From one piece David Reich – Bronze Age shock, the Neanderthal puzzle, & the sudden spread of farming 15 beliefs · youtube.com
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So we're talking about strong measurable selection coefficients on the order of half a percent or more in this study and all of those are going to work in small populations or large populations. It's not going to be affected by the population size.
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So for complex traits, ones underpinned by many mutations, all the variation already exists to move the population to a different adaptive set point that's optimal in the environment which it's in.
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But I think it's highly likely that if natural selection was pushed pushed any of these traits in more in one direction than it is, the mean would move.
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Your fat store from, you know, the latest hunt is not going to carry you through to the famine 3 years later. And so survival of famines is a different thing than building up body fat for being able to survive 2 weeks later.
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And so, maybe what you're seeing is that this group of people in Europe and the Middle East over the last 10,000 years has moved into a a period of relatively more stable food, where building up stores of fat are not as advantageous, and there's been selection against this combination of traits.
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my sense is that these complex traits have not pushed in one direction because there's advantage there's spectrums where there's advantages to both ends of the spectrum
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First of all, I think we are speaking from the point of view of a society which intensely values this particular trait, you know, ability to score well on IQ tests or things like them or to go to school for a long time or whatever it is. And I think this is unprecedented in human history that we live in a time like this.
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There seems to be some kind of general trait that maybe you could think of as executive function or maybe propensity to defer gratification or something or I'm just just waving my hands that is under selection and it pushes all these traits in the same direction one way or the other
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EuropeChinaeducationevolutionary biology
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So we just could not see a way this could happen by chance and once we saw that we really felt quite convinced that this was a real signal and that really somehow there has been natural selection to increase the genetic changes that today manifest themselves as more years of school at predicting more years of schooling.
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And what you see when you look at intelligence is you see that this maxes out in the Bronze Age between 5,000, 4,000, 3,000, 2,000 years ago. And the impact in the last 2,000 years is almost nothing. There's no evidence of natural selection at all.
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And really from a statistical point of view, what happens at these times of migration is there's just huge fluctuations in frequencies, and these are extremely uninformative times for looking and detecting natural selection.
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It may still be the case, and I guess it is, that immune traits are the most selected category, but is not at all the case, and in fact, we can prove it's not the case that behavioral traits are not selected.
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korrents.com
The Bronze Age, not the invention of farming, was the shock the human genome reacted to most strongly.Their words
our cartoon picture is that the big transition is farming, but the genetic data, the biological readout is saying our genome is reacting much more strongly to this these events that happened 5,000 years ago.
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Uh and 98% of it is other factors, especially genetic drift. So it's overwhelmingly migrations and population structure causing fluctuations in frequency.
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In fact, multiple analyses we do suggest that the genome is vibrating with natural selection, and uh there's all sorts of weaker effects that are there that would be picked up in larger studies even than we've done. Uh and that uh in fact, almost every position in the DNA is uh correlated to a position that in being dragged in one way or the other uh by natural selection. Instead of being quiescent, natural selection is everywhere.