections, I can not accept the hypothesis. Also, given objection three most specifically, I can not accept any evolutionary explainations of homosexuality of any kind, unless a genetic relationship is uncovered.

pz

Shouldn't that reason be more than sufficient?

Actually, my main objection was that it would develop to "curb overpopulation". It would be kind of an odd evolutionary strategy: there are too many of us voles/aphids/gosbeaks/whatever to be supported by our environment, so I'll pass genes on to my children that make them inefficient reproducers. Yeah, like that'll work.

Now if you wanted to argue that a good evolutionary strategy would be to make my male children excessively hetero, hyper-aggressive macho guys who kill all their competitors in testosterone-addled tantrums, that might be a better way to curb overpopulation. Successful evolutionary strategies generally increase your rate of reproduction at the expense of the other guy's, not vice versa.

Dr.GH

God gave men nipples so that they can have something to play with for their other hand.

Doubting Didymus

I think the idea is less silly that that. If (purely hypthetically) you could somehow manage to get half your offspring to be breeders, and the other half to be sterile but extremely helpful to the breeding offspring, then your breeders might get an advantage over similar families in which everyone competes for the same reproductive opportunity.

This is not really 'curbing' the population as a whole, but locally its going to function to keep the breeding population down. Those individuals trying for the more standard strategy of having lots of competitors in the breeding wars might be ad a disadvantage over those who invest in only a few breeders, and supply them with sterile servant sibling to boost their chances. In other words, choosing a small number of offspring with very high chances of replication might win over having many offspring with dimmer prospects. We already see this in species that invest a lot of resources in a small number of huge needy breeding males, as opposed to those that invest in many males. Sterile helpers is just another way of doing a similar thing. It's not so much about the curbing of population, but about reducing the amount of competition your offspring will encounter.

However, theoretically possible /= historically probable.

Paul2

Thank's for the info, that makes sense.

Doubting Didymus

We live only to serve.

AmericanHeretic

I'll share a theory on how homosexuality may be an adaptive switch that selects for stress and influences local as well as general population growth rates accordingly.

First I'll remove the direct individual-based genetic argument.
If homosexuality is directly genetic, this is perplexing. If this is the case, and given the historical pressures (i.e. murdering of homosexuals in centuries past) in addition to the obvious fact they breed a great deal less, the genetic pathway to sustained 10% population levels, as we see among homosexual humans, could not stay constant, as it does. Animals show homosexual behavior and did not face the more difficult selection pressures mentioned here, yet ratios among them remain just as constant as they do among human populations. I think this effectively erases the genetic argument as to homosexual causation and implies another completely different mechanism that is not genetically handed down by homosexual individuals, but rather, is built into the breeding mechanism itself and serves a clear beneficial purpose.

My theory:

All humans begin as females in the womb. (This explains why males have nipples, incidentally.) In the first trimester, male embryos receive their first issuance of testosterone and soon thereafter male genitalia appear. In the third trimester, the male fetus recieves another issuance of testosterone and no further physical changes are observed. It is suspected that this third-trimester male hormonal issuance is to create brain changes that change the brain from female to male.

Gay men have lesser hippocampus region brain development than nongay men. A recent study of gay sheep indicated this.
A famous study of males born in Germany just after the end of WWII showed markedly higher rates of male homosexuality in the babies born in that timeframe. The suspected cause was severe maternal stress, which blocked third trimester hormonal issuance, thereby creating gay male offspring in higher numbers than is the normal rate of 10%.

The evolutionary advantage to this mechanism, which is a switch of sorts I think, is that in times of maternally experienced severe stress, less breeding males are born. An increase in non-breeding male birthrates would act to slowly ease environmental carrying capacity issues and thereby increase chances for group survival over a multi-generational span. Collective food production systems among humans, and the food supplies of various animals, remained relatively steady for enormous periods of time, so this homosexual-ratio breeding rate adjustment mechanism would slowly act upon struggling populations until such time as the population based stress source abated. This was evolution's means of determining if a group or species was nearing a situation where survival was being impaired by simply too much breeding and lesser population growth would enhance group survival odds. This then, was accomplished in a less severe than "survival of the fittest" individual method (where mass die-offs would occur), but rather, a "more versus less stressed" breeding rate based collective method triggered by the status of breeding mothers, of most species.

I think evolution has a random aspect, but it is surely relative to the environment, so while blind in way, it is also effective at developing means that work respective to the survival variables a given population faced. The eye was inevitable, so was the use of sound, fins, legs and wings as well. So why not a sexuality-based breeding-rate switch that can be tripped in times of stress among a species or local group? In other words, individual survival is one aspect of evolution, of course, but, group survival is equally selected for, perhaps more subtley and less well understood.

If this theory is correct, then gayness is literally something we evolved to live with and these people are very much a part of why we are the way we are and why we survived. In no way whatsoever is it acceptable to be prejudiced towards them, especially in light of the fact that they are here to help adjust the birth rates such that we all have better survival odds.

Interesting stuff is it not?