In "Evolutionary Psychology, A Critical Introduction" 2000,
Christopher Badcock suggests that the brin could have grown
as a result of an "arms race", which in turn depends on the
newly found fact that the limbic part of the brain is built
by genes from the father, and the neocortex is built by
genes from the mother. So the different parts of the brain
have somewhat different "interests". This is a bit complicated
to understand but is explained in this interesting book.

- Hans