Man's brain just peachy

A diet high in fruit is known to keep people healthy, but it may also have helped us develop into humans, a new study suggests.

Scientists have discovered a link between the amount of fruit eaten by primates and the size of their brains.

Previously, it was thought that the larger brains of monkeys, apes and humans developed to cope with the complex social manoeuvrings required to live successfully in a group, a theory known as social brain hypothesis.

But researchers at New York University believe primates and humans ate their way to a bigger, more complex brain.

"Are humans and other primates big-brained because of social pressures and the need to think about and track our social relationships?" asked Dr James Higham, an assistant professor in NYU's anthropology department.

"Our findings do not support it. In fact, our research points to other factors, namely diet," he said.

The team compiled the biggest database of more than 140 different species to explore the relationship between brain size, different kinds of social behaviour and feeding habits.

Previous studies investigating brain-size evolution in primates found a correlation between the average number of group members and the size of their brain relative to body size. But the researchers found that the relationship vanished when more complex social behaviour - such as monogamy - was added into the mix.

They find no link between brain size and sociality, but they did find there was a strong link to diet.

Fruit-eating primates have about 25% more brain tissue than plant-eating species.

The American researchers suggest that the bigger brains probably evolved to recall fruit locations and work out new ways to extract flesh from tough skins.

Fruits also contain more energy than plants, giving brains a boost.

"Fruit is patchier in space and time in the environment and the consumption of it often involves extraction from difficult-to-reach-places or protective skins," said doctoral student Alex DeCasien, the lead author.

UK experts said the new study had turned evolutionary biology on its head.

Dr Chris Venditti, of the School of Biological Sciences at the University of Reading, said: "There is a long-standing notion that social complexity is linked to cognitive complexity.

"DeCasien et al may have delivered a blow to social brain hypothesis that has it reeling and if future work irons out some of the remaining methodological creases, it may be down and out.

"Then we will be left trying to explain primate cognition without sociality," he said.

The research was published in Nature Ecology and Evolution.

- ©The Daily Telegraph