Fruit is full of sugar, and our brain relies on glucose, a sugar, as its primary energy source. Now, in a new analysis published in Science on Thursday, Brand-Miller and her colleagues argue that sugar played a “central” part in human evolution, particularly early on. Over the span of human evolution, hominins accumulated 20 to 35 percent of their energy from these foods, the analysis found. In fact, there is fossil evidence to suggest Lucy’s diet could have been more like that of primates “that eat very different foods,” he says. Ultimately, the takeaway fits with what most researchers think early humans ate—which what popular ideas about meat-rich Paleo diets might suggest.