Language and conversation are distinctively human behaviours. But why should they
be unique to our species? The explanation lies in the phenomenon known as the
"social brain", a distinctively primate adaptation. Primates are characterised by two
unusual features: brains that are bigger for body size than is the case for any other
group of animals and some highly developed social skills. I shall show that these
features are correlated: primates' large brains have evolved because they are needed
to allow the animals to engage in more complex calculations when interacting
socially. This leads us to ask what it is that primates are doing that is so complicated
as to need a larger brain. The answer lies in aspects of social cognition like "theory of
mind" – the ability to understand how another individual sees the world. Pulling these
two themes together then allows us to see why and how language might have evolved
in the human lineage – and not anywhere else. Language is needed to supplement
social grooming (the main way in which primates bond their social groups) when
group size exceeds a certain limit. In effect, language is a form of grooming at a
distance that allows us to enlarge the circle of individuals that we can interact with.

Robin Dunbar graduated in Philosophy and Psychology from the University of
Oxford, and went on to do a PhD in animal behaviour at the University of Bristol.
During the last 30 years, he has studied the behaviour of wild primates and antelope in
various parts of Africa. More recently, his research has focussed on three main areas:
developing mathematical models of socio-ecological and reproductive decision-
making in primates, human behavioural ecology (with a particular emphasis on mate
choice strategies and parental investment decisions), and the cognitive mechanisms
that underpin these kinds of decisions in primates and humans. He leads a group of 3
faculty staff and around 15 postgraduate students working on a broad range of
subjects within these areas. His most recent books include: The Trouble with Science
(1995), Grooming, Gossip and the Evolution of Language (1996), The Evolution of
Culture (1999), Primate Conservation Biology (2000) and Human Evolutionary
Psychology (2002).