Lise Eliot, associate professor of Neuroscience at The Chicago Medical School, outlines biological differences in girls and boys from womb to playground, explaining the crucial role that culture plays.
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Lise Eliot on Womb Gender Differences Question: What are the differences between boys and girls in the womb? Well, not a lot. You know, actually, we have a lot of data given the number of mothers who undergo ultrasound now. And although I think parents, a lot of parents, believe that boys are more active prenatally, in fact, the existing data don’t really support that. Some studies do see higher activity levels in boys before birth but others see no difference. And we even see higher activities in girls. So we definitely know boys are more active by about two years of age or even one and a half but before birth it’s not quite apparent. Probably the biggest difference between boys and girls we know before birth is that boys do seem to develop a little bit more slowly. Maybe a week or two less mature by the end of a 40 week gestation. And that actually is a problem for babies who are born premature. It’s pretty well known in the neonatology world that premature boys have much higher risks than premature girls even in terms of basic survival. So something about the Y chromosome or the cascade of hormones that it triggers does seem to slow the male development a little bit that affects boys. But behaviorally there isn’t a whole lot that jumps out at you. Question: How do boys and girls differ in early development? Yes, in some ways and not in others. And so, it’s not really possible to say, you know, girls mature more quickly than boys. Yes, in some ways they do but not in every way. And, you know, the brain has lots of different circuits, a lot of different abilities, and there’s not a single pattern for male versus female development. Boys definitely are slower to develop in terms of language. This has been known for some time. But to put numbers on it, there’s about a one month difference between girls and boys in terms of the number of words they speak. So at 20 months of age, a little girl may have a vocabulary of a couple hundred words and a little boy may have a vocabulary of 30 or so fewer words. And then he’ll catch up by a month and so on. In some ways the boys, when we talk specifically about verbal skills, they don’t ever fully catch up. This is one of the gender differences, you know, in verbal skills that we see even in adults. Although this notion that women speak 20,000 words a day and men speak 7,000 words a day is just, sort of, an urban myth that I hope is finally been debunked. The verbal differences and almost all of the cognitive differences are really quite small. A tenth or two-tenths of a standard deviation across the population. So they’re not as large as we tend to magnify them. Question: How much does biology influence gender differences, and how much does culture play a role? Sure. Well, there’s no question that there are innately programmed differences between boys and girls. Obviously their bodies are different. And some of those same cascades of genes and hormones we know are affecting the brain. Although we’re still years away from knowing exactly which circuit is affected in boys versus girls. But behaviorally we know that boys are more active, as I mentioned. And really one of the strongest differences that is probably hardwired, if you will, is the fascination with moving objects. And boys are definitely more interested in trucks and balls. And every parent will tell you that. And it’s true. In fact, it’s just about the largest sex difference there is. Only sexual preference itself is actually a larger difference between males and females than this difference in toy preference. It’s much larger than the verbal differences, spatial, even things like empathy and self-esteem which are areas of concern. Those differences are much smaller than the difference in toy choice. Take a three year old boy, a three year old girl, put them in a room with a choice of toys and you will see a pretty clear separation. But what’s interesting, and I like to focus on toy choice because I think on the one hand, it de
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