Hamilton's doctoral thesis, at Imperial College, London, was a mathematical study of why some insects such as ants and bees live in colonies and help each other. Unlike all his rivals, he came not to praise altruism, but to bury it, for his theory was that close co-operation between relatives is not altruism at all but a self-interested attempt to preserve copies of genes that relatives share. This 'kin-selection' theory is now the uncontroversial foundation of much evolutionary thought.
Disappointed by the lack of support for his ideas in Britain, Hamilton went to the University of Michigan. Combining an encylopaedic knowledge of insect habits with good mathematical intuition, he was soon making his mark all over the field of evolution. In 1967 he wrote a prescient paper predicting the discovery of internecine warfare among genes within cells over access to the next generation: 'intragenomic conflict' is now one of the fastest-growing and most exciting fields in biology.
By the 1980s, now at Oxford, he turned his attention to the problem of sex. His main contribution was to build a computer model of the genetic battle between parasites and hosts. When Hamilton runs the simulations, his computer screen fills with a red transparent cube inside which two lines, one green and one blue, chase each other like fireworks on a slow-exposure photograph, as the parasite pursues the host through genetic 'space'. Under realistic conditions, a sexual host can forever keep one step ahead of a parasite. But only if it never stops changing.