It also shows that we are deluding ourselves if we think that we derive morality from holy books.
Big flaw: sociability is not morality. Cooperation is simply rational under many circumstances. That has been demonstrated by Axelrod and a whole legion of game-theorists after him.
Morality goes beyond mere cooperation: beyond reciprocity, etc. And it goes a long way beyond it. So where's the story how to get from sociability to morality via natural selection? Ther isn't one, just some handwaving.
Maybe morality like religion is just a mis-directed sequella of our tendency to trust authorities.
Anyways it's more than a bit of a leap to get from a monkey doing favors for another monkey who grooms him to something like the victorian masturbation taboo.
Cannibalism is worse than eating (other) meat, and that's true on a rational (not emotional) basis. Eating meat from another species is far less dangerous than eating meat from your own, because flesh of another species is less likely to contain parasites that can infect you. For animals that eat uncooked flesh (which was us humans until very recently) that's an overwhelmingly important consideration. And if you don't think so, look no further than kuru. Moreover as social animals, humans operated in groups -- and it is difficult to maintain group cohesion if everyone is sizing everyone else up as a potential meal. Behavior evolves, and is evolutionarily adaptive, so cannibalistic groups of humans would tend to be out-competed by groups which did not practice cannibalism. There's no need to invoke emotional, religious, or "ethical" reasoning.
Parasites have driven a lot of evolution -- in all species, not just humans -- and may even have been the reason sex evolved in the first place to increase genetic diversity. It's also very likely behind many of the other food taboos. In a society where germs and parasites are not understood, food hygiene practices are going to be pretty unnuanced, and they're going to be enforced by the only authority with any weight -- those who claim to speak on behalf of the reigning deity (or deities). Hence regions rife with trichinosis are going to consider pigs an unclean animal; most of the other kosher laws can be understood in the same way (the archaeological evidence suggests the non-semite neighbors of the israelite/judeans didn't raise pigs either). Likewise in an era without reliable birth control in a society where an unwed mother would be extremely burdened, a prohibition on premartial sex makes sense -- again enforced by the only authortities with any teeth: the priests.
Of course, modern food hygiene practices make kosher laws obsolete, just as reliable birth control makes injunctions against premarital sex obsolete, but unfortunately social evolution tends to lag technological evolution, particularly when there's no strong selective pressure to change. Mental dinosaurs linger well after the comet of progress should have snuffed them out.
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