One had to eliminate unecessary details quickly, simplify and react just as quickly. Or, if you weren't the Alpha male leader, you'd want to be one of the guys. Conformity became crucial. The converse of this is that women as gatherers had to mentally map in fine detail things like bushes and berries and where they had stored food. They also tended to relate less by competition and more by sympathy and empathy.
Research suggests that in women, the two spheres of their brains communicate better than do men's.
Studies show that women pull in information from both halves. This allows women to give a more sophisticated emotional response. Thus, women are better at talking about their emotions and reading subtleties. It therefore seems that this isn't necessarily a case of men and women being smarter or not smarter than each other. Each approach was the environmentally correct one, necessary for both men and women to survive in their assigned roles.