While it's now (almost) generally accepted that men and women are at most only very slightly different in average IQ, there are still a couple of lines of evidence in favor of a gender difference.
First, there's the idea that men are more variable in their intelligence, so there are more very smart men, and also more very stupid ones. This averages out so the mean is the same.
Second, there's the theory that men are on average better at some things, notably "spatial" stuff involving the ability to mentally process shapes, patterns and images, while women are better at social, emotional and perhaps verbal tasks. Again, this averages out overall.
According to proponents, these differences explain why men continue to dominate the upper echelons of things like mathematics, physics, and chess. These all tap spatial processing and since men are more variable, there'll be more extremely high achievers - Nobel Prizes, grandmasters. (There are also presumably more men who are rubbish at these things, but we don't notice them.)
The male spatial advantage has been reported in many parts of the world, but is it "innate", something to do with the male brain? A new PNAS study says - probably not, it's to do with culture. But I'm not convinced.
The authors went to India and studied two tribes, the Khasi and the Karbi. Both live right next to other in the hills of Northeastern India and genetically, they're closely related. Culturally though, the Karbi are patrilineal - property and status is passed down from father to son, with women owning no land of their own. The Khasi are matrilineal, with men forbidden to own land. Moreover, Khasi women also get just as much education as the men, while Karbi ones get much less.
The authors took about 1200 people from 8 villages - 4 per culture - and got them to do a jigsaw puzzle. The quicker you do it, the better your spatial ability. Here were the results. I added the gender-stereotypical colours.
In the patrilineal group, women did substantially worse on average (remember that more time means worse). In the matrilineal society, they performed as well as men. Well, a tiny bit worse, but it wasn't significant. Differences in education explained some of the effect, but only a small part of it.
OK.
This was a large study, and the results are statistically very strong. However, there's a curious result that the authors don't discuss in the paper - the matrilineal group just did much better overall. Looking at the men, they were 10 seconds faster in the matrilineal culture. That's nearly as big as the gender difference in the patrilineal group (15 seconds)!
The individual variability was also much higher in the patrilineal society, for both genders.
Now, maybe, this is a real effect. Maybe being in a patrilineal society makes everyone less spatially aware, not just women; that seems a bit of a stretch, though.
There's also the problem that this study essentially only has two datapoints. One society is matrilineal and has low gender difference in visuospatial processing. One is patrilineal and has a high difference. But that's just not enough data to conclude that there's a correlation between the two things, let alone a causal relationship; you would need to study lots of societies to do that.
Personally, I have no idea what drives the difference, but this study is a reminder of how difficult the question is.
Hoffman M, Gneezy U, List JA (2011). Nurture affects gender differences in spatial abilities. Proceedings of the National Academy of Sciences of the United States of America PMID: 21876159
27 comments:
The higher variability in the patrilineal group compared to the matrilineal group may be because of the difference in sample size: 468 vs 811 respectively.
Good point.
Matt: that's almost certainly the case, as most common estimates of variance (sem, std, var, etc.) decrease as a function of sample size.
Neuroskeptic: I've not read the paper, but did they really not report the results of an ANOVA? That's seems like the bare-minimum statistical analysis they should conduct in a 2*2 design like this. You've got society and gender as your factors, and it looks like there might be a main effect of society (which you're suggesting here), and an interaction between society and gender, but probably not a main effect of gender.
Now off to read the paper...
They reported it, but didn't cover it in the Discussion.
Ahhh, ok. Gotcha. Still very odd and, as you said, probably kinda important?
I really think what keeps women out of the highest academic levels in the hard sciences is that you have to give up everything except your career, often including kids.
Growing up, I remember all the studies that showed girls were not as good at math as boys, and people saying it is innate. . . then those gaps disappeared. Now, people altered the message and say that women are on average not as good at higher math, and it is innate. I think it's all cultural, and the other difference, which may also be cultural, is that fewer women are willing to give up everything else, including family, to doggedly pursue one interest. Now, I happen to think that is cultural too, because look how much more fathers do at home with their kids nowadays (on average).
hmm, interresting. but... let's think about it this way: say, men have no better inborn spatial skills per se but have only higher genetic predispositions to develop them, if needed. in cultures where men are not allowed to become owners & "leaders" they probably are much less forced to improve skills as their responsibility is lower. and there probbly is less man-to-man competition, too. as a result, skills may remain undeveloped and predisposition hidden. of course... there could be the same cult. hidden predispositions for women, as well as there could be no predisposition at all. did they discuss smthg similar?
