Primates, including humans, have larger brains than most other mammals, but why? Scientists searching for the answer have long followed a trail pointing to diet—specifically fruit—as the reason for why primates evolved larger brains. Primates, including humans, have larger brains than most other mammals, but why? Scientists searching for the answer have long followed a trail pointing to diet—specifically fruit—as the reason for why primates evolved larger brains. Plants & Animals Evolution Phys.org – latest science and technology news stories