How Different Are Boys and Girls?

image Boys are good at math. Girls are good at multi-tasking. Men talk less, and women are more empathetic. But are these differences a function of biology, or social conditioning? Do they even exist? The gap between male and female cognitive ability, as indicated by intelligence testing, has shrunk to almost nothing.

The underlying theory, presented in many books and articles across disciplines, is that the hormones that determine a baby’s sex during fetal development also cause changes in the brain.

Rebecca Jordan-Young, a Barnard professor with a doctorate in socio-medical science, decided to investigate this claim. She read 400 studies on the topic, and interviewed top researchers in neuroscience and neuropsychology. Her book, Brain Storm: The Flaws in the Science of Sex Differences is a summary of her findings. Jordan-Young recently visited Israel to speak about her book.

Sex differences and gender are  in the news. A Canadian couple is refusing to announce their baby’s sex. Naturally, the child has a unisex name (Storm) and will wear unisex clothes. They’re not the first, either—a couple in Sweden is doing the same thing.

Jordan-Young debunks the idea that men and women’s brains differ in any significant way. When she went to look at the studies, she found that they were biased from the start. For instance, definitions of masculine and feminine were subjective, and might consider playing with Legos as a sign of masculinity in girls.

Twin studies have looked at this issue, based on the assumption that the females in boy-girl twins are exposed to male hormones in utero. Some studies showed that the female of boy-girl pairs is more aggressive, but when Jordan-Young asked experts in twin studies, many reported that they had found no differences. But studies that show negative results—”file drawer studies”—are less likely to get published.  Eight published studies might show differences, but 200 unpublished studies might not.

Jordan-Young is razor-sharp and dedicated to rooting out bad science. Someone asked her about the effect of hormones like oxytocin on brain development and human personality. Women produce oxytocin during birth, lactation, and sexual activity, and it is sometimes referred to as the “mothering hormone.” Jordan-Young responded that men also produce oxytocin. As part of my lactation studies, I’ve read about its role in everyday social interactions.

Wrong assumptions about sex and gender differences affect health policy. Studies using actors show that doctors are more likely to order more tests for a male patient than for a female one, even when the two present with identical symptoms. Women, especially the elderly, get less pain medication and their symptoms are more often presumed to be psychosomatic.

Even when there are differences between the sexes, like in the risk of getting certain types of heart disease, this  may be more attributable to differences in body mass or height. The overlap means that making generalizations can lead to a wrong diagnosis.

Physically, the brains of men and women are nearly identical. The only difference is an extra nodule in the hypothalamus of women. No one is sure what it does, but comparisons with animal brains suggest it may regulate the menstrual cycle.

The theory that hormones affect brain development in utero has a serious flaw. Genitals develop as either male or female at a critical point during pregnancy. But brain development lasts longer in humans than in other vertebrates, and continues beyond pregnancy.

Jordan-Young also has noticed more sexism in child-rearing than in the past. When shopping for a toy online, she was immediately asked whether it was for a boy or girl.

So what will happen to those “genderless” children? Will their masculinity or femininity rear up in the end? Or will they be free to develop as individuals, without social gender constraints?

Update: One Tired Ema sent me this response from the mother of the “genderless baby..” Kate commented that she doesn’t go along with every one of her children’s whims.

Related Posts:

Ph.D. in Parenting wrote a post about parenting boys and girls differently.

Questions to Ask When Choosing a School for Your Children

Gender Separation in Religious Schools

Photo: mikebaird


  1. Thanks for an interesting post and made me think. I work in childcare (4 year olds) and I wonder how much is connected with how we raise the children. We have a real tomboy in our group and we’re always joking she should have been born a boy. Someone who worked with me told me how difficult it was for her to buy her 2 year old son a doll, even though she knew intellectually it was a good toy for him.

    Personally, I had no problems when my elder daughter finished playing with Barbies to pass them on to her younger brother, who also loved playing with them. And at home I think we manage pretty well not to instill gender constraints in them. But so much of it is subconscious. Would be interesting to know what happens with the Canadian and Swedish children you mentioned – including whether “hiding” their sex had any effect.

    • Glad you like it, Julie. It made me think too. One Tired Ema pointed out that the American baby has siblings, who also have to keep the secret, and that may be hard on them.

