Fruit consumption has played a critical role in the evolution of human brains. According to a new study published Monday in the journal Nature Ecology & Evolution, we owe our large and powerful brains to fruits. Apes, monkeys, and humans have one of the highest brain-to-body size ratios. Researchers at the New York University found that primates that consumed higher amounts of fruits had significantly bigger brains than those that consumed only leaves or meat.

Fruits drove evolution of primates brains
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Fruit-eating primates had 25% bigger brains

Lead researcher Alex DeCasien argued that fruits provided the energy needed to grow bigger brains. DeCasien and her colleagues analyzed more than 140 primate species. They compared the primates’ brain sizes with the consumption of fruits, leaves, and meat. Researchers also took into account group size, mating systems, and social organization for the purpose of the study.

Scientists initially thought that they could determine whether social factors contributed to the evolution of brains by looking at various measures of sociality. But they couldn’t. They found that dietary preferences – mainly fruit consumption – played much bigger role in the growth of brain size. The study showed that primates filling their bellies primarily with fruits had 25% bigger brains than those feasting on leaves.

The frugivores or fruit-eating species also had significantly bigger brains than omnivores. DeCasien pointed out that our brain accounts for just 2% of our body weight, but it takes up nearly 25% of our energy. Fruits contain more energy than sources like leaves, thus providing additional fuel needed for the evolution of our brains. In turn, a larger brain is even more capable of scouring through the forests for more fruit.

DeCasien challenges the ‘social brain hypothesis’

Findings of the study call into question the long-held theory that our brains evolved due to the need to reproduce and survive in complex social groups. DeCasien’s study found no connection between the complexity of primates’ social lives and the size of their brains. According to Scientific American, the studies exploring “social brain hypothesis” in the past have yielded “inconsistent results.”

The new study uses a far more accurate evolutionary family tree, and had a sample size nearly three times larger than prior studies. DeCasien endorses the view that the complexity of fruit foraging might also have helped primate brain evolution. Searching for, picking and peeling a fruit requires more mental energy than just tearing off leaves. DeCasien said the foraging strategies, cognitive abilities, and social structures have “co-evolved throughout primate evolution.” But if the question is which factor is the most important, she says it’s fruit consumption.