another view is that until the upper paleolithic, humans were frugivores (fruit eaters) who supplemented their meals with carrion, eggs, and small prey such as baby birds and mussels. only on rare occasions did they manage to kill and consume big game such as antelopes. this view is supported by studies of higher apes, particularly chimpanzees. chimpanzees are the closest to humans genetically. they share more than 96% of their dna code with humans, and their digestive tract is functionally very similar. chimpanzees are primarily frugivores, but they could and would consume and digest animal flesh, given the opportunity. in general, their actual diet in the wild is about 95% plant-based, with the remaining 5% filled with insects, eggs, and baby animals. in some ecosystems, however, chimpanzees are predatory, forming parties to hunt monkeys. some comparative studies of human and higher primate digestive tracts do suggest that humans have evolved to obtain greater amounts of calories from sources such as animal foods, allowing them to shrink the size of the gastrointestinal tract relative to body mass and to increase the brain mass instead.