(That just means that certain conditions influenced some genetic strains but not others.)

Mogil and collaborators concluded that the laboratory environment plays an important role in the way mice behave, either masking or exaggerating the effects under genetic control. And since tail-flipping is such a simple behavior—basically a spinal cord reflex—it’s unlikely that the environment’s influence in this case is a fluke. More complicated behaviors would probably be even more susceptible to environmental effects, the researchers observed.

Results such as these strike me as similar to findings about how humans play economic games in different ways. Genes, environment, and culture interact to produce a multiplicity of behaviors in mice, and in people. The human race has adopted a mixed strategy for surviving in the world, with a diverse blend of behavioral types. It shouldn’t be surprising that cultures differ around the world as well, that the planet is populated by a “mixed strategy” of cultures, rooted in a mixture of influences on how behavior evolves.

A MIXED HUMAN NATURE

So what of human nature, and game theory’s ability to describe it? There is a human nature, but it is not the simplistic consistent human nature described by extreme evolutionary psychologists. It is the mixed human nature that, on reflection, should be obvious in a world ruled by game theory. Evolution, after all, is game theory’s ultimate experiment, where the payoff is survival. As we’ve seen, evolutionary game theory does not predict that a single behavioral strategy will win the game. That would be like a society populated by all hawks or all doves—an unstable situation, far from Nash equilibrium. Game theory’s rules induce instead a multiplicity of strategies, leading to a diverse menagerie of species practicing different sorts of behaviors to survive and reproduce.

Seen through the lens of game theory, evolution’s role in human psychology is still important, but it operates more subtly than



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