The important point is that the performance gap varied at all. If it's about gender, per se, then it shouldn't. If it's only about gender because that covaries with something else (eg status) then it will. Given the extreme claims about these gender gaps, showing you can push it around essentially as a function of expectations of how well you can do things is important.
If you want a broader context for these types of results, Cordelia Fine's excellent Delusions of Gender is the place to look.
(A side note: they don't actually seem to have run the obvious ANOVA on those data; I couldn't see any report of all the main effect and interaction terms in the paper or Supplementary Text).
"The important point is that the performance gap varied at all. If it's about gender, per se, then it shouldn't."
in neuro`s article it is interpreted as innate vs. culture. and to me it is pretty the same if there is innate trait or there is "just" innate genetic predisposition (some kind of inborn advantage). couse quality of skills then, though acquired throughout life in response to cultural enviroment is still limited to some inborn predeterminants. and if men vs women are exposed to the same level of stimulation, results would be strongly gender/sex dependent. btw, it`s a bit similar to muscle strenght. you probably can find group of people where there is no significant (or strong) gender/sex difference in hand-griping or squats with load but this does not automatically mean that in general (in average, median) men are not "innate stronger" then women. or does?
Based on another article I had read about this study, I had wondered why, if in one the men were primary and in the other the women were primary (they were painted as opposites of each other), the results for the Khasi didn't show the opposite of that of the Karbi rather than having no significant difference between man and women. However, in your post, you mention:
"...Khasi women also get just as much education as the men, while Karbi ones get much less."
I think that is one of the important factors if one were to use this to champion access to education. But, then it is also important to point out the fact that in Western countries in which women have more access to education and are much better at maths (Sweden, being the typical example), this sort of effect with spatial skills is not found.
Well, there's already a lot of questions about this idea that men have better spatial intelligence than women. To the best of my knowledge, there is absolutely no evidence of any anatomical or physiological difference between men and women that could explain such an effect. Moreover, this claim that "men are just more variable than women" on certain tasks is not a statement which tells us little about "innate" differences between men and women. In fact, it is a completely non-informative statement about these groups of individuals, except to say that we have noticed a trend in some particular outcome measure where men perform in a more variable fashion than women. Why should "innate" differences produce an effect on this outcome, while environmental factors have little effect? This line of reasoning is pure silliness. And to say that we have "controlled" for all environmental differences is self-evidently false.
And I suspect the real reason why this argument has been used is to provide a "biological" explanation for why men seem to dominate high income jobs--those which require the skills which men are supposedly better at--while women are still disproportionately relegated to lower paying positions. In contrast, I think it is easily a more parsimonious explanation to propose that the differences in income seem between men and women represent a systematic bias in how our society views males and females, which leads us to encourage young men towards stereotypically male professions, which also (unsurprisingly) happen to be the most highly rewarded professions.
Also, I realize the following is anecdotal, but my understanding is that it is relatively representative of the sorts of biases we have in society. As I recall from my time in high school, which was only within the last 10 years, there was a significant bias in all of my math and physics classes towards a sort of "boys club", where it was implicitly, and sometimes explicitly, assumed that the real competition was amongst the men, whereas young women were really just along for the ride. Even when they got better marks. From what I've heard, this kind of stereotype is still pervasive in "male-dominated" areas such as engineering, physics and mathematics.
As far as I am concerned, the null hypothesis remains that there are no underlying differences in how male and female brains are "designed" which affect spatial reasoning. Until legitimate evidence is provided to suggest such a difference, it seems bizarre to even consider this belief, particularly in light of the apparent and systematic differences in how we raise and educate males and females in this society.
There have been a couple of Canadian studies (that I have seen but didn't record citations for at the time and have not managed to locate since) that looked at various spatial task performance as a function of women's monthly cycle. They found that spatial performance was low at peak fertility while it approximated men two weeks later. I haven't seen the study replicated, but the experimental design is interesting, and has been conducted in a variety of other contexts.
If it were replicated, it would have some important pedagogical consequences for STEM instructors. Specifically, while men may be indifferent to a spatial subject curriculum where sequential topics are relentlessly taught one after another, women might do better with a format in which the spatial subject curriculum revisits new lessons a couple of weeks later with an in depth review. In general, that women might benefit from more of an integrated math and science curriculum that hits the same subject multiple times in an educational career, rather than a linear one that hits each subject once in depth before going onto the next. Given the rather brutal and linear way that first year students in physics and engineering are expected to absorb both calculus and calculus based physics in the first year of college, with high flunk rates for those who attempt to learn the subject in that canonical matter (chemistry has similar attrition) as opposed to mastering it before starting college, it isn't implausible to think that a pedagodgy that favors men (even completely without an discriminatory intent) could have a major impact on gender makeup of those fields that is largely a product of teach methods.
