The social intelligence hypothesis

ABC Radio’s Science Show just had a special edition on the evolution of the brain and the development of social intelligence.

The programme talks to some of the leading researchers in social intelligence whose research interests range from comparing the behaviours of animals across species, to neuroimaging humans, to building robots to mimic social interaction.

In particular, the programme tackles the ‘social intelligence hypothesis’ that suggests that our increase in brain size during evolution has been driven by the need to work in groups and make sense of complex relationships.

Prof Steven Mithen explains:

There seems to be two key figures of brain expansion, and I think this is where the social intelligence hypothesis becomes very interesting. The first was around two million years ago, and at that time brains expanded perhaps about 50%. So we went from brain size of around 450cc to a brain size of around 1,000cc by 1.8 million years ago. What’s interesting during that time is that we don’t see dramatic changes in human behaviour as represented by the archaeological remains….

So archaeologists asked; why are brains getting larger and what is it providing? Brains wouldn’t get larger just for any reasons because brain tissue is metabolically very expensive, so it’s got to be serving a really important purpose. I think the social intelligence hypothesis suggests to us that that expansion of brain size around two million years ago was because people were living in larger groups, more complex groups, having to keep track of different people, a larger number of social relationships which we simply required a larger brain to do.

Link to Science Show special on ‘The social intelligence hypothesis’.

4 thoughts on “The social intelligence hypothesis”

  1. Put under Darwinian eyes, this somehow does sound odd. If there ever were a link between the size of the brain and our social behaviours, it would be the other way around : we would become more social because our brain allows it, not grow our brain because the environment requires it.
    We all know our ancesters standing straight allowed the brain to have more space to expand. Some developed bigger brain, which, hypothetically, would allow these individuals to keep better track of social activities, thus giving them advantages over smaller brains, thus smaller brains disappearing eventually, and our species becoming big brains species.
    this just does not sound realistic to me.
    It’s a bit like saying our brain will get bigger because we have the internet and so many blogs to keep track of. Sounds really more funny than serious to me 🙂

  2. Well the correlation of brain size and social size has been made in Primates. A Zoologist can estimate social size based on brain size. It’s that simple really. The larger the social group, the larger the brain.
    Humans have been the largest social group, thus the largest brain. Interesting yet, humans have a very vast social group in the sense that our history and culture are so preserved [writing, video, religion, culture] so in some sense our social group consist of people who are now dead. This gives you an idea of how massive our social group is.
    Now your internet example may get our brains to bigger, IF there is a selective force involved, but there isn’t. People will continue to reproduce regardless of wither or not they can retain blog information. However, in a more primitive environment, having a smaller brain would put your genes at risk.

  3. In response to Pixeline and his/her first paragraph in the post above, i think that the answer is in the proocess and concept of “Niche Construction” how the coupled interactions between organisms and enviroment mutually affect both, the organism and the enviroment, redirecting them to new selection pressures. In its nuts and bolts the “social intelligence hypothesis” is a very good heuristics.

  4. From what I understand, the lifestyle of the Orangutans disprove this theory. They have large brains relative to their body size, yet they live mostly solitary lives.

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