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bermanoid wrote: "You're invoking group selection here" ... "it's a classic prisoner's dilemma situation, and if you're going to take one lesson from Dawkins, it's that evolution always chooses to defect)" It's kin selection, not group selection. Consider Dawkins' "Twelve Misunderstandings of Kin Selection" wherein he writes: "To stick my neck out a little, it seems to me that, far from genes for altruistic behaviour being implausible, it may even be that a majority of behavioural mutations will turn out to be properly describable as either altruistic or selfish." ... "A gene for altruism, then, is any gene that, compared with its alleles, causes individuals to benefit other individuals at a cost to themselves." ... "But the kind of mutation that could lead to such altruistic restraint could be ludicrously simple. A genetic propensity to bad teeth might slow down the rate at which an individual could chew at the meat. The gene for bad teeth would be, in the full sense of the technical term, a gene for altruism, and it might indeed be favoured by kin selection." The example I gave seems perfectly aligned with this definition of altruism and kin selection. Indeed, it's a weaker but analogous form of what leads to eusociality. You say "it can't apply evolutionary pressure because it depends on the prevalence of the gene in other members of the population", .... and I think I understand why we disagree. I wrote "population" but sometimes meant "species population" and at other times meant "gene population." In an extreme hypothetical case, suppose that having a gay sibling help to raise a family meant a 5% improved chance that each child would live to adulthood and children in turn. Suppose also that having two gay siblings meant a -1% improved chance (perhaps because the person consumes more food, which could otherwise go to the children). Then there's strong kin selection here to have some, but not all, gay children. The descendants then become a larger part of the species population. In this case, I don't see how homosexuality would be a "reproductively negative trait" for the gene, only for some of the individuals carrying the gene. |
Personally, my suspicion is that homosexuality is more directly linked to a positive physical trait in the individual, though I don't have much to really back that up other than a vague sense that kin selection effects in evolution are rarely as strong as direct expressed ones. But yes, the "gay uncle" effect could explain it, too, and it's definitely an interesting enough phenomenon to be worth keeping in mind.
[1] In fact, I probably shouldn't react as negatively as I do against most invocations of the group selection argument, because oftentimes the points would be valid if expressed as kin selection arguments instead.