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Paris - Humans likely developed large and powerful brains, researchers said on Monday, with the help of what is today the simplest of snacks - fruit.
Eating fruit was a key step up from the most basic of foodstuffs, such as leaves, and provided the energy needed to grow bulkier brains, the scientists argued.
"That's how we got these crazy huge brains," said the study's corresponding author Alex Decasien, a researcher at New York University. "We have blown up the quality of our food that we are eating."
The study published in Nature Ecology & Evolution looked at the staple foods of over 140 species of primates, and assumed their diets haven't changed much over the course of recent evolution.
According to the research, the animals which feast on fruit have brains that are about 25% bigger than those filling their bellies primarily with leaves.
The results call into question the theory that has prevailed since the mid-1990s, which says bigger brains developed out of the need to survive and reproduce in complex social groups.
Decasien said the challenges of living in a group could be part of getting smarter, but found no link between the complexity of primates' social lives and the size of their grey matter.
What did correlate strongly with brain size was eating fruit.
Foods such as fruit contain more energy than basic sources like leaves, thus creating the additional fuel needed to evolve a bigger brain.
At the same time, remembering which plants produce fruit, where they are, and how to break them open could also help a primate grow a bigger brain.
A larger brain also needs more fuel to keep it running.
"We've heard that fact saying [our brain] is two percent of our body weight, but it takes up 25% of our energy," Decasien said.
"It's a crazy expensive organ."
While the study challenges some of the orthodoxy of how our brains evolved, the research is likely to continue.
"I feel confident that their study will refocus and reinvigorate research seeking to explain cognitive complexity in primates and other mammals," wrote Chris Venditti, a researcher at the University of Reading in Britain in a comment on the study, also published in Nature Ecology & Evolution.
"But many questions remain," he added.
