Scientists May Have Finally Answered Why We Have Such Big Brains

A team of researchers from Cardiff University believe they have finally answered a question that has plagued scientists for years: Why do humans have such disproportionately large brains?

Published in the journal Scientific Reports, the newly released study suggests that the incredible development of the brain is connected to the formation of large, cooperative social groups.

As humans started having to judge a person’s relative standing and making decisions about who to cooperate with, their brains’ were challenged like never before. The team of computer scientists from Cambridge believe it was this which promoted the rapid expansion of brain size over the last two million years.

The authors also claim that their results show that evolution favours those who are willing to help and cooperate with others who are at least as successful as themselves.

“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 up and making decisions as to whether we want to help them or not.” explained lead author Roger Whitaker, from Cardiff University’s School of Computer Science and Informatics.

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

In comparison to almost every other animal, human brains are larger as a percentage of body weight. More remarkably, since the emergence of the first species of the Homo genus some two million years ago, the human brain has more than doubled in size. Compared to more distant ancestors such as the australopithecines, which lived between two and four million year ago, human brains have more than tripled in size.

What accounted for this remarkable increase has long puzzled scientists.

The Cardiff University team used computer modelling to run hundreds of thousands of simulations, or ‘donation games’, as a means to understand decision making strategies in simplified humans. From these simulations they attempted to understand why certain types of behaviour strengthened over time.

For each round of the donation game, two simulated players were randomly selected from the population. The first player then made a decision on whether or not to donate to the second, based on a judgement of the second player’s reputation. If the player elected to donate, the first suffered a cost while the second received a benefit. Their reputation was then updated in light of their decision, before the next game was initiated.

According to the team, the results suggest making relative judgments to help others has been important for human survival. They also claim that the complexity involved in having to regularly assess and reassess individuals has been difficult enough to promote the expansion of the human brain through the generations.

Professor Robin Dunbar, an evolutionary psychologist from Oxford University who was involved in the study, previously proposed the social brain hypothesis. “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.” he explained.

“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.”

The implications of the study are not just limited to understanding our most ancient history, however. The authors suggest it could also be applied to engineering and in particular to the development of autonomous machines.

“The models we use can be executed as short algorithms called heuristics, allowing devices to make quick decisions about their cooperative behaviour,” Professor Whitaker said.

“New autonomous technologies, such as distributed wireless networks or driverless cars, will need to self-manage their behaviour but at the same time cooperate with others in their environment.”

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