The tale of how humans became such avid carnivores begins 65 million years ago. The dinosaurs have just gone extinct, together with over half of Earth’s species. In rainforests that carpet vast areas of the planet, among soaring trees ribboned with vines, our next ancestor has just evolved. It’s the first primate ever known: Purgatorius. It doesn’t look much like you or me, or even like a chimp. It resembles a cross between a mouse and a squirrel. And if it were still alive today, it would likely pass for a cute pet.
Purgatorius was an accomplished tree climber—and a vegan. It gave up the insect-based diet of its ancestors in favor of newly abundant fruits and flowers, carving for itself a comfortable niche high in the branches. For tens of millions of years, the descendants of Purgatorius were committed to their plant-based diets. From small monkeys to gorilla-size apes, they survived mostly on tropical fruits, spicing their meals with occasional worms (often by accident). Around 15 million years ago, they diversified a bit, adding hard seeds and nuts to their diets, but stayed true to their vegan roots.
Then, around 6 million years ago, Sahelanthropus tchadensis entered the African primate scene. With the advent of Sahelanthropus, our lineage likely split from that of our closest cousins, the chimps and bonobos. In the language of paleoanthropology, the word hominin stands for modern humans and all the extinct species closely related to us—and Sahelanthropus was the first. A short, flat-faced, small-brained creature, it most likely walked upright on two legs. It had smaller canine teeth than its ancestors and thicker tooth enamel, which suggests that its diet required more chewing and grinding than Purgatorius-like meals of fruits and flowers.