Did Humans’ Big Brains Evolve To Make Us Better At Sizing Each Other Up?

Our social skills were a crucial part of early human development.

Did Humans’ Big Brains Evolve To Make Us Better At Sizing Each Other Up?
[Photo: Jesse Orrico via Unsplash]

Humans have very large brains compared to our body size. But how did we evolve brains this size?


You might expect it relates to our high levels of intelligence, capacity for abstract thinking and problem solving, or possibly to use tools. But really, according to a new study, our brain size is a “result of sizing each other up.”

Yup, our big brains, which are so important that we are born helpless and huge-headed, despite the dangers to our mothers as they struggle to birth us, evolved at least in part as organs for checking each other out.

The new study, from researchers at Cardiff University in the U.K., cites the social brain hypothesis, which posits that brain size is directly related to humans evolving in large and complex social groups.

[Photo: Flickr user Neil Conway]

The experiment used computer models to simulate a “donation game.” In the game, one simulated person would decide whether to not to make a donation to another simulated person. The decision was based on the reputation of the second person, and the reputations of both parties were updated after each round. What emerged, after running the simulation over and over, was that the simulated humans donated to those who were “at least as reputable” as themselves.

This, say the paper’s authors, represents “aspirational homophily,” or the desire to be like the other members of your group. Why does this make the brain bigger? Because it’s hard work making all those decisions:

We hypothesise that the cognitive challenge associated with social comparison has contributed to cerebral expansion and the disproportionate human brain size.

The paper goes on to detail the utility of social comparison and how discrimination and social norms can mold a society and help overall cooperation levels. But it’s a stretch to say that this is responsible for the growth of our brains.


On the other hand, other primates are often equally social and they also have pretty big brains. Also, our ability to function in a society and to cooperate is one of our defining qualities, as is our uncanny knack for reading people as soon as we meet them, so perhaps there is something to this after all.

Did the human brain, a multi-purpose tool that has proved so useful and flexible it allowed us to conquer our own planet (and subsequently begin to destroy it), evolve just to help us judge other people? Or is our ability to assess others a happy spinoff? You should, I guess, judge that one for yourself.

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About the author

Previously found writing at, Cult of Mac and Straight No filter.