Darwin himself suggested a solution to the altruism problem, a solution that today we call group selection. The idea is that natural selection operating on individuals is a less powerful force than another form of selection that operates on groups. Consider two groups, one with individuals that are altruistic, helping one another out, and another with individuals that act entirely selfishly. Darwin argued that, in a conflict between the two groups, the first group would beat the second because the first group works better as a unit. Here, then, we see that selection in favor of altruism that benefits the group has trumped selection in favor of selfish behavior.

Although an attractive idea, group selection is probably not important in the evolution of altruism. Altruism under group selection is typically not an evolutionarily stable strategy, meaning that this kind of behavior can be readily driven to extinction by an alternative strategy. It used to be thought that lemmings, a species of Scandinavian rodent, would collectively kill themselves by plunging into the ocean when the population became too large to sustain. This self-sacrificial, altruistic act would ensure that the population did not exhaust available resources and would prevent a population crash.

This is a nice story, but untrue. Lemmings do not in fact commit suicide; they take to the water to swim to new territories during migration. And we can see the evolutionary logic prohibiting the evolution of such altruistic behavior. An individual that “cheats” by not performing the altruistic act will survive and breed, and its altruistic companions will not. Now consider that this behavior—to kill oneself or not—is genetically encoded. A mutation that arises in a population that causes the individual to “cheat” and not kill itself will spread rapidly through the population by natural selection until, after many generations, it has completely replaced the altruistic allele that causes the individual to kill itself. The lemming behavior, then, is not an evolutionarily stable strategy because natural selection favors an alternative strategy.

This description is oversimplified because there is unlikely to be a simple genetic basis to traits such as these, but the point stands: Group selection is in general not an evolutionarily stable strategy because it can readily be overthrown by “selfish” strategies.

Quick Check 4 It’s sometimes said that the reason an animal does something is that it’s “for the good of the species.” Why is this argument incorrect?