Eating fruit and nuts helped humans develop bigger brains than other animals.
It had been thought that the social demands of living in groups fuelled the growth. But a study of more than 140 species of monkeys and apes claims it is actually down to the challenges of fruit gathering and the extra nutrition gained.
Figuring out how to harvest fruit, nuts and seeds may have helped train our minds. And fruit is more energy dense than leaves, aiding brain growth, according to the report in the journal Nature Ecology & Evolution. Fruit-eating primates have around 25 per cent more brain tissue than those that only eat leaves, the study found.
Author Alex DeCasien of New York University said there were many contradictions in the previous theories that attribute brain growth to social factors.