This is why genetic evolution kicked into overdrive in the Holocene era, pulling along mutations such as the lactose tolerance gene, or a gene that changed the blood of Tibetans so that they could live at high altitudes.83 Genes for these recent traits and dozens of others have already been identified.84 If genetic evolution was able to fine-tune our bones, teeth, skin, and metabolism in just a few thousand years as our diets and climates changed, how could genetic evolution not have tinkered with our brains and behaviors as our social environments underwent the most radical transformation in
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