In Memory of Bill Hamilton

William Donald Hamilton, Darwins heir, died on March 7th, aged 63

by Olivia Judson (The Economist)

All his life, Bill Hamilton played with dynamite. As a boy, he nearly died when a bomb he was building exploded too soon, removing the tips of several fingers and lodging shrapnel in his lung. As an adult, his dynamite was more judiciously placed. He blew up established notions, and erected in their stead an edifice of ideas stranger, more original and more profound than that of any other biologist since Darwin. Like Darwin, he was a naturalist first, attending, as he put it, the funeral feasts of dead trees: greedily stripping bark from rotting branches to marvel at the immense diversity of creatures devouring the wood below. Later, he worked in Brazil, in the jungles of the interior, and in the flooded forests­that part of the Amazon basin where, for half the year, fish eat fruit and canoeists paddle about among the treetops. He recounted tales of sleeping in a hammock under the stars and waking to find that termites had eaten his socks; he claimed to have been stung by more than 1,000 species of wasp.

Perhaps it was all this that gave him the knack of seeing the world from another point of view. Whatever he looked at­be it a fly spinning silk balloons in the hopes of winning a mate, an oak tree wanting to get its acorns planted, or a nameless parasite plotting to hijack a host­he could put himself there, and imagine what he might do in such circumstances. As a writer of natural history, he was superb. But often, he went further, imagining himself as a gene within an organism: in his theoretical work (published under his initials, though everyone knew him as Bill), he explored how genes could spread even if they were bad for the creatures they belonged to. He showed how natural selection could act not just on the individual, as Darwin had thought, but on individual genes. Like Darwin, what he found has powerful­and to some, disturbing­implications for humans and human behaviour.

The trouble with altruism

At Cambridge University, Bill Hamilton studied genetics. Then, at the London School of Economics, he spent three years working out the genetics of altruistic behaviour. He released a genie: in three terse papers, he founded the discipline known as sociobiology.

From an evolutionary standpoint, the trouble with altruism is that if an altruistic behaviour is costly­for example, dying for someone else­then the genes that promote it should quickly disappear from the population. Yet examples of self-sacrifice abound in animal societies. The most conspicuously selfless are the social insects, the ants, bees and wasps in which most individuals work tirelessly for the good of the colony and never reproduce themselves. Professor Hamilton argued that such extreme altruism is most likely to evolve if, by sacrificing themselves, individuals increase their "inclusive fitness"­that is, the proportion of their genes carried by others in the population. "Hamilton´┐Żs rule" is the mathematical formulation of this; put crudely, it amounts to the idea that you can die for close kin and still spread your genes, since close kin have many genes in common with you.

For Professor Hamilton, this was just one facet of the more general problem of how natural selection works. Inclusive fitness showed how traits bad for individuals could sometimes persist for the good of a group; but what about the converse? Could a gene spread even if the only beneficiary were the gene itself? He found it could, thus pioneering the now familiar notion of a "selfish gene" along with its curious corollary­that genes within an organism are often in conflict with one another.

He became fascinated by sex ratios: why did so many insects produce sex ratios that were wildly skewed, sometimes 50 females to every male? His answers ultimately brought him to the problem: why does sex exist at all? He thought it impossible to overstate the role of harmful parasites as agents of natural selection, and that only by shuffling genes between generations (ie, having sex) could populations hope to escape annihilation.

He was both horrified and gratified by what his genie wrought. Gratified, because the idea of inclusive fitness has enormous explanatory power, even for human behaviour. Horrified, because of its implications for human nature­which still make sociobiology a controversial discipline. He derided politically correct claims that humans alone are magically free of genetic influences in their behaviour. However, he was quick to stress that while a study of evolution may tell us how we came to be, it says nothing about what we should strive to become.

He was recognised late. He seemed bemused by his transformation from loner to the man everyone wanted to speak to, and perhaps as a defence, he was absent-minded: he had only one lecture a year to give at Oxford, but sometimes he forgot to turn up.

In recent years, he became interested in the origins of HIV, the virus that causes AIDS. Seeing that the question could only be resolved with viral samples from wild chimpanzees, he went off to get some. On the second of two trips to Congo, he fell sick with a tropical disease and died. He was carrying out an act of altruism, and it was a parasite that got him.