For example, although women make up 53 percent of the U.S. population qualified by age to be members of the Senate, they don't hold 53 seats in the Senate.
Some evolutionary psychologists point to natural selection during prehistory.
For generations, males could specialize in one strategy or another to increase their chances of mating. Males running to the upper extreme in the talents required for one strategy would not need to possess more than mediocre talents for the other strategy. Hence, the male progeny of successful males inherited greater variation along each dimension than did female progeny. Meanwhile, females, whose reproductive success is thought to have depended less on high-risk strategies for catching mates than on nurturing the results of that catch, followed the less risky strategy of hugging the mean on relevant dimensions of fitness, one of which may be cognitive abilities. Whatever the cause, the differences between the sexes are visible today.