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?
The one thing we know for sure is that boys' brains are larger than girls', and girls' brains finish their maturation earlier.
The maturation can have important behavioural effects. Girls mature more quickly in self-regulation, self-control, inhibiting inappropriate impulses - the kinds of things that go awry in attention deficit disorder, which girls are diagnosed with less often.
You write that these small biological differences can grow into troublesome gaps between boys and girls. Which gaps worry you the most?
The verbal literacy gap for boys is certainly a concern. Writing, in which there is a larger gap, is something we need to address.
But what I am trying to get people to focus on is that learning how to read and write, regardless of our innate wiring, are learned skills and require massive amounts of practice, practice, practice. By being aware of the roots of literacy skills - mapping speech sounds onto letters, and rhyming - we'll do much better at promoting boys' language-arts skills than we will by talking about how they are hard-wired for this and that. That's my point.
What about the idea of separate schools or classrooms for girls and boys?
This idea that boys and girls learn differently is misleading. They clearly have different interests and somewhat different needs as far as physical movement. But the idea that the process of learning how to read or do arithmetic is fundamentally different for boys and girls is wrong and probably even dangerous.
There has been a big push for single-sex schooling. I spent a lot of time looking at the research, comparing single-sex schooling to co-ed education. It's not very compelling.
It is very difficult research to do, but the data we have thus far suggest if there is an advantage, it is for girls. The largest body of data from many countries - Canada, the U.S. Britain, Australia - suggests boys do not benefit from single-gender education compared with co-ed. It leads to the conclusion that both boys and girls do better with girls in the classroom, that girls sort of settle a classroom down and provide good role models.
Is there a crisis in the education of boys?
No. Boys are not reading more poorly. But with the college enrolment gap - and look at the number of girls on honour rolls - girls are outcompeting the boys, so it looks like boys are suffering in comparison.
So what can parents do? You write that it is a good idea for parents to offer boys experiences that build literacy skills and empathy, and to give girls a chance to improve spatial skills.
Knowing that children tend to play to their strengths, I think what we can do as parents and teachers is provide the cross-training that will benefit them later on. Learning is so cumulative; everything we know about the brain says the earlier you start the more successful you will be.
If we just let boys and girls kind of free-run for the first five or six years, we are going to get in a situation where boys are struggling more with reading and writing, and girls are not getting the spatial and movement experience that is important, both for later math and science.
It doesn't show up until you get to geometry, calculus and physics, but the roots of those abilities develop early and there is ample room for improvement through practice. So, getting girls involved in spatial activities through sports, through building toys, even video games, should help. What about expressing emotion?
We need to appreciate the roles we play in emotional training. Studies have shown parents do treat boys and girls differently and react differently to emotionality.
Girls are permitted to express fear and sadness more, but we don't accept anger in our daughters, and vice versa for boys.
One thing that everyone agrees is socially learned is that boys don't cry. Young boys cry plenty. They cry just as much as girls at least to age 2 and 3, but they are definitely trained through their parents, from their peers, that boys should not express emotion.
For some boys, I think that becomes a big problem. On the other hand, girls could benefit more from this lesson. If there is one thing that predicts clinical depression, it is girls' tendency to ruminate or indulge in their feelings and share them to the point where they become negatively reinforcing.
I think our attitudes are very important, and I think that as parents have become more enamoured of the hard-wired philosophy, the Mars-Venus notion, we can't help but unconsciously treat our boys and girls more differently than if we had a more egalitarian philosophy.
Anne McIlroy is The Globe and Mail's science reporter.