Considerations of [causal fallacy] are especially important to keep in mind when on the topic of brain science because so little is understood or recognized about the possibilities of the brain. When a researcher notices that one particular group of people exhibit a neurological difference, such as increased neurons in a specific region, from the control group, the researcher is not necessarily at liberty to say (beyond the vaguest conjecture) what the cause of the observed difference could be. It is known that patterns of brain activity can alter the physical structure of the brain, especially in childhood. Therefore, nature versus nurture arguments become very precarious and downright dubious.
Women may, on average, have more neurons than men in the such-and-such region of their brains because in reality that region is used in decisions involving food preparation (such as what smells fresh or spoiled or how salty the sauce should be) and women are more often required to develop culinary aptitude in our society. Of course, this is just for example sake, and not necessarily true: accentuating stereotypes can help elucidate arguments. Or men may, on average, have a larger such-and-such region of the brain because that region facilitates understanding of projectile motion that men need to play certain sports (my high school geometry teacher actually told the class that it was postulated that athletes tend to have an easier time learning geometry than non-athletes because of the subconscious spacial reasoning that needs to develop in order to correctly model the trajectory of an object, such as a basketball)*. What these two examples have in common is that they have nothing whatsoever to do with genetics or evolution or nature. Instead, the differences in brain structure are entirely produced by behavior.
However, in our ignorance we might assume that observed brain differences between genders are clearly the result of DNA. And we might even go on to build a false assumption upon a false assumption and conclude that these brain differences manifest in gender specific tendencies and stereotypes, such as women being more empathetic, talkative, and socially dependent, and men being hyper-sexual, risk seeking, and more rational than emotional. I should now have given you the perspective to see through this kind of fallacy and realize that such notions are, at best, highly questionable and much, much more complex than what even the most penetrating current research can skim the surface of.
Of course, some genetically based theories on gender differences may be true. Certainly biology plays some degree of a role in gender specific behavioral differences. The problem is not about what is true versus what isn’t true. The problem is that so many people (such as Dr. Louann Brizendine) seem to want to jump on the old biology bandwagon and assume that genetics is the cause of everything because such ideas seem so convincing and fashionably scientific. But if you assume you know what makes a human being do the things that a human being does, then you tacitly claim that you know everything about the working of the mind. Considering that the mind is basically the most complex thing ever encountered in human experience, it takes a lot of gall to even suggest that DNA is most likely responsible for certain trends in human behavior. At our current level of scientific understanding, there are simply too many variables unaccounted for to trace a linear relationship between a biological element and a high-order** behavioral element.
*(Consider an NFL quarterback: he must figure out how to place a spiraling football into the arms of a runningback who will run straight about 20 yards, then cut diagonally left for about 15 more yards. The QB is himself jogging backwards and in erratic directions to avoid the enemy linebackers. His target runningback is far away from him now, obscured by other players, and moving at a velocity contrary to his own. He must make sure that the football flies over the heads of enemy team members so that it is not intercepted, and he must place the ball level with the runningback’s torso. Too high and it might slip from his fingers; too low and it might fumble. He must correct for even the slightest lateral or parallel wind, and he must watch that his feet don’t slide on the grass, especially in rain or snow, when his massive arm finally launches the ball. Considering that he only has a couple of seconds to decide on a target and fire before clobbered by the opponents, it’s a pretty extraordinary mental feat. So it’s not unreasonable to imagine that he might have been keener at imagining spacial translations in his mind than his geometry classmates, having had more practice doing so on the field.)
**(By “high-order” I mean a behavior that is affected by and reliant upon a complex array of conscious experiences and decisions. A “low-order” behavior would be the opposite: a behavior that is fairly unconscious. For example, putting your hands over your head and flinching because a bomb goes off in your vicinity would be a low-order behavior. It is largely instinctual and not a lot of thought goes into it. On the other hand, deciding to leave your husband and run off with some Colombian surfer would be a high-order behavior. Presumably a sizable amount of thought went into the decision (it was not just instinctual or instantaneously hedonistic), and one could possibly trace the reasons for such a decision back through thousands of different events over her life and childhood that put her in such a state as that which enabled her to make the decision to leave. Maybe a hormone can have pretty strong and predictable effects over a low-order behavior, but over a high-order one? (See bullet #1 in Pseudoscience: Misunderstanding, Misrepresentation, Misattribution, Predisposition))