This is Ridley's second book on evolution (his first was "The Red Queen" and dealt with the reason for the existence of sex). He belongs firmly in the school of thought that looks for a biological basis for human behaviour. In this book he considers how our social order has arisen on a basis of self-interest. Selfishness, he argues, is built into our biology at the most basic level, that of the gene, and the same principle applies to the development of the organism as a unit. But it doesn't stop there; it exists in societies too. Here Ridley draws heavily on the Prisoner's Dilemma and its offshoots. Apparently altruistic behaviour, he argues, is really rational, based on intuitive but accurate calculations of profit and loss in different situations.
Turning to the roots of war, he sees this as arising from group selection. Groups in competition with one another inevitably find themselves in conflict. He draws some of his examples from near home, including rivalry between users of Apple-Macintosh and IBM PC computers; I can see the same thing at work nearer at hand between enthusiasts for Linux and Windows(TM). Being a member of a group provides security for individuals. This is of course potentially dangerous; being a member of a group can lead one to participate in dubious enterprises, as in Nazi Germany or Maoist China.
As Ridley himself acknowledges, there is nothing original in any of this; he is popularizing ideas which are already current among many biologists and anthropologists, but he does it well. He could perhaps be accused of over-simplifying the complexity of human society, and, as a journalist as well as a science writer, he has a political message: he wants the power of the state to be reduced to give more autonomy to smaller groups; he believes that small is beautiful and that the pursuit of self-interest will lead to a more equitable world. This is an attractive idea but I did wonder if it was a little romantic and over-optimistic. Nevertheless, the general argument of the book seems to be convincing.