Differences between sexs

[Ace Pace]

The Economist

IN THE 1970s there was a fad for giving dolls to baby boys and fire-engines to baby girls. The idea was that differences in behaviour between the sexes were solely the result of upbringing: culture turned women into ironers, knitters and chatterboxes, and men into hammerers, drillers and silent types. Switching toys would put an end to sexual sorting. Today, it is clear why it did not. When boys and girls are born, they are already different, and they favour different toys from the beginning.

That boys and girls—and men and women—are programmed by evolution to behave differently from one another is now widely accepted. Surely, no one today would think of doing what John Money, of Johns Hopkins University, did in 1967: amputating the genitalia of a boy who had suffered a botched circumcision, and advising the parents to bring him up as a girl. The experiment didn't work, and the consequences were tragic. But which of the differences between the sexes are “biological”, in the sense that they have been honed by evolution, and which are “cultural” or “environmental” and might more easily be altered by changed circumstances, is still fiercely debated.


The sensitivity of the question was shown last year by a furore at Harvard University. Larry Summers, then Harvard's president, caused a storm when he suggested that innate ability could be an important reason why there were so few women in the top positions in mathematics, engineering and the physical sciences.

Even as a proposition for discussion, this is unacceptable to some. But biological explanations of human behaviour are making a comeback as the generation of academics that feared them as a covert way of justifying eugenics, or of thwarting Marxist utopianism, is retiring. The success of neo-Darwinism has provided an intellectual underpinning for discussion about why some differences between the sexes might be innate. And new scanning techniques have enabled researchers to examine the brain's interior while it is working, showing that male and female brains do, at one level, operate differently. The results, however, do not always support past clichés about what the differences in question actually are.
Baby blues and pinks



In the past, it was assumed that a female was simply a male with hormones, says Tracey Shors, a professor of neuroscience at Rutgers University. The truth is the exact opposite. Female is the default brain setting. Until the eighth week of gestation every human fetal brain looks female. The brain, like the rest of the human body, becomes male as a result of surges of testosterone—one during gestation and one shortly after birth.



This wash of hormones creates an organ that generates typically boyish behaviour, such as rough-and-tumble play. Behavioural differences appear early. For example, a one-day-old girl will look for longer at a face than at a mechanical mobile; a boy will prefer the mobile. That it is testosterone exposure which causes such preferences is suggested by two sorts of research. Several studies have shown that girls with a genetic disorder which exposes them to abnormally high prenatal levels of testosterone often develop boyish patterns of play. As regards boys, Simon Baron-Cohen and Svetlana Lutchmaya, two researchers at Cambridge University, found that boys exposed to relatively high levels of testosterone in the womb looked less often at their mothers' faces, made eye contact less frequently and had smaller vocabularies than those exposed to lower levels—though this study has yet to be replicated successfully by other researchers.

Within a year of birth, boys and girls also prefer different toys. Boys prefer cars, trucks, balls and guns. Girls prefer dolls and tea sets. Although evolution has clearly not had the opportunity to mould a preference for tea sets, there is evidence from another species which suggests that human infants might be predisposed to prefer toys that have particular adaptive significance to their sex. Several years ago, Melissa Hines, of City University in London, and Gerianne Alexander, of Texas A&M University, gave some vervet monkeys a selection of toys, including rag dolls, pans, balls and trucks. Male monkeys spent more time with the trucks and balls. Females played for longer with the dolls.

Obviously, cultural stereotyping is an improbable explanation for this. Nor could male monkeys have evolved a preference for fire engines. The theory put forward to explain what happened—and the similar innate preferences of human children—is that the toys preferred by young females are objects that offer opportunities for expressing nurturing behaviour, something that will be useful to them later in life. Young males, whether simian or human, prefer toys that can be used actively or propelled in space, and which afford greater opportunities for rough play.
Just behave

Differences in behaviour between the sexes must, in some way, be reflections of systematic differences between the brains of males and females. Such differences certainly exist, but drawing inferences from them is not as easy as it may appear.

