For decades, psychologists and researchers have been telling us the same old thing — boys and girls are fundamentally different. Their brains are different, their childhood development is different, their perceptions of the world around them are different. It’s the old nature versus nurture debate, with many parents unmistakably believing that nature is the primary force in a child’s development and that all parents can do is hang on for the ride.

But a new book by Lise Eliot, PhD, suggests that many of these differences are what we, the adults, make of them. She’s done the equivalent of a meta-analysis on the research foundation for gender differences between boys and girls, and put into a consumer-digestible format. The results are summarized in her new book, Pink Brain, Blue Brain: How Small Differences Grow Into Troublesome Gaps — And What We Can Do About It. As Newsweek summarized:

How we perceive children — sociable or remote, physically bold or reticent — shapes how we treat them and therefore what experiences we give them. Since life leaves footprints on the very structure and function of the brain, these various experiences produce sex differences in adult behavior and brains — the result not of innate and inborn nature but of nurture.

The gist of her findings is that many of the differences that parents believe are innate or nature-led are not. Motor skills? The same. Ability to have deep emotional feelings? The same. Aggressiveness? The same. Why do we observe such differences in little boys and girls? Because parents often unconsciously reinforce the gender stereotypes within their children —

“Oh, little Sally can’t run as quickly as little Bobby.”

“Oh, Mikey is always so aggressive; Angela is an angel in comparison!”

“Since little Eric doesn’t seem to express many emotions, he must not be as emotional as little Hannah, who has an outburst at the drop of a hat!”

Our children become a self-fulfilling prophecy — they turn into the kids we, by and large, imagine them to be. Parents don’t usually do this consciously, of course. It is the stereotyped roles hammered into us at an early age, reinforced by consumerism and toy makers and commercials, and our own mothers and fathers. Boys are athletic and competitive, while girls are less so, and more social and emotional. These are stereotypes we imprint on our children; they are not naturally this way.

There are some differences the research supports with robust data. Dr. Eliot found that girls write better and more easily than most boys, and that boys have a better sense of spatial navigation than girls (like in reading a map).

And hormones affecting our ability to think and reason and be in control of our emotions? The evidence was far weaker than Dr. Eliot had imagined:

On the other hand, I was surprised at how weak the evidence is for hormonal effects on our mood and thinking abilities. While prenatal testosterone has some pretty dramatic effects on play behavior and, probably, later sexual orientation, the sex hormones that rise at puberty and remain elevated in adults have surprisingly modest effects on our thinking — except for the increased sex drive that testosterone produces in both men and women.

What Dr. Eliot is saying isn’t really new. We’ve known for years that infant brains are extremely malleable. But she’s put it into simple language and has done a good job summarizing the vast body of research to really help put all of that data into some context. Her argument that small differences at birth become amplified over time as we all work to reinforce the gender stereotypes resonates.

Children must learn to stray from their comfort zones, with parents helping them try new things and explore new ways of expressing themselves that perhaps don’t feel natural at first, but will often come with time. Boys, for instance, should be encouraged and reinforced for being able to express their feelings. The book not only goes into what few differences really exist, but also explains what parents can do to help encourage their kids to go outside of their comfort zones.

It’s a timely book, and one that I look forward to reading.

Read the “Time Out New York” interview with the author: Interview with Lise Eliot for Pink Brain, Blue Brain

Read the Newsweek article: Pink Brain, Blue Brain