William Donald Hamilton (1 August 1936 – 7 March 2000) was a British evolutionary biologist, recognised as one of the most significant evolutionary theorists of the 20th century.
Hamilton became known for his theoretical work expounding a rigorous genetic basis for the existence of altruism, an insight that was a key part of the development of the gene-centered view of evolution. He is considered one of the forerunners of sociobiology. Hamilton published important work on sex ratios and the evolution of sex. From 1984 to his death in 2000, he was a Royal Society Research Professor at Oxford University.
Richard Dawkins has written that Hamilton was "the greatest Darwinian of my lifetime".
Early life
Hamilton was born in 1936 in Cairo, Egypt, the second of seven children. His parents were from New Zealand; his father A.M. Hamilton was an engineer, and his mother B.M. Hamilton was a physician. The Hamilton family settled in Kent. During the Second World War, Hamilton was evacuated to Edinburgh. He became interested in natural history at an early age and spent his spare time collecting butterflies and other insects. In 1946, he discovered E.B. Ford's New Naturalist book Butterflies, which introduced him to the principles of evolution by natural selection, genetics, and population genetics.
He was educated at Tonbridge School, where he was in Smythe House. As a 12-year-old, he was seriously injured while playing with explosives his father had that were left over from making hand grenades for the Home Guard during World War II. Hamilton had to have a thoracotomy and parts of fingers on his right hand had to be amputated in King's College Hospital to save his life. He was left with scarring and needed six months to recover.
Before going up to the University of Cambridge, he travelled in France and completed two years of national service. As an undergraduate at St. John's College in Biology, he was uninspired by the "many biologists [who] hardly seemed to believe in evolution".
Hamilton's rule
Hamilton enrolled in an MSc course in demography at the London School of Economics (LSE), under Norman Carrier, who helped secure grants for his studies. Later, when his work became more mathematical and genetical, he had his supervision transferred to John Hajnal of the LSE and Cedric Smith of University College London (UCL).
Both Fisher and J. B. S. Haldane had seen a problem in how organisms could increase the fitness of their own genes by aiding their close relatives, but not recognised its significance or properly formulated it. Hamilton worked through several examples, and eventually realised that the number that kept falling out of his calculations was Sewall Wright's coefficient of relationship. This became Hamilton's rule: in each behaviour-evoking situation, the individual assesses his neighbour's fitness against his own according to the coefficients of relationship appropriate to the situation. Algebraically, the rule posits that a costly action should be performed if:
where C is the cost in fitness to the actor, r the genetic relatedness between the actor and the recipient, and B is the fitness benefit to the recipient. Fitness costs and benefits are measured in fecundity. r is a number between 0 and 1. His two 1964 papers entitled The Genetical Evolution of Social Behaviour are now widely referenced.
The proof and discussion of its consequences, however, involved detailed mathematics, and two reviewers passed over the paper. The third, John Maynard Smith, did not completely understand it either, but recognised its significance. Having his work passed over later led to friction between Hamilton and Maynard Smith, as Hamilton thought Maynard Smith had held his work back to claim credit for the idea (during the review period Maynard Smith published a paper that referred briefly to similar ideas). The Hamilton paper was printed in the Journal of Theoretical Biology and, when first published, was largely ignored. Recognition of its significance gradually increased to the point that it is now routinely cited in biology books.
Much of the discussion relates to the evolution of eusociality in insects of the order Hymenoptera (ants, bees and wasps) based on their unusual haplodiploid sex-determination system. This system means that females are more closely related to their sisters than to their own (potential) offspring. Thus, Hamilton reasoned, a "costly action" would be better spent in helping to raise their sisters, rather than reproducing themselves.