It is a puzzle of evolution: If natural selection dictates that the fittest survive, why do we see altruism in nature? Why do worker bees or ants, for instance, refrain from competing with those around them, but instead search for food or build nests on behalf of their companions? Why do they sacrifice their own reproductive success for the good of the group?
In the 1960s, British biologist William Hamilton offered an explanation in a theory now called kin selection. When animals, often insects, help siblings or other relatives survive, they are enhancing the odds that their shared family genes will be passed on. In other words, the genes, not the individual or social group, are what counts in evolution.
Hamilton’s idea was eventually accepted by most biologists, and found an enthusiastic backer, at the time, in Edward O. Wilson, the renowned Harvard evolutionist.
That was then. Now, Wilson has changed his mind, startling colleagues by arguing that kin selection does not lead to altruism.
Kin selection is a scientific crutch, a “very seductive” idea that “doesn’t tell us anything decisive about how altruism originated,” Wilson says. He adds: “We need a whole new way of explaining things.”
He has one. Wilson posits that altruism evolved due more to ecological circumstances than the influence of genes.
In his new book “The Superorganism,” out today, Wilson and his co-author, Bert Holldobler, argue that natural selection operates on the group, not just the gene. The lavishly-illustrated volume examines the complex systems that help insect societies survive, from an intricate array of communication signals to the elaborate architecture of nests. But Wilson - though not Holldobler - goes further, saying altruism occurs not because animals share family ties, but because certain altruistic acts have become useful for the overall survival of insect groups.
“The close kinship of the members of these groups is a consequence, not a cause, of their evolution,” says the ever-genial Wilson in an interview at his home in Lexington. He believes altruistic (or eusocial) societies developed in ecological conditions where food was plentiful enough to allow insects to practice “progressive provisioning,” in which a mother leaves its offspring with food, as some wasps or bees do. This creates a need for others in the insect society to stand guard over the young.
Given these conditions, Wilson postulates, an insect group experiencing a single beneficial genetic mutation - such as the ability to distinguish nest mates from outsiders, a trait many insects possess - might adopt altruism as a useful social behavior.
Many biologists emphatically disagree.
“I have enormous respect for Wilson, he’s a huge figure in the field of social evolution and beyond,” said Andrew Bourke, a biologist at the University of East Anglia, in England. “But I just think he’s got it wrong in this case. Kin selection is the leading theory we have for why animal societies are why they are, and the evidence for it is very strong.”
Other scientists profess surprise because Wilson staunchly backed kin selection in the 1960s and 1970s. “We would all like to know what’s going on with Wilson,” says Francis Ratnieks, a biologist at the University of Sussex, also in England. Even Holldobler, a biologist at Arizona State University who says he and Wilson agree on “95 to 98 percent” of their work, continues to accept the kin-selection theory.
Those who disagree with Wilson suggest he is burdening kin selection with claims it does not make, then saying the theory comes up short. “Kin selection theory never said relatedness was the sole cause of eusocial evolution,” argues Bourke. “But it is a necessary precondition.”
In a study published in “Science” in May, four researchers (including Ratnieks) found eight separate instances in natural history when altruism developed, leading to the evolution of more than 250 altruistic species. All eight times, the reproducing females had single male partners, meaning the group largely consists of very close relatives as the kin-selection theory predicts.
In response, Wilson argues the paper’s authors “didn’t have a control” - studying closely-related species that do not become altruistic.
But kin selection advocates say they already believe that highly related groups do not always produce altruism. “There must have been some other factors,” said Ratnieks, agreeing that ecological circumstances surely played a role.
For his part, Wilson remains open to discussion. “I would hate to treat this as a closed subject,” he says.
But why is Wilson revisiting it?
Wilson says that reviewing the work in the field simply left him skeptical of kin selection theory. But his next project is a study of human sociability, which he thinks may also defy traditional kin-selection analysis. “It’s comforting to believe our deep concern for kin must be fundamental to our existence,” says Wilson. “And it might turn out to be the case. But maybe we should look at non-kin bonding more closely, such as a brave soldier who throws himself on a grenade to save a squad.”
Wilson’s intellectual style is one of grand synthesis, linking species and academic disciplines, and he may prefer an explanation of altruism that spans the living world.
Besides, Wilson enjoys an old-fashioned scrap - bringing to mind one of the many vignettes in “The Superorganism.” The book describes how, in India, ants of the harpegnathos saltator species often engage in public duels: A pair at a time, they use their antennae to lash and charge each other. Eventually both ants walk away, usually unscathed.
Holldobler and Wilson write that its duels “may serve as a positive feedback loop,” raising ant fitness no matter who wins. Perhaps the same applies to evolutionary biology.
