In 1975 Harvard biologist E. O. Wilson published Sociobiology, perhaps the most powerful refinement of evolutionary theory since On the Origin of Species. Darwin’s theory of natural selection postulated a brutal world in which individuals vied for dominance. Wilson promoted a new perspective: Social behaviors were often genetically programmed into species to help them survive, he said, with altruism— self-destructive behavior performed for the benefit of others—bred into their bones.
In the context of Darwinian selection, such selflessness hardly made sense. If you sacrificed your life for another and extinguished your genes, wouldn’t the engine of evolution simply pass you by? Wilson resolved the paradox by drawing on the theory of kin selection. According to this way of thinking, “altruistic” individuals could emerge victorious because the genes that they share with kin would be passed on. Since the whole clan is included in the genetic victory of a few, the phenomenon of beneficial altruism came to be known as “inclusive fitness.” By the 1990s it had become a core concept of biology, sociology, even pop psychology.
So the scientific world quaked last August when Wilson renounced the theory that he had made famous. He and two Harvard colleagues, Martin Nowak and Corina Tarnita, reported in Nature that the mathematical construct on which inclusive fitness was based crumbles under closer scrutiny. The new work indicates that self-sacrifice to protect a relation’s genes does not drive evolution. In human terms, family is not so important after all; altruism emerges to protect social groups whether they are kin or not. When people compete against each other they are selfish, but when group selection becomes important, then the altruism characteristic of human societies kicks in, Wilson says. We may be the only species intelligent enough to strike a balance between individual and group-level selection, but we are far from perfect at it. The conflict between the different levels may produce the great dramas of our species: the alliances, the love affairs, and the wars.
When you published Sociobiology in 1975, you faced enormous resistance, especially to the implication that human nature was genetically based. Now your colleagues are defending one of key tenets in your book—kin selection—while you try to dismantle it. What do you make of the shifting attitudes in your field? Interesting, isn’t it? But I’m not so sure I pivoted that much on kin selection in Sociobiology. If you look at the opening pages, I had a diagram showing how a future science of sociobiology would be built. Kin selection was a nice little part of it in 1975, but Sociobiology went way beyond that. It goes into demography: how groups are formed, how they compete, how communication evolves. Together with ecology and population genetics, it all formed a framework to help explain the origin of social behavior.
Yet a generation of sociobiologists built their research around the idea of kin selection. How did that happen? They were enchanted by kin selection because it appeared to have a basis in mathematics. It seemed solid and it looked good. It was glamorous.
Your new paper states that the mathematical underpinning of kin selection, called the Hamilton inequality, does not work. Why not? When analyzed to the bottom of its assumptions–when we ask under what conditions it could hold—it applies only to a very narrow set of parameters that don’t actually exist on Earth. Inclusive fitness turns out to be a phantom measure that cannot be obtained.
If inclusive fitness is wrong, how do you explain “eusociality”—when individuals reduce their ability to have offspring of their own to raise the offspring of others? It turns out that there’s only one condition that has to be reached in the course of evolution for eusociality to emerge: A mother or father must raise their young within reach of adequate resources at a defensible nest. Getting from the solitary lifestyle to one that includes a defensible nest can be done in one evolutionary step—one gene change. This turns the concept of inclusive fitness on its head, because the gene change and the social behavior came first. Kinship is a consequence of that, not a cause.
How do these ideas play out in the natural world? Let’s take the example of a bird with helpers at the nest. Supporters of inclusive fitness point to a correlation between the amount of help that the young birds give when they stay at home and how closely they are related to the parents and each other. But the young birds are looking after their extended family only until they have families of their own. By analogy, you might stay home and baby-sit for younger siblings after college, but it’s not out of a sense of kinship toward them. It’s because it makes financial sense until you find a job and move out. What these researchers unwittingly do not mention in their studies is that cases of inclusive fitness are quite unusual in an important way. Each of the bird species lives in an area where nest sites and territories are very scarce, very hard for young birds to get.