  2. Interesting but also worrying as far as health is concerned.

  3. We have boy/girl twins who are now 11. When they were little, they were like an advert for gender differences. Eg, when they were about 9 months, I was waiting to have a tyre changed. I put them on some chairs to play as the floor was dirty – our daughter sat and “talked” to me, while our son ripped the leaflet holder off the wall and threw all the leaflets on the floor. When they were a bit older, their big sisters gave them some crayons – our daughter tried out drawing, while our son tried to eat the crayons. We did not treat them any differently – when they were 2 my parents bought them both dolls for their birthday – our daughter mothered hers and our son smacked its head on the floor! However, although our son is incredibly male, he is also very good with the younger children, cooks and arranges flowers when people bring them! He has a well developed “female side”. I don’t think our daughter has a corresponding “male” side. I hadn’t heard of the twins research that way round – I have heard of the boy twin being influenced by the female hormones in utero.

    • Mrs. B. , it makes you think–wouldn’t the male and female hormones of m/f twins cancel each other out? I always understood that boys develop fine motor skills later, which could explain some behavior, but I don’t know if that is backed up by research.

  4. Great post! Very interesting topic. I worked in childcare for years and still find it tough question- Nature vs. Nurture.
    I think we also need to look at a child’s personality and how we raise them. I agree with Julie that some of it can be subconscious.
    I was a “tomboy” growing up and my 2 yr old daughter seems to be one as well. I just her take the lead…whether she’s interested in Lego, cars, dolls, whatever and let her just play. I try not to put labels on anything and just let her be a kid who is playing with toys 😉 I also have a 4 month old boy and will do the same with him.

    • Selena, when girls are “masculine” or vice versa, I think we figure that they are an exception to the rule. My two daughters are complete opposites.

  5. Studies show that teachers pay more attention to boys in school than girls.
    Great post

  6. An extra nodule in the brain? Must be the binah yeteira! 🙂

  7. When my oldest (now 8 year old) was younger, it was interesting (and a little sad) to observe how he learned from society around him what was expected of him as a boy. When he was 3 or 4, he liked pink and purple, loved arts and crafts and was a huge fan of Dora the explorer. As he grew older he learned to say that he “hates” Dora and loves blue and green.

    • A lot of the 4 year olds I work with will tell you that pink & purple are girls’ colours and that girls have long hair. If I hear that, I contradict them. If we saw a father wearing a pink shirt, I’ll remind them of that. And I remind them that my 12 year old son has long hair (most of them know him). My son is well used to strangers only noticing the length of his hair and using the feminine form to address him, until they see his face.

    • Shoshana says

      I can totally relate to the pressure – I remember my younger son, at age 3 or 4 years old, coming to pick out pajamas with me and insisting only on the pink and purple ones. So I bought them for him (though I do think I shocked my poor husband). Of course he got the message soon enough that those are girl colours… but even so, at some point in the last year, my 11yr old commented that he personally doesn’t dislike the colour pink but I must keep that a secret lest he get teased.

      I was the girl who was into sports, good at math/science, loved playing with legos, etc. Both my boys are into arts and crafts and have very strong artistic sides to them and are not into sports. And my older son has expressed an interest in recent times to consider the option to study early childhood education and open a tzaharon when he grows up. I try not to discourage it but he is well aware these are not thoughts to be expressed to his peers – but he does point out the 2 different tzharaonim in town which appear to be male run (based on their names)

      I personally believe it is more that each person is unique and its not a matter of boy girl. Maybe there are more girls who show trait Y and boys who show trait Z but its all a continuum and not all or nothing.

  8. That couple in Canada infuriate me, actually. I am the first person to dismiss useless gender-imposed rules (like girls have to have long hair, or boys can’t play with dolls, etc.) but what they are doing is not analyzing the situation and teaching their children the difference between legitimate, biology-based differences between boys and girls and archaic societal norms that deserve re-examination. They are denying a fact on that ground: a gigantic societal factor by which everyone at least somewhat defines his/her identity. They are creating an artificial environment which will not prepare their child to cope with reality.
    Boys and girls are different. Their bodies are different. There are experiences that are unique to each one that the other will never experience. But those differences are really very limited and don’t have to overtake your entire life. You don’t have to erase gender to teach your daughter she’s allowed to devote her life to her career or to teach your son he’s allowed to devote his life to raising his children.
    They got the attention they were seeking… now hopefully they’ll take a pill and stop screwing around with their kids like they are lab mice.

