CogniFit's Science blog: Male Brains And Female Brains: Nature Or Nurture?

Male Brains And Female Brains: Nature Or Nurture?

Scientists have established that there are definitely anatomical differences between male and female brains.

Now the question remains to understand if these differences in the brain are the result of the distinct behavior of male and female (nurture) or in the contrary that these differences provoke the difference in behavior (nature).

Using sophisticated MRI scanning, Peg Nopoulos, Jessica Wood and colleagues at the University of Iowa have been trying to shed light on the nature vs. nurture conundrum.

Females of all ages are better at recognizing emotion or relationships than are men. These sex-determined differences appear in infancy and the gap widens as people mature. When such differences appear early in development, it can be assumed that these differences are programmed into our brains, “hard-wired” to use a computer analogy.

Sex differences that grow larger throughout childhood however, are probably shaped by culture, lifestyle and training. Studies of brain plasticity have shown us that experience changes our brains structure.

Initial research showed that an area of the brain, the straight gyrus (SG), involved in social cognition and interpersonal judgment was about 10% bigger in women than in men (men’s brains are about 10% larger than women’s brains, so measures were proportional). In addition, the size of the SG also correlated with a test of social cognition, so that people who scored higher in interpersonal awareness, male or female, had larger SGs.

Scientists hypothesized that perhaps evolution accounted for the difference. Since women have to raise children, they needed to be more sensitive nurturers. Perhaps prenatal hormones effect the development of the SG as well. So, the next step was to see if the size difference held true in children as well.

When children between the age of 7 and 17 were examined, the results were exactly the opposite. The SG was larger in boys! The same interpersonal skills test showed that the better the person was in interpersonal skills, the smaller the SG was. Again just the opposite of what was found in adults.

Then the researchers performed another test. They divided the subjects not just by biological sex; they also gave each subject a test of “psychological gender,” a questionnaire that assesses masculine and feminine traits, regardless of biological sex. These correlations were the same. Masculine children had a larger SG but feminine adults had the larger SG.

So while there may be actual physical differences in men’s and women’s brains, these differences may not be totally “hard-wired.” Masculine and feminine traits are more influenced by rearing and experience than by biological sex. Their brains must be molded by their experiences as a boy or girl at least to some degree.

Do women have larger SGs because they belong to a group that practices being more sympathetic and nurturing or are they more nurturing and sympathetic because their SGs are bigger? There is no clear cut answer, but the research is definitely challenging the idea that behavior is simply a factor of X and Y chromosomes.