For a start, men's brains are about 9% larger than those of women. That used to be cited as evidence of men's supposedly greater intelligence. Actually, the difference is largely (and probably completely) explained by the fact that men are bigger than women.

In recent years, more detailed examination has refined the picture. Female brains have a higher percentage of grey matter (the manifestation, en bloc, of the central bodies of nerve cells), and thus a lower percentage of white matter (the manifestation of the long, thin filaments that connect nerve cells together), than male brains. That, plus the fact that in some regions of the female brain, nerve cells are packed more densely than in men, means that the number of nerve cells in male and female brains may be similar.



Oddly, though, the main connection between the two hemispheres of the brain, which is known as the corpus callosum and is made of white matter, is proportionately smaller in men than women. This may explain why men use only one side of the brain to process some problems for which women employ both sides.



These differences in structure and wiring do not appear to have any influence on intelligence as measured by IQ tests. It does, however, seem that the sexes carry out these tests in different ways. In one example, where men and women perform equally well in a test that asks them to work out whether nonsense words rhyme, brain scanning shows that women use areas on both the right and the left sides of the brain to accomplish the task. Men, by contrast, use only areas on the left side. There is also a correlation between mathematical reasoning and temporal-lobe activity in men—but none in women. More generally, men seem to rely more on their grey matter for their IQ, whereas women rely more on their white matter.

These examples show how tricky it is to find correlations between behaviour and differences in brain structure and brain activity. And even if a connection to brain structure is found, that does not mean it is innate. Most of these studies are done on adults, so it is not clear when differences start to arise. The brain is by no means immutable, even in adulthood. In the hippocampus, an area thought to be involved in spatial learning, new nerve cells can be born in an adult and hormones influence their birth and survival. Dr Shors says that her work has shown that the female brain, at least, is very plastic, changing dramatically during life in response to pregnancy and menopause as well as puberty.

Dr Baron-Cohen suggests that innate preferences can be carried into adulthood, too. He studies autism and Asperger's syndrome, conditions that are far more common in boys than girls. His theory is that, from birth, female brains are hardwired for understanding emotions (empathising) and male brains for understanding and building systems (systemising). Hence the diverse preferences for toys. The notion is that autistic children—and autistic adults—have extremely male brains. In other words, they are especially good at systemising and especially bad at empathising.

Autism is, indeed, an extreme example. But there are thousands of studies on psychological differences between the sexes. They have looked at personality, social behaviour, memory and abilities in particular fields. For example, men are said to be more aggressive and better at mathematics, while women are more emotional and have better verbal skills.

There are a number of problems with these studies. One, according to Dr Hines, is science's bias towards reporting positive results, so that research which shows no differences is likely to get lost. Another is that because differences between the sexes are so often popularised and played up in the popular media, people tend to pay them disproportionate attention.

For example, although it is commonly held that there are reliable differences between the verbal abilities of males and females, Dr Hines suggests this is not exactly correct. She says that the results of hundreds of tests of vocabulary and reading comprehension show there is almost no gap between the sexes. Though teenage girls are better at spelling than teenage boys, the only aspect of verbal ability that is known to show a sex difference in adults is verbal fluency (the ability to produce words rapidly). For example, when asked to list as many words as possible that start with a particular letter, women usually come up with more than men. Furthermore, even when there are differences in ability between the sexes, research suggests that the scale of these differences is often smaller than people generally believe.

[snip statistics and information]



In this study, participants played a video game in which they defended themselves from attackers, and the number of bombs they chose to drop was a measure of aggression. When participants thought they were known to the experimenter and were having their performance assessed, men dropped more bombs than women did. But when those same participants were given the impression that they were anonymous, women became the more enthusiastic bombers.

Violent or not, women have as many angry thoughts as men, if not more. In a study carried out in 2004, Robin Simon, of Florida State University, and Leda Nath, of the University of Wisconsin, found no difference between the sexes in the reported frequency of incidents of feeling angry over a period of time. However, women tended to report anger that was more intense and prolonged.