  9. The couple in Canada is not concerned that their kid develop a particular sexual identity. They think it doesn’t matter for adults either, when the kid grows up it can decide what it wants to be.

    That is different to gender stereotypes that make it harder for a boy to eventually be an adult male and for a girl to eventually be an adult female, like telling boys not to express emotion and telling girls not to be too smart or to put themselves forward.

    I also think the stereotyping is worse in America than in Israel. Here in Israel men cry at a loss, care for children, cook. Both girls and boys are told (not asked, as I originally thought,) “What will you do when you get to the army?” which means life is tough so don’t be too soft. So in spite of the boys playing soccer and the girls wearing plastic jewelery they both can play with dolls and they can both say “No!”


  10. JoabStories says

    I agree with Lauren – there are differences and denying them will not benefit anyone.
    In “Keeping the Love You Find” Hendrix quotes studies that claim that women’s brains have a thicker corpus callosum – a cable connecting the right and left hemispheres- which means women can integrate the two hemispheres better. Although, perhaps such differences are also nurtured and are not natural – that would be hard to tell.
    In any case, from a Jungian point of view the unconscious is always experienced as female and consciousness as male, in every culture throughout history. Gender seems to be an important part of the development of consciousness, so I don’t see it disappearing in the near future, no matter how hard some people’s try to deny the fact.

    • To reiterate, Jordan-Young said there are no physical differences except what I mentioned. She also said there are many popular books on the market that “make things up,” especially bestsellers “Male Brain,” and “Female Brain,” despite the author’s good credentials.

  11. Using MRI and other recent methods there seems to be a lot of evidence of such a physical difference. I don’t see why or how such imaging studies would be biased – it’s just taking images, measuring, and correlating with gender – pretty straightforward.
    Of course, behavioral studies are another thing- operational definitions of human behavior and feelings are notoriously slippery and prone to bias, even in more neutral subjects, so I’m sure that Jordan-Young found a lot of bias in behavioral gender studies.
    Anyway, if anyone is interested, here is the wikipedia link with several references:

    • If Wikipedia can be believed, the jury is still out on this one. Also, the question is whether these differences, if they exist, are indeed sex related. In other words, can you look at the corpus callosum of an individual and determine whether an individual is a male or female. Even discounting all the studies listed that showed no difference, it seems the answer is no. And it may be related to physical differences like height or weight.

  12. While I don’t doubt that environment plays a large part in developing certain gender differences (like profession, recreation preferences, favorite color, etc.), I’m not sure that the fundamental difference between men and women can be found in something as simple as the physical structure of the brain or secretion of a hormone. To me, it’s like proving that we have a soul. It’s there, but where is it? I think gender differences is in that same esoteric field.

    Like Shoshana said, it’s a continuum. Some girls will be more on the “boy” side, and vice versa. But there are still “sides,” and like JoabStories said, I don’t think those are going to go away any time soon.

    That said, I think it’s entirely possible to raise our children to maximize whatever their potential is, regardless of society’s stereotypes. However, to go so far out of the box (as I believe the Canadian couple is doing) hinders our children’s ability to function within the current society, flawed as it may be, and that is not good parenting.

  13. sylvia_rachel says

    I read about Storm recently (that family is local), and I’m conflicted. On the one hand, what an interesting and potentially liberating idea, to raise your child without rigid expectations based on his/her sex. On the other hand, to ask a 5-year-old and a 2-year-old to keep that secret, and expect them to never slip up? And for such a drastic social experiment shouldn’t one have informed consent from the participant? I don’t know.

