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...
But in the latest issue of the journal Nature, a team of prominent evolutionary biologists at Harvard try to demolish the theory.
Dr. Hamilton argued that since we share half of our genes with our siblings, sometimes we can pass on more copies of our genes by helping our relatives survive and have offspring than we could if we had children ourselves.
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.
Dr. Hamilton called his theory inclusive fitness and published it in 1964. Since then, biologists have used the theory to explain how animal societies, such as bees and ants, evolve. It has even been applied to our own evolution.
However, a team of biologist from Harvard has cast doubt on Hamilton's theory.
The scientists argue that studies on animals since Dr. Hamilton’s day have failed to support (inclusive fitness). 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.”
The researchers developed a mathematical analysis of natural selection to test the differences between different behaviors in a population. They tested altruism versus selfish populations. What they found didn't support inclusive fitness theory.
The researchers found that inclusive fitness theory worked only under special conditions. All the effects that the animals had on each other had to take place on a one-to-one basis. In the real world, individuals may benefit from many other individuals as a group.
Standard natural selection, the scientists argue, explains everything inclusive fitness theory was supposed to, without these special conditions.
However, many scientists disagree with those findings and still back inclusive fitness theory. They argue that the study is flawed. It doesn't include how closely the animals are related, and therefore kinship can't be ruled out as a driving force in social evolution.
“This paper, far from showing shortcomings in inclusive fitness theory, shows the shortcomings of the authors,” said Frances Ratnieks of the University of Sussex.
The supporters of inclusive fitness theory are sending a reply to Nature to challenge the Harvard researcher's paper.
This is what I love about science. A vigorous debate is going on about the details of a larger theory. I have no idea which side will end up being correct, but I'm positive that scientists will weigh all the evidence and follow where it leads them. While I'm sure this news story will show up on some creationist's blog about how scientists are disagreeing over evolution, this in no way voids Darwin's theory. It only makes the theory richer and more subtle.