There's an excellent article over at the New York Times on what factors are contributing to the evolution of the human brain. Specifically, neuroscientists Sam Wang and Sandra Aamodt ask whether it can be said that we're becoming more intelligent, based on the evidence we currently have. They say:
It used to be believed that people had a level of general intelligence with which they were born that was unaffected by environment and stayed the same, more or less, throughout life. But now it's known that environmental influences are large enough to have considerable effects on intelligence, perhaps even during your own lifetime.