Human evolution

Robin Dunbar

Why I looked at this book

Robin Dunbar is well known for the 'Dunbar number', that is the idea that the number of people fully in our social circle is limited to around 150 by the capacity of our brains and that this was a significant factor in the evolution of larger brains. I thought it would be interesting to see his thoughts on human evolution in more detail, which I am expecting this book to tell me. I'm also interested to see how his ideas fit in with other ideas of what was important in human evolution.

First impressions

Dunbar points out importance of sociality in human evolution, so that our development of music, say, should be up there with the development of tools. He also proposes a 'time budget' approach to the subject, investigating how each change in early human behaviour influenced the way they split up their time. The book dives straight into the topic in hand, where other books might begin more gently. This is fine, especially in a short book like this, but I'm slightly worried that while the introduction is accessible to a general readership, when the book gets on to more details it might be less so. I'll have to see.

Main review

I found that the book continued to be accessible to a general readership, but it is very much Dunbar putting forward his ideas rather than an overview of the wider field of human evolution. In fact I rather doubt that it deserves the word 'Introduction' in its title, it is more of a summary of the work done in the Lucy to Language: the Archaeology of the Social Brain project. (There are several other books with Lucy to Language in the title, so it couldn't be called that). I'd note that others in the 'Pelican Introduction' series also look to be more about a person putting forward an idea, rather than an introduction to a topic.

Dunbar clearly thinks social brain hypothesis can be taken as given, which I think is reasonable for the purpose of this book. He then looks at where this leads in terms of social behaviour as the size of the human brain increases, represented in terms of five transitions. A larger brain means a larger social group, which means that more time is required for social interactions. The main purpose of the book seems to be to explain where this extra time comes from, or how social interaction may take place in larger groups. Thus one-to-one grooming by chimpanzees gives way to singing, dancing and laughter in groups of humans. Cooking food enabled us to get more nutrition for a given investment in time. There's also a look at the origins of bipedalism and of pairbonding.

One problem I found with the book, particularly in terms of introducing people to evolutionary ideas, was that the benefits of a larger brain were not sufficiently explicit. To understand evolutionary arguments it is necessary to be clear about what the benefits of the changes are. In this book the social brain hypothesis means a larger group size, which means a higher cost in terms of the time spent socialising. This ends up making a larger brain look like a liability, whereas in reality it presumably has lots of benefits.

So I wouldn't recommend it if you are actually looking for an introduction to the topic, but well worth reading to find out about the social brain hypothesis and where it leads.