Marta Zaraska writes: Just as modern chimps occasionally hunt colobus monkeys, our ancestors may have occasionally dined on the raw meat of small monkeys, too. Yet the guts of early hominins wouldn’t have allowed them to have a meat-heavy diet, like the one Americans eat today. Their guts were characteristic of fruit-and-leaf eaters, with a big caecum, a bacteria-brimming pouch at the beginning of the large intestine. If an australopith gorged himself on meat — say, ate a few zebra steaks tartare in one sitting — he likely would have suffered twisting of the colon, with piercing stomach pains, nausea, and bloating, possibly resulting in death. And yet in spite of these dangers, by 2.5 million years ago, our ancestors had become meat eaters.

It seems that our bodies had to adjust gradually, first getting hooked on seeds and nuts, which are rich in fats but poor in fiber. If our ancestors ate a lot of them, such a diet would have encouraged the growth of the small intestine (where the digestion of lipids takes place) and the shrinking of the caecum (where fibers are digested). This would have made our guts better for processing meat. A seed-and-nut diet could have prepared our ancestors for a carnivorous lifestyle in another way, too: It could have given them the tools for carving carcasses. Some researchers suggest that the simple stone tools used for pounding seeds and nuts could have easily been reassigned to cracking animal bones and cutting off chunks of flesh. And so, by 2.5 million years ago, our ancestors were ready for meat: They had the tools to get it and the bodies to digest it.

But being capable is one thing; having the will and skill to go out and get meat is quite another. So what inspired our ancestors to look at antelopes and hippos as potential dinners? The answer, or at least a part of it, may lie in a change of climate approximately 2.5 million years ago. [Continue reading…]