Is there a 'physics of society'? Philip Ball's investigation into human nature ranges from Hobbes and Adam Smith to modern work on traffic flow and market trading, across economics, sociology and psychology. Ball shows how much of human behaviour we can understand when we cease trying to predict and analyse the behaviour of individuals and look to the impact of hundreds, thousands or millions of individual human decisions, in circumstances in which human beings both co-operate and conflict, when their aggregate behaviour is constructive and when it is destructive. By perhaps Britain's leading young science writer, this is a deeply thought-provoking book, causing us to examine our own behaviour, whether in buying the new Harry Potter book, voting for a particular party or responding to the lures of advertisers.