ALTRUISM – helping others at a cost to oneself – has been a stubborn thorn in the side of evolutionary biologists. If natural selection favours genes that produce traits which increase the reproductive success of the individuals in which they reside, then altruism is precisely the sort of behaviour that should disappear.
Darwin was acutely aware of the problem that altruism posed for his theory of natural selection. He was particularly worried about the self-sacrificial behaviour that social insects display: how could natural selection explain why a worker bee will defend its hive by stinging an intruder and dying in the process? In On the Origin of Species, he summarised the topic of social insect altruism as “one special difficulty, which at first appeared to me to be insuperable, and actually fatal to the whole theory”. But then he came up with an explanation.
Since worker bees were helping blood relatives – especially their queen – Darwin hypothesised that natural selection might favour altruism at the level of blood kin. One hundred and four years later, the biologist Bill Hamilton would formalise Darwin’s idea, but the path from Darwin to Hamilton was not smooth. The nature of altruism and its similarities to the human trait of goodness make it susceptible to political, philosophical and religious subjectivity. Studying the structure of an atom isn’t personal: studying altruism can be. It certainly was for the next two figures in the history of altruism, Thomas Huxley and Peter Kropotkin.
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Huxley, also known as “Darwin’s bulldog”, outlined his thoughts on this topic in an 1888 essay entitled “The struggle for existence”: “From the point of view of the moralist, the animal world is on about the same level as the gladiator’s show… Life [for prehistoric people] was a continuous free fight, and beyond the limited and temporary relations of the family, the Hobbesian war of each against all was the normal state of existence.” For Huxley, altruism was rare, but when it occurred, it should be between blood relatives.
Kropotkin, once a page to the tsar of Russia and later a naturalist who spent five years studying natural history in Siberia, thought otherwise. In Siberia he thought that he saw altruism divorced from kinship in every species he came across. “Don’t compete!” Kropotkin wrote in his influential book Mutual Aid: A factor of evolution (1902). “That is the watchword which comes to us from the bush, the forest, the river, the ocean. Therefore combine – practice mutual aid!”
How could two respected scientists come to such radically different conclusions? In addition to being a naturalist, Kropotkin was also the world’s most famous anarchist. He believed that if animals could partake in altruism in the absence of government, then civilised society needed no government either, and could live in peace, behaving altruistically. Kropotkin was following what he saw as “the course traced by the modern philosophy of evolution… society as an aggregation of organisms trying to find out the best ways of combining the wants of the individuals with those of co-operation”. He saw anarchism as the next phase of evolution.
Huxley was no less affected by events around him. Shortly before he published “The struggle for existence”, his daughter, Mady, died of complications related to a mental illness. In his despair over Mady’s passing he wrote, “You see a meadow rich in flower… and your memory rests upon it as an image of peaceful beauty. It is a delusion… not a bird twitters but is either slayer or slain… murder and sudden death are the order of the day.” It was in the light of nature as the embodiment of struggle and destruction – the antithesis of altruism – that Huxley saw the death of his daughter and it was in that mindset that he penned his essay.
A suite of other fascinating characters would follow Huxley and Kropotkin. In the US there was the Quaker ecologist Warder Clyde Allee, who did the first real experiments on altruism in the 1930s and whose religious and scientific writings on the subject were often indistinguishable; in fact, he would often swipe text from one and add it to the other. Around the same time in the UK, J.B.S. Haldane, one of the founders of population genetics, was talking of altruism and kinship, and came close to developing a mathematical theory on the subject. But he stopped short – nobody quite knows why.
A mathematical theory for the evolution of altruism and its relation to blood kinship would come a generation later with Bill Hamilton, who was both a passionate naturalist and a gifted mathematician. While working on his PhD in the early 1960s, he built a complex mathematical model to describe blood kinship and the evolution of altruism. Fortunately, the model boiled down to a simple equation, now known as Hamilton’s rule. The equation has only three variables: the cost of altruism to the altruist (c), the benefit that a recipient of altruism receives (b) and their genetic relatedness (r). Hamilton’s rule states that natural selection favours altruism when r × b > c.
Hamilton’s equation amounts to this: if a gene for altruism is to evolve, then the cost of altruism must be balanced by compensating benefits. In his model, the benefits can be accrued by blood relatives of the altruist because there’s a chance (the probability r) that such relatives may also carry that gene for altruism. In other words, a gene for altruism can spread if it helps copies of itself residing in blood kin.
A generation of biologists were profoundly affected by Hamilton’s rule. One them was the population geneticist George Price, an eclectic genius who became depressed when he came across Hamilton’s work. He had hoped that goodness was exempt from scientific analysis, but Hamilton’s theory seemed to demonstrate otherwise. Price went through the mathematics in the model and realised that Hamilton had underestimated the power of his own theory.
“George Price had hoped that goodness was exempt from scientific analysis”
While working with Hamilton on kinship and altruism, the atheist Price underwent a religious epiphany. In an irony that turns the debate about religion and evolution on its head, Price believed that his findings on altruism were the result of divine inspiration. He became a devout Christian, donating most of his money to helping the poor. At various times he lived as a squatter; at other times he slept on the floor at the Galton Laboratory of University College London, where he was working. Price lived the life of the altruists that he had modelled mathematically.
Since Hamilton published his model, thousands of experiments have directly or indirectly tested predictions emerging from his rule, and the results are encouraging. Hamilton’s rule doesn’t explain all the altruism we see but it explains a sizeable chunk of it. With time, Hamilton himself began to realise the power of his model, as well as its implications, and was somewhat dismayed that altruism could be boiled down to a simple equation: “I like always to imagine that I and we are above all that, subject to far more mysterious laws,” he noted in volume 1 of his book Narrow Roads of Gene Land. “In this prejudice, however, I seem, rather sadly, to have been losing more ground than I gain. The theory I outline… has turned out very successful. It… illuminates not only animal behaviour but, to some extent as yet unknown but actively being researched, human behaviour as well.”
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Lee Alan Dugatkin is a biologist at the University of Louisville, Kentucky. His most recent book is The Altruism Equation: Seven scientists search for the origins of goodness (Princeton University Press, 2006).