    But wow, do people ever have hangups. When I was pregnant with DD, we were constantly asked “Are you having a boy or a girl?” We didn’t know, and didn’t want to know, until she was born. We wanted to be surprised, and it didn’t seem to us that we needed to know to prepare for a new baby — new babies don’t care what colour their little suits are, or how the nursery is decorated (not that we had one), or whatever. You wouldn’t believe how much flak we got from some people over that. o_O

    I find the increased gendering of toys (not to mention poor innocent colours) extremely irritating. It’s got to the point where you almost can’t find anything that’s unequivocally gender neutral. Why is it necessary, for instance, to sell Mega Bloks (giant legos, basically) in black, blue, red, and yellow for boys and in pink, purple, and turquoise for girls? I remember once when DD picked out a pair of shoes she really liked (she was about two, I think) and the sales person was reluctant to let her try them on because they were boys’ shoes. She tried them on, they fit, she loved them. (She wore them with her favourite outfit: black turtleneck, black yoga pants, and black socks.) In a lot of stores that sell kids’ clothes, it’s incredibly hard to find a piece of girls’ clothing that isn’t pink or purple. What if your daughter doesn’t like pink and purple? Or what if your son likes pink and purple, but doesn’t like frilly things?

    So I have a certain amount of sympathy with those parents. But I definitely wouldn’t do the same thing myself.

    • I also found a lot of people couldn’t understand why I didn’t know the sex of both my babies (I think it’s a much more common thing here in Israel than England). I didn’t want a pink bedroom for my child and blue is good for boys and girls. I did get encouragement from a few older women who didn’t have the choice of knowing with their babies.

      I remember going to buy our 2 year old daughter sandals. I was looking for practicality rather than a good colour. My husband and I split up in the shop and he showed my daughter one pair to try on. Another shopper (a woman) told him they weren’t good as they were for boys.

    • Observer says

      Let me put it this way. All of your points are valid, especially the issue of “gendering” toys. But, I don’t think that has ANYTHING to do with what these parents are doing.What they are doing to the baby is bad enough, but what they are doing to the older two children is even worse. On top of everything else, has anyone thought about the effects on their use of normal language created by referring to the baby as “it”? In English only inanimate objects are referred to as “it”, NOT people. Best case, they are likely to offend a lot of people and make a lot of others see them as very odd, and not “charmingly” so.

  14. Rachel Q says

    I now try not to impose gender biased on my kids… the end result is that my son is surrounded by girly things 🙂
    Our first child is a girl so we got (brought or received) many dolls and other girly toys. I also made sure she had plenty of educational toys, legos, kaplas, etc. When my son was born i dressed him in pink pijamas since I refused to buy new ones. He wears a pink helmet, since I think it’s a waste of money to buy a new one. etc. I know buy a lot more gender neutral things:)
    He takes the dollies for a ride on his sister’s pink stroller, cooks, puts stuffed animals to sleep, wears a pink mitpachat like his big sister, etc.
    I see that at around 3-4 the stereotypes are so strong in gan that he will quickly learn and behave more like a stereotypical boy (for good or for bad).
    I guess I’m ok with some differences, since biologically we are different. Most men are physically stronger and can’t get pregnant or nurse. But beyond the physical difference I don’t like many of the other ones, like the math myth. What get’s me really angry is the “boys will be boys” idea. I see many people who allow boys to misbehave (hit for example) and simply say they can’t possibly discipline the kids since boys will be boys. I’ve had many arguments with other moms who simply assume their boys have to be wilder than the girl, so they tolerate that type of behavior, thereby reinforcing the wild behavior as acceptable.

    • Observer says

      Oy! It may very well be true that boys are more likely to be more wild than girls. That doesn’t mean that they can’t be taught at a very, very young age that certain behavior is simply unacceptable. Yes, even a 4-5 year child, boy or girl, can learn that it is NOT ok to hit! In my opinion a “Boys will be boys” response to hitting is simply a cop out.

  15. Peggy Orenstein referenced the couple in Sweden in her book Cinderella Ate My Daughter. (my comments on it are at She also recalled the story of child X who was raised without gender, a rather optimistic story from the 70s that she doesn’t quite believe could work in the real world. I’m the mom of very ungirly girls who generally despise pink. When it came to pick out her sports themed lunch box, my youngest skipped the pink soccer ball and would only consider the plain baseball or basketball versions. However, the girls do have a very gendered curriculum; “tznius” is the topic of a whole course in high school. My son has never been the rough and tumble type boy, though he’s been on an all-learning all the time quick for nearly 4 years now.