In a world without cooking, we would have to spend half our days chewing raw food, much as the chimpanzee does. Cooking not only makes food more delicious, it also softens food and breaks starches and proteins into more digestible molecules, allowing us to enjoy our meals more readily and to draw more nutrition from them. According to Harvard University biological anthropologist Richard Wrangham, cooking’s biggest payoff is that it leaves us with more energy and time to devote to other things—such as fueling bigger brains, forming social relationships and creating divisions of labor. Ultimately, Wrangham believes, cooking made us human.

Archaeological evidence is mixed as to when our ancestors started building controlled fires—a prerequisite for cooking—but Wrangham argues that the biological evidence is indisputable: we must have first enjoyed the smell of a good roast 1.9 billion years ago. That is when a species of early human called Homo erectus appeared—and those hominids had 50 percent larger skulls and smaller pelvises and rib cages than their ancestors, suggesting bigger brains and smaller abdomens. They also had much smaller teeth. It makes sense that cooking “should have left a huge signal in the fossil record,” Wrangham says, and, quite simply, “there’s no other time that fits.” Never before and never again during the course of human evolution did our teeth, skull and pelvis change size so drastically. If cooking had arisen at a different point, he says, we would be left with a big mystery: “How come cooking was adopted and didn’t change us?”

Wrangham also has a theory as to how controlled fires, and thus cooking, came about. He speculates that H. erectus’s closest ancestors, the australopithecines, ate raw meat but hammered it to make it flatter and easier to chew, rather like steak carpaccio. “I’ve tried hammering meat with rocks, and what happens? You get sparks,” he says. “Time and time again this happens, and eventually you figure out how to control the fire.”