Most scientists agree that the major human brain structures and their principle subdivisions are tightly controlled by genes. But this need not be true of the functionally specialized circuits that adults use to solve many cognitive problems. Much cognitive development occurs through "proliferation and pruning," as neuroscientists have called the process: That is, an initial overabundance of neurons and connections are whittled down in response to environmental stimuli and to the brain's own activity. As cells compete with each other, some connections are lost. This is a good thing, essential to mental maturity.

As Buller explains, the pruning process can result in "information process structures" that may resemble the modules postulated by EP. But they are "environmentally shaped, not genetically specified outcomes of development." In other words, the human brain evolved to be plastic in important ways, and its ability to reorganize brain circuits and to learn is a biological adaptation.