An apple a day can keep the doctor away, but that's nothing compared to what it can do for primates, at least according to a study published Monday in Nature Ecology & Evolution. Scientists have long hypothesized that primates evolved large brains because they needed them for complex social interactions, the Guardian reports. But researchers behind the new study say big brains may have actually evolved because of eating fruit. Researchers looked at 140 primate species and found no evidence of a link between brain size and complexity of social behavior. They did, however, find a link between diet and brain size. Specifically, primates that ate fruit had about 25% more brain tissue than primates of a similar size that ate leaves.
The idea is that fruit contains more nutrients and provides more energy than leaves, helping brains to grow. However, it could also be that it takes a lot more mental power to eat fruit (finding it, determining ripeness, opening it, etc.) than simply picking some leaves off a nearby tree. NPR reports this might be why spider monkeys have bigger brains than howler monkeys, which are similar in size and live in similar social groups in the same area: While howler monkeys are sitting around eating leaves, spider monkeys are foraging for fruit. Other researchers aren't so sure. One expert points out that while fruit may provide more energy for growing brains, something else is needed to explain why that energy is used for brain growth, according to Science Magazine. (Fruit giveth, and fruit taketh away: Deadly brain illness blamed on fruit.)