Humans have big brains, and those brains come with a big appetite for energy. Nutritional scientists from the University of Sydney and University of Glasgow modeled dietary intake versus energy needs for varying brain and body sizes across 4 million years of hominin evolution. According to the team, natural sugars from fruit, honey, and other sweet foods provided roughly 20 to 35 percent of energy intake throughout hominin evolution. After our ancestors tamed fire, they were able to unlock the complex carbohydrates in starchy foods, like tubers. “The evidence suggests that carbohydrate-rich foods helped fuel the energy demands of our growing brains,” Brand-Miller said.