A similar result on the greater intensity of female anger was reported earlier this year by Nicole Hess, of the Max Planck Institute in Berlin, and Edward Hagen, of the same city's Humboldt University. Dr Hess and Dr Hagen, however, took the matter one stage further by asking their participants what they wanted to do about it.

The researchers read the participants, who were undergraduate students, an “aggression-evoking scenario”. They were told they had just overheard a physically smaller classmate of the same sex making false and serious attacks on their reputation to a teacher. Once again, the women were angrier than the men. The real difference between the sexes, though, was in the way they proposed to retaliate. Women usually said that they would get their own back with gossip. Men were more evenly divided, with roughly half wanting to punch the slanderous classmate.



One idea to explain this is that in animals such as humans, where there is a lot of maternal care, females find physical aggression less affordable. And just because a smear is not physical does not mean that it is less damaging than a punch. Indeed, research suggests that girls find such indirect or social aggression much more hurtful than boys do.
Does it add up?

Another behavioural difference that has borne a huge amount of scrutiny is in mathematics, particularly since Dr Summers's comments. The problem with trying to argue that the male tendency to systemise suggested by Dr Baron-Cohen might lead to greater mathematical ability is that, in fact, girls and boys are equally good at maths prior to puberty. Until recently, it was believed that males outperformed females in mathematics at all ages. Today, that picture has changed, and it appears that males and females of any age are equally good at computation and at understanding mathematical concepts. However, after their mid-teens, men are better at problem solving than women are.

Males also have better spatial abilities than females. If asked to imagine rotating a three-dimensional object, a skill useful in engineering, the difference is quite large (d=0.73 and 0.56 in different studies). In this case the limited evidence available suggests the difference is related to the post-birth testosterone surge in boys. Women who were exposed to high levels of testosterone in the womb do not do noticeably better in spatial-rotation tasks.

Men do not excel in all spatial tasks, though. Again contrary to popular myth, men and women are equally good at navigating. But this is another example of a task in which the sexes take different paths to the same destination. Women tend to rely on remembering landmarks, whereas men rely on their geometric skills to work out direction and distance.



Another proposal to explain the lack of women professors of maths and science is that even if there is little or no difference in average ability, there might be differences in the variation around this average, with more men found in the tails of the distribution curve and fewer in the middle. In other words, among males there are more idiots and more prodigies. One study of IQ, covering everyone born in Scotland in 1932, supports this idea. It showed that there were more women in the middle of the distribution, but more men at both of the extremes.



The question raised by Dr Summers does get to the heart of the matter. Over the past 50 years, women have made huge progress into academia and within it. Slowly, they have worked their way into the higher echelons of discipline after discipline. But some parts of the ivory tower have proved harder to occupy than others. The question remains, to what degree is the absence of women in science, mathematics and engineering caused by innate, immutable ability?

Innate it may well be. That does not mean it is immutable. Spatial ability is amenable to training in both sexes. And such training works. The difference between the trained and the untrained has a d value of 0.4, and one programme to teach spatial ability improved the retention rate of women in engineering courses from 47% to 77%. Biology may predispose, but even in the rugged world of metal bashing, it is not necessarily destiny.

Highlighted the most interesting sections.

[Spoonist]

The sensitivity of the question was shown last year by a furore at Harvard University. Larry Summers, then Harvard's president, caused a storm when he suggested that innate ability could be an important reason why there were so few women in the top positions in mathematics, engineering and the physical sciences.

The speech for reference...


I think that the article author quotes a lot of good research but when trying to draw his/her own conclusions makes the wrong assumptions.
The major misunderstanding being underestimating the cultural enforcement of cultural preference.
Human male children can be very physical and competetive, this is from testosterone, but how they channel this behavior is cultural. It is easily possible by the right cultural influence to give a postive channel for this and it is easily possible by the wrong cultural influence to give a negative channel for this.

