In December, a highly publicized study declared that distinctive wiring in the brain explains different skill sets in men and women. After scanning hundreds of participants’ brains, the researchers reported that men have stronger connections within a given hemisphere, whereas women have stronger connections between the two. This makes sense, they speculated, because same-side connections are responsible for carrying out focused tasks, such as map reading, at which men excel, whereas cross-brain connections underlie the multitasking and social graces that are most often associated with women. Finally, evidence that men are from Mars and women are from Venus! The trouble is, the study is riddled with faulty assumptions and methodological flaws. Worse still, problems like these taint just about every study that claims to show a “hardwired” explanation for why men and women behave differently.
In 1854, German anatomist Emil Huschke reported that the brain’s frontal lobe, which he called the “brain of intelligence,” is larger in men than in women. (Scientists of this era made comparable proclamations about race, claiming, for instance, that the frontal lobe is smaller in “Negros” than in Caucasians.) Today’s neuroscientists are doing something similar: using new technologies to unwittingly perpetuate stereotypes that are just as unfounded and just as damaging.
In the past decade, several thousand papers have been published on sex differences in the human brain. Many physical differences are genuine, but oftentimes not meaningful. Take for example, an easily measurable characteristic: size. One study recorded men’s brain volumes at 1,053 to 1,499 cubic centimeters and women’s at 975 to 1,398. The overlap means you couldn’t tell the sex of a random brain from its size.
In addition, many supposed psychological differences between the sexes are as illusory as the physical ones. In 2005, Janet Hyde, a researcher at the University of Wisconsin-Madison, analyzed data from studies of apparent sex differences in traits such as aggression, social ability, math, and moral reasoning. Nearly four fifths of the traits showed only a minor or negligible difference between men and women.
In the rare cases where actual psychological differences exist, they cannot be attributed to innate neurology alone. Everything in the brain is a combination of nature and nurture. Culture comes into play, which affects behavior, which then affects the brain. From birth (and even in the womb), a baby is labeled as a girl or boy and treated a certain way as a result. For example, a 2005 study of 386 birth announcements in Canadian newspapers showed that parents tend to say they’re “proud” when it’s a boy and “happy” when it’s a girl. Anne Fausto-Sterling, a biologist at Brown University, has shown that mothers talk to infant girls more than infant boys. This could partly explain why girls tend to have better language skills later on.
“Some differences end up fairly entrenched in adult human beings,” Fausto-Sterling says. “But that doesn’t mean that you were born that way or that you were born destined to be that way.”
This article originally appeared in the April 2014 issue of Popular Science.