Conceptions of the human brain range from the blank slate to a
strongly modular structure produced by adaptations to problems
our ancestors encountered in African savannas. Metaphors and
models can help us formulate hypotheses about the level of
constraining structure built into the brain. Here I discuss
David Sloan Wilson’s use of the immune system as a model for
human cognitive flexibility. The immune system has evolved to
cope with the challenges posed by disease-causing organisms that
are highly diverse, short-lived, and rapidly evolving. I argue
that this model is not a good guide to the kind of cognitive
structure that has evolved in response to challenges from more
stable features of the ancestral environment, for instance,
coping with large predators and hostile conspecifics or finding
and selecting food. Metaphors, Models, and Modularity Few
scientists doubt that evolved human traits are the result of the
same processes that generated the great diversity of life on
Earth. Most scientists agree that n