[Lord Woodlouse]

The more idiots and more prodigies thing is something I've often thought myself through observation. Interesting to see it come up.

[Broomstick]

A couple of nitpicks...

The Economist

Surely, no one today would think of doing what John Money, of Johns Hopkins University, did in 1967: amputating the genitalia of a boy who had suffered a botched circumcision, and advising the parents to bring him up as a girl. The experiment didn't work, and the consequences were tragic.

Money didn't "amputate the genitalia" of the boy - that was done by the botched circumcism. An mishandled electrocautery instrument had cooked the boy's penis, it had shriveled up and fallen off. There was some surgery done for more or less cosmetic appearances, but the damage had been done before Dr. Money showed up.

To be fair -- the attempt to raise the boy as a girl was motivated, at least in part, by trying to make the best of a bad situation. At the time was believed by many that this gender switch could be made, and that it would be preferable for the kid to grow up to be a girl rather than a boy with no penis. The parents agreed to this with the best of intentions.

HOWEVER - Dr. Money engaged in some very questionable tactics along the way. The fact that the boy-into-girl had an identical twin brother made experimenting all too tempting, given the ready-made "control". And when the boy grew up into a sexually maladjusted teen the doctors in the case were more interested in covering their asses and protecting their theories than doing right by the kid. The Big Secret was revealed to the twins, the "girl" said "Oh, THAT explains a lot...!" and promptly stopped taking female hormones went elsewhere for consultation on how to reverse the damage as much as possible to make him male as possible again.

But which of the differences between the sexes are “biological”, in the sense that they have been honed by evolution, and which are “cultural” or “environmental” and might more easily be altered by changed circumstances, is still fiercely debated.

And will never be determined because the question is poorly phrased. In reality, genetics and environment play off each other.

In the past, it was assumed that a female was simply a male with hormones, says Tracey Shors, a professor of neuroscience at Rutgers University. The truth is the exact opposite. Female is the default brain setting. Until the eighth week of gestation every human fetal brain looks female. The brain, like the rest of the human body, becomes male as a result of surges of testosterone—one during gestation and one shortly after birth.

And another during puberty. Very, very important to both male pseudohermaphrodites and and hyperandrogenic women. You need the puberty surge to complete the process.

Within a year of birth, boys and girls also prefer different toys. Boys prefer cars, trucks, balls and guns. Girls prefer dolls and tea sets.

And both girls and boys will play with either type of toy spontaneously, even if not as often as with their preferred type.

Which is why you have to be very careful about these sorts of studies. At most they describes statistical averages. I played with a lot of dolls and a kid, and I still play with tea sets (being a tea addicts), but I also had cap guns, balls, cars, trucks, airplanes, and bows and arrows Come to think of it, I still "play" with cars, a pick-up truck, airplanes, and I've got a crossbow hanging on the wall of my house. Right next to some framed cross-stitch. Nor am I entirely unique - my landlord, quite the macho male, learned how to knit last year and made Christmas scarves for all his kids. While these studies may describe the behavior of large groups on average they have very little use in predicting the interests and aptitudes of individuals.

Obviously, cultural stereotyping is an improbable explanation for this. Nor could male monkeys have evolved a preference for fire engines. The theory put forward to explain what happened—and the similar innate preferences of human children—is that the toys preferred by young females are objects that offer opportunities for expressing nurturing behaviour, something that will be useful to them later in life. Young males, whether simian or human, prefer toys that can be used actively or propelled in space, and which afford greater opportunities for rough play.

Of course, one must be careful comparing monkey behavior to human - humans are very unusual in just how much care and nurturing the typical male provides towards young, and were completely unique in adopting unrelated babies to raise as our own. Humans have an enormous capacity for nurturing behavior in either gender. Culture has an enormous impact on this as well - it's not uncommon, in my experience, for male teens to be nurturing towards younger siblings when alone with them, but nasty to the younger ones if the same male teen is in a peer group of other young males and thus under peer pressure. That's a cultural response at work, not an innate one.

