My, what a beautiful mind you have: Sizing up other people helped humans evolve their big brains

A bit of healthy competition is often regarded as a good way of helping people improve their performance.

But it seems we may owe our big brains to our tendency to size each other up too.

A team of scientists have found that judging other people's standing in a group appears to have played a key role in the evolution of human brain size over the past two million years.

They found that evolution appears to favour those who choose to cooperate with people who are at least as successful as themselves.

Making these judgement, however, is a complex task and may have driven the expansion of the higher functions of our brains.

Professor Roger Whitaker, a computer scientist at Cardiff University who led the research, said: 'Our results suggest that the evolution of cooperation, which is key to a prosperous society, is intrinsically linked to the idea of social comparison – constantly sizing each other up and making decisions as to whether we want to help them or not.

'We've shown that over time, evolution favours strategies to help those who are at least as successful as themselves.'

The study, which is published in the journal Scientific Reports, used computer modelling to simulate the way humans make decisions about others.

They did this by creating games that required computerised players to make decisions about whether to donate items to others.

Professor Robin Dunbar, an evolutionary psychologist at the University of Oxford who was a co-author of the study, said the findings reinforce the idea that human brains grew as our species adapted to cooperate with each other.

So while we now make judgments about others in a fraction of a second now, our early ancestors may have found the task far more taxing. 

Humans have the largest cerebral cortex of all mammals relative to the size of their brains – an area which is responsible for higher functions like memory, communication and lateral thinking.

The researchers say that making judgments about whether to cooperate with others requires these abilities and so drove the growth of the brain.

Professor Dunbar said: 'According to the social brain hypothesis, the disproportionately large brain size in humans exists as a consequence of humans evolving in large and complex social groups.

'Our new research reinforces this hypothesis and offers an insight into the way cooperation and reward may have been instrumental in driving brain evolution, suggesting that the challenge of assessing others could have contributed to the large brain size in humans.'