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I've got a new article in the New Yorker this week about the persistent paradox of altruism. It's subscription only, but here's the beginning:
The vampire bat emerges from its cave at the darkest hour of night, after the moon has set. It flies low across the landscape, hunting by smell and sonar. Once the bat finds a victim—and it can feed on most warm-blooded animals, from songbirds to cattle—it starts stalking its prey. The bat lands silently a few feet away, then runs on its wings toward the sound of a pulsing vein. A pair of teeth sharper than a scalpel cut into the flesh. Blood leaks from the wound; the bat laps it up. Sometimes, the bat consumes its weight in blood during the night.
Although the vampire bat has traditionally been seen as a ghoulish predator, it interests biologists for a very different reason: it is deeply altruistic. The bats live in expansive colonies, with hundreds or thousands sharing the same dark cave. Bats must feed constantly—they starve to death within sixty hours—and this has led to the evolution of an unusual way of sharing food. If a vampire bat fails to find a victim during the night, it will begin licking the wings and lips of a chosen colony member. The animals then lock mouths, while the successful hunter starts vomiting warm blood. If such sharing did not take place, scientists estimate that more than eighty per cent of adult vampire bats would die of starvation every year.
Charles Darwin regarded the problem of altruism—the act of helping someone else, even if it comes at a steep personal cost—as a potentially fatal challenge to his theory of natural selection. After all, if life was such a cruel “struggle for existence,” then how could a selfless individual ever live long enough to reproduce? Why would natural selection favor a behavior that made us less likely to survive? In “The Descent of Man,” Darwin wrote, “He who was ready to sacrifice his life, as many a savage has been, rather than betray his comrades, would often leave no offspring to inherit his noble nature.” And yet, as Darwin knew, altruism is everywhere, a stubborn anomaly of nature. Bats feed hungry brethren; honeybees defend the hive by committing suicide with a sting; birds raise offspring that aren’t their own; humans leap onto subway tracks to save strangers. The sheer ubiquity of such behavior suggests that kindness is not a losing life strategy.
For more than a century after Darwin, altruism remained a paradox. The first glimmers of a solution arrived in a Bloomsbury pub in the early nineteen-fifties. According to legend, the biologist J. B. S. Haldane was several pints into the afternoon when he was asked how far he would go to save the life of another person. Haldane thought for a moment, and then started scribbling numbers on the back of a napkin. “I would jump into a river to save two brothers, but not one,” Haldane said. “Or to save eight cousins but not seven.” His drunken answer summarized a powerful scientific idea. Because individuals share much of their genome with close relatives, a trait will also persist if it leads to the survival of their kin. According to Haldane’s moral arithmetic, sacrificing for a family member is just a different way of promoting our own DNA.
Haldane never expanded his napkin calculations into a formal mathematical theory. That task fell to William Hamilton, a young graduate student at University College London. He struggled for years on the project, often working late at night on a bench in Waterloo Station, where the commuting crowds eased his loneliness. In 1964, he submitted a pair of papers to the Journal of Theoretical Biology. The papers hinged on one simple equation: rB > C. In other words, genes for altruism could evolve if the benefit (B) of an action exceeded the cost (C) to the individual once relatedness (r) was taken into account. The equation confirmed the truth of Haldane’s joke: once kinship was part of the calculation, altruism could be easily explained in genetic terms. Hamilton referred to his model as “inclusive fitness theory,” since it expanded the Darwinian definition of “fitness”—how many offspring an individual manages to have—to include the offspring of surviving relatives. The math seemed to solve the biological problem, but in doing so it opened up a moral problem: altruism, it suggested, isn’t really altruistic at all, but rather just another means of spreading our genes. Instead of having sex, we’ve saving kin.
At first, Hamilton’s concept of inclusive fitness was entirely ignored. Many biologists were turned off by the math, while few mathematicians were interested in the problems of biology. The following year, however, an ambitious Harvard entomologist named E. O. Wilson read the paper while taking an eighteen-hour train ride from Boston to Miami. “I had nothing else to do, so I caught up on all my old journals,” Wilson told me recently when I visited him at his Harvard office. “When I began reading Hamilton’s paper, my first response was that the equation was way too short. I thought, There’s no way it can be this easy. But then I reread the paper. And then I read it again. And that’s when I got jealous.” Wilson wanted to understand the altruism at work in the ant colony, and he became convinced that Hamilton had solved the problem first. To further the cause of inclusive fitness, Wilson began writing about the idea in a series of influential articles and books, introducing the startling logic of Hamilton’s equation to biologists. “I really became an evangelist for the idea,” Wilson says. “And this was not an easy idea to sell. Nobody wanted to believe that one equation could explain altruism. Eventually, though, people saw that we were right. I won that argument decisively.”
By the late nineteen-seventies, the work of Hamilton was featured prominently in textbooks; his original papers have become some of the most cited in evolutionary biology. As Wilson first realized, the equation allowed naturalists to make sense of animal behavior using genetic models, giving the field a new sense of rigor. “Before Hamilton, there were different explanations for every species,” Wilson says. “There was no overarching theory, nor was there any way to connect what we saw in the field to what we were learning about genes in the lab. Hamilton helped solve both those problems.” In fact, inclusive fitness theory solved those problems so well that it was soon applied to biological traits completely unrelated to altruism, such as the evolution of homosexuality, of tribal violence, and of alarm calls. In an obituary published after Hamilton’s death, in 2000, the Oxford biologist Richard Dawkins referred to Hamilton as “the most distinguished Darwinian since Darwin.”
But now, in an abrupt intellectual shift, Wilson says that his embrace of Hamilton’s equation was a serious scientific mistake. “I’m going to be blunt: the equation doesn’t work,” he says. “It’s a phantom measure. It can’t explain nearly as much as people think it can. Back when I first read Hamilton, inclusive fitness seemed to make sense of so many different mysteries. But now we know more. And I’m not afraid to admit I was wrong.” Wilson’s apostasy has set off a scientific furor. The vast majority of his academic colleagues are convinced that he was right the first time, and that his recantation has damaged the field. There have been nasty denunciations in the press and signed group letters in prestigious journals; some have hinted that Wilson, who is eighty-three, should retire. The controversy is fuelled by a larger debate about the evolution of altruism. Can true altruism even exist? Is generosity a sustainable trait? Or are living things inherently selfish, our kindness nothing but a mask? This is science with existential stakes.
