The idea that men and women are fundamentally and irreconcilably different has persisted for much of human history and across nearly all societies. In the U.S., even over the past century's steady march towards gender equality, cultural assumptions have persisted that men are from Mars and women are from Venus. In scientific circles, the reasoning has gone that hormonal differences cause markedly different behavior.

But a new book by neurologist Donald Pfaff, Man & Woman: An Inside Story, argues that rigid definitions delineating distinct "male behavior" and "female behavior" are simply not valid. "Biological influences on sex differences in brain and behavior operate at so many different levels, and they interact with environmental influences in so many different ways, that rigid, stereotyped ideas about what is and is not typical male or typical female behavior have become impossible to sustain," he writes.

The Economist, in a positive review of the "meticulous and skeptical," if sometimes "technical," book, sums up Pfaff's research-backed argument.
In some ways men and women are consistently different, but the significant differences in their brains only pertain to those primitive behaviours which include mating, parenting and aggression. When it comes to higher functions—the skills that arguably make us human—the similarities outweigh the differences. On average, men and women score equally on mathematical and reading ability, for example. Reported differences in empathy, leadership and verbal fluency have all been exaggerated, according to Mr Pfaff. Where differences in these skills do exist, the causes may lie in the social context. The rise of the high-achieving “alpha girl” is in part due to social changes that have allowed girls equal access to education. The reasons why many boys perform poorly at school are complex, but partly social too.
In other words, with the exception of our more "primitive" functions, men and women are just not that different.