It was about 2.6 million years ago that meat first became a significant part of the pre-human diet, and if Australopithecus had had a forehead to slap it would surely have done so. Being an herbivore was easy—fruits and vegetables don’t run away, after all. But they’re also not terribly calorie-dense. A better alternative were so-called underground storage organs (USOs)—root foods like beets and yams and potatoes. They pack a bigger nutritional wallop, but they’re not terribly tasty—at least not raw—and they’re very hard to chew. According to Harvard University evolutionary biologists Katherine Zink and Daniel Lieberman, the authors of the Nature paper, proto-humans eating enough root food to stay alive would have had to go through up to 15 million “chewing cycles” a year.
This is where meat stepped—and ran and scurried—in to save the day. Prey that has been killed and then prepared either by slicing, pounding or flaking provides a much more calorie-rich meal with much less chewing than root foods do, boosting nutrient levels overall. (Cooking, which would have made things easier still, did not come into vogue until 500,000 years ago.)
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