Lise Eliot set out to write a book that would chart how the brains of boys and girls develop differently. But when the Chicago-based neurobiologist reviewed the scientific literature, she found surprisingly little evidence of sex differences in the developing brain.
In her new book, Pink Brain Blue Brain , Dr. Eliot argues that brains are shaped by how kids spend their time - playing with dolls versus balls - and that small, innate differences become amplified over time by parents, teachers and immersion in boy or girl culture. The following interview has been edited and condensed.
So girls aren't from Venus and boys aren't from Mars?
So much that has been talked about in terms of brain differences between boys and girls is based on studies of adults. There just isn't the data in children, or the data we have so far doesn't reveal anything dramatically different between boys' and girls' brains. I want to be clear I am talking about their brains. There are obviously pretty striking differences in behaviour.
Were the differences you saw in your own children, a girl, Julia, and two boys, Sam and Toby, one of the reasons you started researching this book?
Certainly, boys and girls are different, and my children mirrored the play differences that have been well described. My boys are and were more physically active - that is one of the more reliable differences between boys and girls.
As a parent and neurobiologist, you see this and you say, "Wow, what is different about their brains, how is that all shaped?"
It's not all about testosterone?
I'm not denying that hormonal and perhaps genetic effects shape the brain and behaviour, but what I am trying to do is bring the other side of the equation in because it has been totally overlooked for the last 25 years.
The public gets confused about this idea that brain equals nature. There are two components of our biology: nature and nurture. And 50 years of neuroscience that show how experience and environment critically shapes brain structure and function.
We have become so enamoured of genetic determinism we have lost sight that, yes, parents actually also shape children's gender behaviour - and peers and the media and culture at large.
I think people would be comfortable with the idea that boys and girls grow up in two different cultures. All you have to have to do is walk into Toys 'R' Us and see there are two different environments that tell kids where they belong.
Was there an "aha" moment when you realized that there isn't evidence that boys and girls brains are that different?
I was very frustrated that I wasn't finding more neuroscience early on to show what is different between boys' and girls' brains. That forced me to look at the adult findings, and there I was really shocked to learn that some of the adult differences we were all taking for granted were not well proven and in fact some of these findings are turning around.
First, there was the claim about the corpus callosum, this massive fibre bundle which connects our two brain hemispheres. For years, we were hearing that women have a larger corpus callusom than men. That was supposed to explain why women are better multitaskers and use both sides of the brain, while men tend to use one or the other at a time. But the public awareness was based on a very small study published in 1982 in Science that was reported in Time magazine and The New York Times. But what wasn't publicized were the follow-up studies. There are now hundreds, and when you put them together through meta-analysis, the definitive way of analyzing many studies, the effect is now insignificant. There is no longer believed to be a difference between adult men and women corpus callosums. The "aha" for me was realizing whatever sex differences there are, even in adults, are very, very subtle.
If they are subtle in adults, they are likely to be even more subtle in children before all this social learning takes place.
What other findings have led to the notion that boys and girls have very different brains? You mention in your book that many people focus on differences between when boys and girls start to speak. But the typical girl says her first words only a month before a typical boy.
Part of the confusion comes from the fact that people tend to see something in black in and white - if there is any difference at all, we magnify it into this Mars-versus-Venus kind of gap.
When you look at when children begin speaking, and you look at the data on these differences, you see there is only a one-month gap. Yet a lot of parents have the perception that it is a bigger gap. There is a danger in that. If a boy is not speaking much by the age of 2 - when he should be stringing words together into mini-sentences - sometimes they will hear from teachers or pediatricians not to worry: "He is a boy, boy talks later." In fact, we know that the earlier you address speech and language problems the more successful the therapy. There is a real danger in exaggerated sex differences.So what are the differences between the brains of boys and girls?