A new book by Lise Eliot, a neuroscientist at Rosalind Franklin Institute of Medicine, examines the role that very subtle differences in parents' expectations may create differences in brain development of boy and girl babies.
According to an article about Pink Brains, Blue Brains in Newsweek, many studies show that parents' expectations for gender-based behavior or competencies can lead to reinforcing those tendencies in kids.
For example, in a study where people were told that male newborns were female and vice versa, they rated the "male" babies as more irritable.
I haven't read the book, but the Newsweek article points up a bit of a contradiction. Eliot may be saying that all the differences in adult brains can be tied to differences in nurturing, but the article itself contradicts that:
For instance, baby boys are more irritable than girls. That makes parents likely to interact less with their "nonsocial" sons, which could cause the sexes' developmental pathways to diverge. By 4 months of age, boys and girls differ in how much eye contact they make, and differences in sociability, emotional expressivity, and verbal ability—all of which depend on interactions with parents—grow throughout childhood. The message that sons are wired to be nonverbal and emotionally distant thus becomes a self-fulfilling prophecy.
This makes sense, except ... we're starting with, "baby boys are more irritable than girls." If this is the case, then it implies that there is an innate difference, perhaps because of the greater testosterone in the male baby's brain and body.
I can certainly buy a theory that nurture can enhance these innate differences. But I have to agree with Michael Gurian (and a lot of science) that the differences in the amounts of testosterone and estrogen in a baby's brain guide neurodevelopment, especially in the first three years of life, when the neurons are forming connections that will last throughout our lives.
Gurian, authof of a series of excellent parenting books, including The Wonder of Boys, put out a press release saying,
It seems that most of the world already senses that boys and girls are inherently different (albeit on a vast spectrum, not stereotypes), but some people still fear this human experience, or aren't sure what to make of it. Unfortunately, these books/articles select evidence and don’t take into account brain scans and other hard science; and they extrapolate the effect of socialization on formation of gender in the brain. For instance, PBBB provides a study of children who are encouraged to climb a hill a certain way and extrapolates that because there were differences in how parents talked to boys/girls, this could somehow account for the profound differences that show on PET and SPECT scans between girls and boys' brains.
He also posts some research on his site showing gender-based differences in the brain.
This is an argument that won't be resolved any time soon. It's important for parents to think about this and do what they can not to reinforce crippling gender roles on kids of either sex. For our grown-up relationships, I still think that looking at our emotions and interactions through the lens of neurochemistry can provide insight and comfort.