How Kin Selection Works

On the surface, the theory of kin selection makes a heck of a lot of sense. If natural selection is designed to weed out traits that lower reproductive success, then how do we explain the existence of altruistic traits that reduce reproductive fitness to zero? Kin selection explains that those traits are passed on through close relatives who share much of the same genetic material and have more babies thanks to the help of the altruists.

But what if we're focusing too much on the individual? Sure, altruistic behavior like guarding another bird's nest or collecting food for the queen may reduce the reproductive fitness of the individual bird or bee to zero, but what if it raises the net fitness of the whole group?

Darwin himself, in 1871's "The Descent of Man," first postulated the idea of group selection. Under this theory, altruistic traits are passed on if they increase the reproductive capacity of the group. Blood relations had nothing to do with it. Darwin explained it using the notion of self-sacrifice. Tribes of apes that exhibited unselfish and self-sacrificing behavior as a whole would defeat rival groups that looked out only for themselves, thus passing on those "nobler" genes [source: Okasha].

In fact, group selection was the prevailing solution to the problem of altruism before kin selection came along. The strength of the kin selection argument, it turns out, isn't theoretical but mathematical. Hamilton and his colleague Maynard Smith proved — using complex mathematical simulations — that simple group selection didn't have the evolutionary strength to result in the continued persistence of altruistic behavior generation after generation.

Complicating the argument is the fact that in nature, many tight-knit social groups are also composed of close relatives. Where does kin selection end and group selection begin? The debate rages on today. The distinguished Harvard biologist Edward O. Wilson, one of the earliest proponents of kin selection, co-authored a 2011 article in Nature claiming that kin selection was bunk and he had the math to prove it. He went on to say that group selection happens in humans [source: Neyfakh].

The 85-year-old Wilson was blasted by his peers, but his adamant stance is proof alone that Darwin's revolutionary ideas are still making waves more than 150 years later.

Author's Note: How Kin Selection Works

When talking about the "rules" of natural selection and evolution, we tend to hold ourselves separate from the rest of nature. Altruism in animals might be blindly motivated by group preservation, but self-sacrificing behavior in humans is different, right? It's moral, ethical, noble or just plain nice. But what if we're more driven by our genes than we'd like to think? What if we only act kind and selfless in order to raise our attractiveness as a mate? Evolutionary biologists have a name for that, too — reciprocal selection. I'll scratch your back if you'll scratch mine. I'll protect your nest this year, if you protect mine next year. There's no doubt that much of our behavior is an expression of our deep biological urges to survive and reproduce, but I like to think that we also have the capacity to sacrifice and serve without thought of reward, other than it feels really good.

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