Large human brain evolved as a result of ‘sizing each other up’

Humans have evolved a disproportionately large brain as a result of sizing each other up in large cooperative social groups, researchers have proposed.

A team led by computer scientists at Cardiff University suggest that the challenge of judging a person’s relative standing and deciding whether or not to cooperate with them has promoted the rapid expansion of human brain size over the last 2 million years.

In a study published in Scientific Reports, the team, which also includes leading evolutionary psychologist Professor Robin Dunbar from the University of Oxford, specifically found that evolution favours those who prefer to help out others who are at least as successful as themselves.

Lead author of the study Professor Roger Whitaker, from Cardiff University’s School of Computer Science and Informatics, 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 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.”

In their study, the team used computer modelling to run hundreds of thousands of simulations, or ‘donation games’, to unravel the complexities of decision-making strategies for simplified humans and to establish why certain types of behaviour among individuals begins to strengthen over time.

In 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 they wanted to donate to the other player, based on how they judged their reputation. If the player chose to donate, they incurred a cost and the receiver was given a benefit. Each player’s reputation was then updated in light of their action, and another game was initiated.

Compared to other species, including our closest relatives, chimpanzees, the brain takes up much more body weight in human beings. Humans also have the largest cerebral cortex of all mammals, relative to the size of their brains. This area houses the cerebral hemispheres, which are responsible for higher functions like memory, communication and thinking.

The research team propose that making relative judgements through helping others has been influential for human survival, and that the complexity of constantly assessing individuals has been a sufficiently difficult task to promote the expansion of the brain over many generations of human reproduction.

Professor Robin Dunbar, who previously proposed the social brain hypothesis, 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.”

According to the team, the research could also have future implications in engineering, specifically where intelligent and autonomous machines need to decide how generous they should be towards each other during one-off interactions.

“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.”


  1. Blaise Frazier on

    It’s no wonder human society is so screwed up then. It’s obvious the vast, VAST majority of people use their brains for *nothing more* than sizing each other up and scrambling over and stepping on each other trying to climb the social ladder. People who actually put their brains to good use improving society are few and far in between, and often get shat upon by those who exist only to spend their whole existence living out horrific, glorified schoolyard political games.

    • James Ferlong on

      That’s because the biggest benefit or obstacle is always another human. You always have the most to gain by networking rapidly and you have the most to lose by destroying your reputation. Humans can dream of a world where they are not social creatures and you can often peacefully live that fantasy, but it is a fantasy.

      It’s just like all the zombie movies teach us. It’s not the zombie that you really have to to watch out for, it’s the desperate hungry things with fully functional brains and the will to do anything to live. They will also do a lot to compete and get easy money.

      Humans are dangers, they should handed with care.

      • Blaise Frazier on

        I just don’t view the world that way, and it’s a shame other people do. If they spent more time focusing on how cooperate and behave compassionately with a focus on the greater good, instead of their own inflated sense of greed and selfishness, the world would be a better place.

        • Dis Concussion on

          I suppose as an adult that’s fine, but socialization is essential to our development. Look to the kids who were raised by animals to understand that – they end up permanently severely mentally retarded.

          You’re only looking at the negative aspects of interacting with people. You can still have a close-knit group of friends that you deem to be good people. They are out there and worth having in your life. Sure, it’s a risk to get attached to anyone emotionally, but it’s a risk/reward balance. If you choose to neglect your social life in favor of living life your way then so be it. I just hope you feel like you’re doing something meaningful.

  2. Strange how the smartest of us are the ones that are the ones that are least socially capable.

    • Dis Concussion on

      That’s not necessarily true. Some prominent thinkers are certainly socially underdeveloped, probably disproportionately so, but plenty are well adjusted citizens as socially capable as anyone else.

  3. James Ferlong on

    That’s how much brain power we have to waste trying to figure each other out and the smarter we get the smarter we have to be to figure each other out. There is nothing in the universe more complex than human behavior.

    At first you might think NAH, humans are finite creatures of X molecules, but that whole free will thing and ability to cooperative deny reality. It means we can choose complex behaviors that don’t fit the pattern of any other object or combination of particles.

    Nothing in the universe behaves as randomly as humans can and to attempt to figure that out, particularly as time goes on a models only get more complex. It’s the never ending problem that science always dreamed of and it’s always right here in front of you, not billions of light years through space. Consider that Einstein was primarily a thought experiment guy, the human ability to approximate and guess as well as it can is not understood. That’s just ONE human brain. Now imagine all the other geniuses of the world who are trapped in poverty or just left unnoticed.

    Humanity has more brain power than it has governing ability. Partly due to our naturally competitive nature, which if course ensures we keep getting smarter as well, if only to beat each other at everything.

  4. Raymond Supan on

    To me this explains why there is racism, xenophobia, “judging a book by its cover”, social-class, religious and cultural bias, rival gangs, rival sports team fans a little bit to me. It seems humans have an ingrained judgmental aspect that came with the evolution of larger brain size and cooperation.

  5. your opinion doesn't matter on

    Well thank god you agree. I thought it was questionable when it was just computer scientists and Cardiff but now that I know Shmee is on board I have no doubts.

  6. What a load of bullshit, humans never evolved and cant evolve, stupid pseudoscientists better play with their lab rats.