A high-fruit diet 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 maneuverings required to successfully live in a group, a theory known as social brain hypothesis.

For example primates need substantial brainpower to understand who their friends and enemies are, and keep track of ever-changing hierarchies and power struggles.

But researchers at New York University believe primates and humans actually 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, as some have argued?" said Dr James Higham, an assistant professor in NYU's Department of Anthropology.

"This has come to be the prevailing view, but our findings do not support it. In fact, our research points to other factors, namely diet."