The exodus from africa happened at least 40,000 years ago though. That's long enough for as trivial a change as melatonin variation to stabilize. "Civilization" has only been going on for the past 10,000 years that we know of. And that's with a very small percentage of the human population. I would expect that any selective pressure against the hypothesised ability has only arisen over the course of the past 500 years [i]averaged out[i] over the species. That's about 25 generations. And it's a very very light selective pressure at that. |
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