Twistermind: The brain has been extensively studied but is still poorly understood. Before the study that spawned the article that I linked there was also a review that tested the strength of categorizing people based on gender in scientific studies of the brain.
This is common practice but that does not mean it is well supported, the study that tested the strength of the categorization also found greater variability within groups based on gender than between groups which suggests that gender is a poor factor for categorization of neurobiological anatomy and function.