The existence of a performance difference on spatial tasks in Western societies has been frequently replicated by multiple methods, so the question is not so much whether there is a difference, but why there is a difference. This study doesn't have the depth or robustness of the many other studies conducted by other methods with other populations. For example, to the extent that there are genetic components of spatial ability, the founders effects on population performance in the most recent study are likely to dwarf universal gender considerations.
Now, I recall encountering studies that suggest that women are on average actually better at certain sorts of spacial tasks -- specifically, recalling the location of objects in 3D arrays of things.
Something as crude as "spatial processing" is probably too crude.
As you stated, " But that's just not enough data to conclude that there's a correlation between the two things, let alone a causal relationship; you would need to study lots of societies to do that." More studies have to be done and data gathered towards this kind of research. The initial findings are astonishing.
I am writing a lit survey re: spatial ability sexual dimorphism. You might be interested to read these papers-
The Hunter-Gatherer Theory of Sex Differences in Spatial
Abilities: Data from 40 Countries. Irwin Silverman, Jean Choi, Michael Peters (2007)
In 40 of 40 countries and in all 7 ethnics groups studied, males had significant advantage in spatial ability.
Silverman et al (1996) compared Japanese and Canadians ("Homogeneity of Effect Sizes for Sex across Spatial Tests
and Cultures: Implications for Hormonal Theories") and Mann et al (1990) looked at Japanese vs US students ("Sex Differences in Cognitive Abilities: A Cross-Cultural Perspective"). Both studies found male advantage in the nations studied.
In 1993 Owen & Lynn studied blacks, Indians, and whites in South Africa ("Sex Differences in Primary Cognitive Abilities Among Blacks, Indians, and Whites in South Africa") also finding a superior male performance bias in each of those cultures.
Whatever the effect of culture, it seems to similarly impact males and females simultaneously.
Trot out all those studies that women are not as good (on average) in spatial intelligence. I still don't believe the difference is innate. 30 years ago, men trotted out all those studies that said women were not as good at math in general, which that difference is now gone, in places where girls have equal access to education. The people pushing that information were just as convinced they were right.
I don't understand the point of this research anyway, because there is so much overlap in ability between men and women, the information is useless when applied to an individual.
Anonymous, be as skeptical as you like. Just be aware that the evidence here comes from hundreds of studies done over 5 decades covering many cultures, including the most socially advanced democracies.
Consider, too, that math and spatial ability are different. Math is a skill which can only be imparted by education. Navigation, conversely, is something almost all animals have to do as part of their lives. It isn't taught at all.
Some biological basis is well established. Even in humans, if you augment their androgens, you see variance in their spatial ability performance. In rats, males are better navigators- unless you remove their testes at birth- then they perform just like females.
Linn Peterson did a literature survey, specifically looking for age effects on spatial ability sexual dimorphism. In other words, she was looking for a time when the male bias "appears" but she didn't find one. The male advantage remains, even in children. Here you'd have to argue that (American) boys are educated and girls are not, even while their grades are about the same.
I'm curious if you'd argue that aspects of cognition where females are superior are also "mistakes" yet to be over-turned. For example, females consistently and significantly outperform males in spatial memory and object location; they also do better in verbal fluency. Are these also illusory?
The point of my research is not to say what sex is better at anything; it is to try to understand why there are differences, and ultimately how those faculties originally came about.
Hi!
Sorry that the following comment has nothing to do with the issue at hand but I was wondering whether you could review the following two articles on anti-depressants and "tardive dysphoria":
1)Andrews et al. "Blue again: perturbational effects of antidepressants suggest monoaminergic homeostasis in major depression" - http://www.frontiersin.org/evolutionary_psychology/10.3389/fpsyg.2011.00159/abstract
2)El-Mallakh et al. "Tardive dysphoria: The role of long term antidepressant use in-inducing chronic depression" - doi:10.1016/j.mehy.2011.01.020
Thanks.
All the best,
Gittele
@Edward Clint
Most of these studies are flawed in that they are testing populations which are treated differently from birth. To say that there is cross-cultural evidence that either sex performs better at a given task could just as easily be explained by cross-cultural expectations about gender norms as it could by so-called "innate" differences in ability.
I think it goes without saying that sex-differences in hormone expression are the only really plausible "biological" explanation for this phenomenon.
Along these lines, the argument could be made that sex differences in hormone expression might affect a variety of abilities such that males and females on average have sex-specific talents. However, I agree with a previous commenter that the functional differences between these groups is unlikely to be all that significant, given that variation within each human sex on most traits tends to be greater than variation between each sex. Moreover, I would make a stronger argument than that, which is to say that there is little physiological basis for claims such as "androgen expression improves spatial intelligence".
