My tummy is more tender than it used to be. Not more tender than 10 years ago, but more tender than 2½ million years ago. The human digestive tract is the product of more than 5 million years of evolutionary change. In that span, human diets have changed greatly. In Africa 2.5 million years ago, human ancestors were foragers and scavengers. Human exposure to unfriendly microbes and parasites …
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