From brain size to emotional intelligence, Lise Eliot uncovers the truth behind age-old clichés.

Question: Are girls more hardwired to have deep friendships?

Lise Eliot: Well, the psychological measure that we would look at is empathy or awareness of other people’s emotion. And if you ask a man or a woman how do you feel if your friend’s puppy dies? Or how do you feel, you know, if your mother is sick? Generally, women will express greater empathy. They will say that it affects them harder. But if you test people – But that’s a subjective measure. When we test subjectively, we see a large sex difference in empathy. Presumably that reflects depth of relationships. But if you test people objectively, show them on a video screen images of faces and ask them to identify is that person expressing fear or anger or sadness, whatever, then you see a much, much smaller gender difference in empathy.

And so, you know, I think women are better at recognizing emotion but the difference is not as large as we culturally reinforce. And so girls are raised, I think, or through their peer groups to put greater emphasis on relationships. Men get there usually when they’re involved in a relationship and certainly when they become parents, the depth of emotion is no different. I site some studies in the book about imaging the parent brain after someone becomes a mother or father and you see much bigger differences between men who’ve never been fathers and fathers. Women who’ve never been mothers and mothers than you do between mothers and fathers. So it’s the experience of parenting that lights off these limbic circuits and helps you respond to infants.

Question: Are women better at reading people’s faces and tone of voice?

Lise Eliot: Right. So the ability to read emotion in another person is a reliable difference. Quantitatively it’s in the small to moderate range so it’s about four-tenths of a standard deviation difference between men and women. Again, if a woman – if you ask a woman, "How do you feel when you describe another person’s emotion?" she will probably report a bigger response than a man will. But if you actually test people objectively, the male-female difference is smaller.

Question: Are boys hardwired more for aggression?

Lise Eliot: Yeah. Physical aggression, probably not surprisingly, is one of the more reliable sex differences. It’s about a half a standard deviation in difference and it shows up pretty early in childhood. But what’s interesting I think, and was surprising to me, is that it doesn’t suddenly change at puberty. I thought, you know, pubertal testosterone, that’s when boys really become physically aggressive. But surprisingly, no. There’s been a lot of research on this by John Archer in England. There’s no sudden change at all. So if testosterone influences aggression, and it probably does, it happens prenatally. In fact, girls who are exposed to higher levels of male hormones before birth because of a particular genetic disorder known as Congenital Adrenal Hyperplasia, these girls have been studied extensively, as you might imagine, to look at the effects of prenatal hormones.

And physical activity and aggression are definitely higher in these girls than in control girls. So there is a reliable difference in physical aggression. Although the interesting thing about physical aggression is that I have this great chart I probably should have put in the book but that boys and girls both decline very dramatically in physical aggression from the toddler years to puberty. Not surprisingly. Every two and three year old kicks and bites and scratches. And both boys and girls learn very well that they’re not supposed to do it. Boys are always do a bit more of that than girls do but they all decline as they’re trained and they learn that physical aggression is not acceptable. Now most women appreciate that there are other forms of aggression.

I think a lot of men appreciate this too when it’s not appropriate to physically aggress, there are plenty of people that aggress verbally. And girls when they hit not even puberty, even before puberty, engage in more, what’s known as relational aggression, where you – It’s sort of the best friend wars of whispering behind each other’s backs and turning friends against each other which is as prominent in girls as physical aggression is in boys. So it’s not really fair to say one sex is more aggressive than the other. One sex is more physically aggressive definitely.

Question: Is the male brain larger than the female brain?

Lise Eliot: Well, overall, if you want a reliable sex difference in the brain, the male brain is about nine percent larger than the female brain and this is true at birth and it’s true throughout life. And, you know, a lot of people want to say it’s a direct link to intelligence differences although IQ differences are – Generally there’s – Most studies find no IQ difference in men and women. But I was really interested in this. I was looking into this nine percent difference. Certainly, the difference in height is about nine percent. Men are about nine inches taller which boils down to about a nine percent difference. But I was trying to find differences in other organs, you know. Our heart, our lungs, our kidneys, and if you go into the scientific literature and you, you know, use the right search engine and you look for sex differences in the brain, you find hundreds of studies.

But if you look for sex differences in the liver, the kidneys of a human, it turns out it’s very difficult to find this data. Nobody’s interested in sex differences in these other organs. I finally was able to find some stuff on the kidney, I think, and the heart. And it’s a very similar difference, about ten to 15 percent, of larger organs in males as compared to females. And so, I don’t know. Maybe men have better hearts and kidneys and lungs than women but I don’t think so. I think it’s just that larger bodies have larger organs, period. Now when it comes to more specific differences in the brain, they’ve got to be there. You know, we know there are reliable behavioral differences and cognitive differences and even some perceptual differences. I think it’s pretty fair to say that neuroscientists have not really put their finger on what the neurobasis for these is.

There was a strong theory based on a couple of studies from the mid-'90s that claimed that when it comes to language and the fact that women are generally a little bit faster or more accurate with verbal sorts of skills, that that could be explained by the use of the two hemispheres. So there was a study from the mid-90s, very high profile, that found that women use both hemispheres for certain language tasks while men tend to use their left hemisphere which is typically the dominant language hemisphere. And I even used to lecture to my medical students on that and the first draft of the book, that was right in there.

But what I’m trying to do is not just rely on single studies but look at what we call meta-analysis which pulls all the data together and this language lateralization difference between males and females has been looked at in about 20 different studies and when you put all the data together, there’s no difference between men and women in the degree of which we use our left hemisphere or both hemispheres in language tasks. So probably because the difference in language skill is so small, you’re just not going to pick it up when you’re, you know, imaging 20 men and 20 women which most of these studies do. The one area that is looking more reliable in terms of understanding sex differences of the adult brain is emotional processing and in particular emotional memory.

A couple of different laboratories have now found stronger activation of the amygdala, in the right amygdala in men, and the left amygdala in women when they are recalling a strong emotional memory. So we’ve seen this by different labs and multiple studies, I think it’s starting to look reliable that men and women are lateralized differently in terms of amygdala activation. And that kind of fits with the verbal spatial division between men and women. If the left hemisphere’s more verbal, women tend to use their left. They may use more verbal strategies for remembering things and males may use more visual spatial strategies in the right hemisphere. So, we’re getting there with that one aspect of cognition but other things remain sort of mysterious.