You appear to quote findings which refute this from a behavioural perspective. Can you cite them? It seems to me that there are some obvious concerns with these sorts of studies. For example, removal of a male rat's testees will not only affect its hormone expression, but also as a direct result, its behaviour. This makes it perfectly plausible that behavioural performance declines in neutered rats due to a decrease in the amount of practice that these rats have on navigation tasks. I really cannot comment on the human study without more information about what "spatial ability" was measured.
Hence, I think that it is infinitely more plausible that differences in abilities such as "spatial intelligence" between human males and females reflect behavioural differences driven partly by cultural realities and partly by hormonal expression. Of course, the important point to consider with respect to this argument is that it is unlikely that high levels of estrogens would specifically affect female behaviour such as to reduce the number of women interested in engineering or physics. This seems implausible. What this suggests to me is that the differences we see on most measures of these fairly abstract abilities are due primarily to cultural norms, rather than such "innate" differences between groups.
Gittele: thanks. I am planning to cover the first one paper when I get back from holiday in a week.
Hello Neuroskeptic
This is off topic but I am hoping that you have somethng to say about this.
Would you possibly point out examples of fMRI studies that have provided new understanding of how the brain works? I would really like to know what new understanding has come from fMRI rather than corroboration of the old.
Thanks to Edward Clint for introducing a bit of actual science into this touchy feely conversation.
In the modern politically correct world, actual science is not allowed, however. So we must make do with contrived quasi-scientific studies of Indian tribes so far distant as to be inaccessible to virtually all modern science.
Yes, it is all cultural, environmental, and behavioral, my dear. Now can we please go to bed?!
Nobody has commented on the inordinate time it took EVERYBODY to complete this simple jigsaw. Come on! Over 35 seconds for every group to solve a 4-piece jigsaw? The average 10 year old in London could do it in less than 15 seconds. I think we are looking at a cultural confound here.
We would the researchers assume that these people were motivated to solve the puzzle quickly? I don't think the monetary incentive assured that they would be motivated. The times that it took to do this 4 piece "puzzle" don't appear to indicate significant motivation. These times look like those of disinierested participants.
They took more time, because it's not habitual to solve puzzle where they live?
I have been in China and apparently they block blogs there... I respond to a few criticisms below.
"However, there's a curious result that the authors don't discuss in the paper - the matrilineal group just did much better overall."
We did report the main effect of society in the paper. That society can influence spatial abilities has been well established (see my reference 15). What is unique about our study is that we are the first to demonstrate that society can influence gender differences as well.
"There's also the problem that this study essentially only has two datapoints."
If one wants to conclude that culture influences gender gap in spatial abilities it is not enough to pick two societies and measure the gender gap in spatial abilities within each because the two societies may differ not just on culture but also on, say genetics or climate. One way to get around this issue is to study many societies. If culture is independent of other factors then with sufficient many societies one can analyze the effect of culture and hope that other effects "wash out." This is the justification for having "large n." However, if other factors covary with culture, e.g certain cultures are more likely to occur when a population has genes coding for more testosterone receptors or arid climates, increasing the number of societies studied will not solve this problem.
An alternative method is to compare two societies that are matched on everything but culture. This is precisely what we did, since the Khasi and Karbi have the same means of subsistence, are geographically interspersed, and are genetically close kin. We can be certain that our result is due to cultural differences; we don't need to rely on the law of large numbers to rule out the effect of other differences because there aren't really other differences to rule out. But our study has the added benefit of not having to rely on the (implausible) assumption that culture doesn't covary with other variables, like genes and climate.
"let alone a causal relationship"
Of course correlation does not imply causation. Which is why there is the experimental method.
Imagine that we ran the following experiment: we took 1,279 villagers from the same gene pool and the same geographic location and randomly assigned half of them to be raised in a patrilineal society and half of them to be raised in a matrilineal society, and we later measured their spatial abilities and found a gender gap in the first group but not the second group. We would then, rightly, conclude that nurture affects gender differences in spatial abilities. Would this address the causation issue? Certainly; that is the logic behind the experimental method.
We of course, did not randomly assign individuals to society; “nature” did this for us long before we arrived. Hence scientists refer to this design as a “natural experiment.” The logic is nevertheless the same as with a true experiment; so long as we are confident that nature did her assigning randomly, e.g. nature didn’t assign women with better spatial abilities to be born into the matrilineal society, we can still infer that nurture affects gender differences in spatial abilities.
-Moshe
Thanks for the interesting comment; I'll reply next week when back from holiday.
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