Scientists Square Off on Evolutionary Value of Helping Relatives
By CARL ZIMMER
Why are worker ants sterile? Why do birds sometimes help their parents raise more chicks, instead of having chicks of their own? Why do bacteria explode with toxins to kill rival colonies? In 1964, the British biologist William Hamilton published a landmark paper to answer these kinds of questions. Sometimes, he argued, helping your relatives can spread your genes faster than having children of your own.
For the past 46 years, biologists have used Dr. Hamilton’s theory to make sense of how animal societies evolve. They’ve even applied it to the evolution of our own species. But in the latest issue of the journal Nature, a team of prominent evolutionary biologists at Harvard try to demolish the theory.
The scientists argue that studies on animals since Dr. Hamilton’s day have failed to support it. The scientists write that a close look at the underlying math reveals that Dr. Hamilton’s theory is superfluous. “It’s precisely like an ancient epicycle in the solar system,” said Martin Nowak, a co-author of the paper with Edward O. Wilson and Corina Tarnita. “The world is much simpler without it.”
Other biologists are sharply divided about the paper. Some praise it for challenging a concept that has outlived its usefulness. But others dismiss it as fundamentally wrong.
“Things are just bouncing around right now like a box full of Ping-Pong balls,” said James Hunt, a biologist at North Carolina State University.
Dr. Hamilton, who died in 2000, saw his theory as following logically from what biologists already knew about natural selection. Some individuals have more offspring than others, thanks to the particular versions of genes they carry. But Dr. Hamilton argued that in order to judge the reproductive success of an individual, scientists had to look at the genes it shared with its relatives.
We inherit half of our genetic material from each parent, which means that siblings have, on average, 50 percent [1/2] of the same versions of genes. We share a lower percentage with first cousins [1/8], second cousins [1/32] and so on. If we give enough help to relatives so they can survive and have children, then they can pass on more copies of our own genes. Dr. Hamilton called this new way of tallying reproductive success inclusive fitness.
Each organism faces a trade-off between putting effort into raising its own offspring or helping its relatives. If the benefits of helping a relative outweigh the costs, Dr. Hamilton argued, altruism can evolve.
The idea wasn't exactly wholly new. J.B.S. Haldane liked to joke in the 1950s when he was asked if he'd give up his life for his brother: No, but maybe for 2 brothers or 8 first cousins.
Dr. Hamilton believed that one of the things his theory could explain was the presence of sterile females among ants, wasps, and some other social insects. These species have peculiar genetics that cause females to be more closely related to their sisters than to their brothers, or even to their own offspring. In these situations, a female ant may be able to spread more genes by helping to raise her queen mother’s eggs than trying to lay eggs of her own.
"Impossible, I thought, this can't be right. Too simple… By dinnertime, as the train rumbled on into Virginia, I was growing frustrated and angry… And because I modestly thought of myself as the world authority on social insects, I also thought it unlikely that anyone else could explain their origin, certainly not in one clean stroke… By the time we reached Miami, in the early afternoon, I gave up. I was a convert and put myself in Hamilton's hands. I had undergone what historians of science call a paradigm shift."
But as the years passed, Dr. Wilson’s enthusiasm for the theory waned. “It was getting tattered,” he said. Many species with sterile females, for example, do not have the strange genetics of ants and wasps. And many species with the right genetics have not produced sterile females. ...
A number of scientists strongly disagree, though. “This paper, far from showing shortcomings in inclusive fitness theory, shows the shortcomings of the authors,” said Frances Ratnieks of the University of Sussex.
Dr. Ratnieks argues that the Harvard researchers cannot rule out kinship as a driving force in social evolution because their model is flawed. It does not include how closely related animals are.
To see some of the more interesting implications of Hamilton's theory, see my 2004 VDARE.com article.