Likewise, female humans are quite capable of violence, even if on average they aren't so likely to indulge as the males are.

Differences in behaviour between the sexes must, in some way, be reflections of systematic differences between the brains of males and females. Such differences certainly exist, but drawing inferences from them is not as easy as it may appear.

Please underline that last sentence multiple times.

Oddly, though, the main connection between the two hemispheres of the brain, which is known as the corpus callosum and is made of white matter, is proportionately smaller in men than women. This may explain why men use only one side of the brain to process some problems for which women employ both sides.

It's also why women are more likely to recover from brain injury or stroke.

It does, however, seem that the sexes carry out these tests in different ways. In one example, where men and women perform equally well in a test that asks them to work out whether nonsense words rhyme, brain scanning shows that women use areas on both the right and the left sides of the brain to accomplish the task. Men, by contrast, use only areas on the left side.

One of the few times when separate may in fact be equal, at least in regards to end result.

The notion is that autistic children—and autistic adults—have extremely male brains. In other words, they are especially good at systemising and especially bad at empathising.

But maybe we should come up with terms less loaded than "male brain" and "female brain", because part of what gets peoples' knickers in a twist over these things is how they get mixed up with gender identification.

One idea to explain this is that in animals such as humans, where there is a lot of maternal care, females find physical aggression less affordable.

I tend to think that having more than half the population bigger and stronger than you also will tend to put the brakes on overt physical agression. I wouldn't be surprised if a study found that men 5 feet tall are more likely to engage in verbal rather than physical agression than men 6 feet tall - for similar reasons. It's stupid to take on an opponent that much bigger than you, if you can avoid it.

Males also have better spatial abilities than females. If asked to imagine rotating a three-dimensional object, a skill useful in engineering, the difference is quite large (d=0.73 and 0.56 in different studies). In this case the limited evidence available suggests the difference is related to the post-birth testosterone surge in boys. Women who were exposed to high levels of testosterone in the womb do not do noticeably better in spatial-rotation tasks.

Nonetheless, there are some women such as myself who outperform 99% of men in these tasks. Again, these statements apply to averages for large groups - they can not make predictions for individuals.

Men do not excel in all spatial tasks, though. Again contrary to popular myth, men and women are equally good at navigating. But this is another example of a task in which the sexes take different paths to the same destination. Women tend to rely on remembering landmarks, whereas men rely on their geometric skills to work out direction and distance.

This actually gets addressed in flight training. Pilots are required to show a minimum level of proficiency in both navigation modes. It's not uncommon for a flight instructor to work more on dead reckoning with women and more on pilotage (landmark navigation) with the men so their navigation abilities are evened out. Which is a demonstration of how an environmental influence (education) can either overcome or mask innate tendencies.

Innate it may well be. That does not mean it is immutable. Spatial ability is amenable to training in both sexes. And such training works. The difference between the trained and the untrained has a d value of 0.4, and one programme to teach spatial ability improved the retention rate of women in engineering courses from 47% to 77%. Biology may predispose, but even in the rugged world of metal bashing, it is not necessarily destiny.

Uh, yeah - like I said.

[Darth Wong]

Yeah, identifying the brain structure as the cause of mens' tendency to use physical aggression is unnecessary when men are simply more well-suited to physical violence. If you have a tool, you'll tend to use it.

[Mobiboros]

I thought the corpus collosum thing as debunked due to the use of a very small sample size and that a greater variance between individuals exists than between male and female brains?

[Mobiboros]

I thought the corpus collosum thing as debunked due to the use of a very small sample size and that a greater variance between individuals exists than between male and female brains?

To follow up, I found this site

http://www.indiana.edu/~pietsch/cc-sex.html

[Broomstick]

I thought the corpus collosum thing as debunked due to the use of a very small sample size and that a greater variance between individuals exists than between male and female brains?

You could probably say the same about things like "verbal skills" and "math ability".

Once again, at most these are statistical averages in very large groups.