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DanArmak comments on When does heritable low fitness need to be explained? - Less Wrong Discussion
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Is that really in need of an explanation, though? Some people are repulsed (by stuff), and others aren't. That is to say that whatever causes homosexuality probably doesn't also necessarily cause disgust for heterosexual activity.
Homosexuality could serve in such an instance to reduce competition, though. If you take animals such as lions, the males are extraordinarily competitive, to the point where they will kill children of other lions and drive away all competing males. Humans can't sustain that kind of competition, though. Humans are vulnerable for longer when we are children and require more investment to mature than most other mammals, so if competition is too fierce and leads to infanticide, the species can't sustain itself. In addition, humans are geared for cooperation with other humans, since we're naturally social creatures and capable of learning and imitation from others.
So I think humans don't really have much to gain from competition and more to gain from cooperation. And considering that, it might be the case that the "gay uncle" really does help the reproductive fitness of the group, or at least, doesn't hurt it so much that genes that create the potential for homosexuality are selected against.
Not every individual in a species has to be geared for reproduction, particularly if the species is very social and organizes itself into groups. In bees, for example, the vast majority of bees are totally infertile with just a handful of fertile bees in a single hive. It doesn't matter that the bees individually have terrible reproductive fitness, because the hive as a whole has very high reproductive fitness.
Monogamy isn't necessary; it works with polyandry and other arrangements such as levirate marriage too.
Are you explicitly suggesting group selection? It doesn't work outside of very special circumstances.
(The linked wiki article comes across as rather unpleasant in tone. Your user account is new and if you're new to the site, I don't want you to make you think this is typical. In that case please just use the wiki page as a link index to other articles about the subject, and for a counterpoint on when group selection might work after all, see e.g. this post.)
Eusocial insects make it work by making workers more related to their sisters than they would be to their own daughters. So workers prefer to raise their sisters than to give birth to their own sisters.
Bees are obviously a very extreme example of this but I think they're an apt one. The important point is that fertility is not selected for in bees, but instead, the activity of raising infertile workers.
The incorrect assumption about homosexuality is that a person is homosexual because of their genes. It's more likely that homosexuality is caused by the genes of the parent. After all while an individual is only concerned with his own reproductive fitness to the exclusion of his siblings, the parent is equally concerned with the reproductive fitness of all their children. It's true that homosexuality cannot be selected for, but a propensity to have homosexual children CAN be selected for if it increases the reproductive fitness of older siblings.
This is true, but it's not the same as in bees: there, it is in the interest of each worker not to have children and raise its sisters instead.
No, it isn't.
Workers do not have the ability to choose whether to be a queen or not. That choice is made for them when they are raised. A larva cannot feed itself royal jelly. And it should be obvious that given the choice, a worker would always choose to be a queen. After all, you're related to the existing queen (she's usually your mother or your sister), but you're even more related to yourself, so anything that increases your own reproduction at her expense is a good thing. Conversely, workers, given the choice, will almost always raise other bees as workers, because they are always more related to the existing queen than to her offspring.
No, from the point of view of their genes they are given a signal, they get to choose whether to obey it, i.e., a hypothetical mutation that causes the larva to develop into a queen even if not fed royal jelly doesn't seem like the kind of thing that would be hard to spontaneously happen.
Wikipedia says here that workers are 75% related to their sisters. They would only be 50% related to their own children after mating with an unrelated male. So mutations that cause larva to grow up as queens without royal jelly are actually deleterious. If workers were fertile, they would still evolve not to lay eggs while the queen is alive.