Findings support view that big brains have evolved from diet rather than long-held theory it is due to social interaction
Foraging for fruit may have driven the evolution of large brains in primates, according to research attempting to unpick the mystery of our cerebral heftiness.
The finding appears to be a blow to a long-held theory that humans and other primates evolved big brains largely as a result of social pressures, with extra brain power needed to navigate and engage in complex social interactions. Instead the researchers say it supports the view that the evolution of larger brains is driven by diet.
All of these things are co-evolving: brains are getting bigger, sociality is becoming more complex, diet quality is becoming better, but it is maybe a shift in that focus on what might have been relatively more important, or more consistent throughout [primate] evolution, said Alex DeCasien, co-author of the research from New York University.
Writing in the journal Nature Ecology & Evolution, DeCasien and colleagues describe how they analysed the differences in brain size between more than 140 non-human primate species to unpick whether larger brains were linked to diet or to social factors. These factors included group size, mating habits and social system for example, whether a species was solitary or lived in a system where males are surrounded by a harem of females.
After taking into account factors such as body size and the position of species on the evolutionary tree, the team found no evidence that greater sociality is linked to bigger brain size.
Instead, they found that big brains appear to be linked to diet. According to the study, primates that eat fruit have about 25% more brain tissue than leaf-eaters of the same body weight. Omnivores were also found to have larger brains than leaf-eaters, although there was no difference when compared to fruit eaters.
DeCasien says the results support the idea that fruit-eating provides more energy than leaf-eating, aiding brain growth. [Fruit] is higher quality, it is more nutrient dense, it requires less digesting time, than the leaves, she said.