Glass Ceilings and Testosterone:
The Debate on Sex Differences in Spatial Skills
We've all heard about it. Glance casually at a lecture hall of engineering students and you have to squint to find the few women sprinkled in the midst of a sea of men. Pass a table of girls studying at a library and hear a conversation about economics, minority rights, child psychology, or Buddhism, but seldom physical chemistry. In the U.S., women make up only 19% of the science, engineering, and technology workforce; in academia, only 8.3% of tenure-track math professors.
Why do so many girls shy away from math and science? Tasked with answering this question, evolutionary psychologists in the second half of the 20th century turned to the hunter-gatherer society of our evolutionary ancestors for an answer. In his book Why Men Won't Ask for Directions: The Seductions of Sociobiology, sociobiologist Richard C. Francis wrote, "Because Fred and Barney did the hunting, they had to range much farther than their mates, whose own duties revolved around camp life: watching the kids, gathering foodstuffs in the vicinity, and so on. As a result, the males experienced stronger selection for spatial cognition than did the females."
Evolutionary Adaptation
Alright, the question is answered, right? Men are just smarter than women because they hunted while women stayed behind to take care of camp. Well... hold on. There are a few problems with this."A lot of people who argue for major cognitive sex differences in humans argue as though sexual division in labor, which is at most 100,000 years old, is what drove the major differences," said Dr. Kathryn Clancy, a professor of anthropology at the University of Illinois at Urbana-Champaign who studies evolutionary endocrinology. "For something as major as cognitive sex differences, I would expect a lot more evolutionary time to elapse than 100,000 years."
London School of Economics evolutionary psychologist Satoshi Kanazawa added, "Men and women within a population have always faced the same level of evolutionary novelty throughout evolutionary history, because they have always migrated together." This means that we men aren't more or less "evolved" than women.
Another problem with this hunter-gatherer hypothesis lies in simple genetics. If, indeed, the males who could form better cognitive maps of their hunting terrain brought home more impala and were considered sexier than their less-successful companions, their alleles (gene variants) wouldn't just be passed onto their sons. Their daughters would inherit them too! Smarter hunters would mean smarter sons and daughters, which would keep cognitive maps in both sexes roughly equal.
"A hypothesis can sound great but that doesn't mean it can be tested," said Dr. Charles Whitfield, professor of genetics at the University of Illinois at Urbana-Champaign. "Very often you have 'Just So' hypotheses, where you tell a story to try to explain something. These are very hard, if not impossible, to test."
Another problem with this hunter-gatherer hypothesis lies in simple genetics. If, indeed, the males who could form better cognitive maps of their hunting terrain brought home more impala and were considered sexier than their less-successful companions, their alleles (gene variants) wouldn't just be passed onto their sons. Their daughters would inherit them too! Smarter hunters would mean smarter sons and daughters, which would keep cognitive maps in both sexes roughly equal.
"A hypothesis can sound great but that doesn't mean it can be tested," said Dr. Charles Whitfield, professor of genetics at the University of Illinois at Urbana-Champaign. "Very often you have 'Just So' hypotheses, where you tell a story to try to explain something. These are very hard, if not impossible, to test."
Testosterone
So, it looks like the "evolutionary" argument doesn't hold much water. Another hypothesis that has been proposed is that the hormone testosterone could be pushing a separation between the sexes regarding spatial ability, which in turn causes the huge gender gap we're seeing in science and technology.
"Solid evidence has established that males display superior performance relative to females on tasks pertinent to way-finding in humans and many animals," wrote Edward Clint and colleagues at the University of Illinois in a 2012 study on the adaptive value of spatial ability in animals in The Quarterly Review of Biology. "The superior performance in males has been documented across cultures and across species, and appears to be related to the hormone testosterone."
"Note that, if true," the authors added, "a male advantage in one arena of cognition does not imply superior cognition in other areas. Indeed, it has been found that females outperform males on other tasks, such as object memory location, verbal fluency, and recognition of facial emotional expression."
If testosterone is the culprit, then, differences in spatial cognition could have formed as a side effect similar to male patterned baldness or acne. The trait itself doesn't have an adaptive benefit; rather, it got pulled alongside something that did.
The experiments linking testosterone and spatial cognition in humans go as such: men and women are presented with pictures of 3D Tetris-like shapes and then asked which pictures are the same block rotated into different positions. A more elaborate study was conducted in 2000 by Dr. Irwin Silverman, of the University of York, Canada, which involved leading people into unfamiliar parts of a wooded area and asking them to point towards their starting location. In both of these types of experiments, men outperform women.
"Solid evidence has established that males display superior performance relative to females on tasks pertinent to way-finding in humans and many animals," wrote Edward Clint and colleagues at the University of Illinois in a 2012 study on the adaptive value of spatial ability in animals in The Quarterly Review of Biology. "The superior performance in males has been documented across cultures and across species, and appears to be related to the hormone testosterone."
"Note that, if true," the authors added, "a male advantage in one arena of cognition does not imply superior cognition in other areas. Indeed, it has been found that females outperform males on other tasks, such as object memory location, verbal fluency, and recognition of facial emotional expression."
If testosterone is the culprit, then, differences in spatial cognition could have formed as a side effect similar to male patterned baldness or acne. The trait itself doesn't have an adaptive benefit; rather, it got pulled alongside something that did.
The experiments linking testosterone and spatial cognition in humans go as such: men and women are presented with pictures of 3D Tetris-like shapes and then asked which pictures are the same block rotated into different positions. A more elaborate study was conducted in 2000 by Dr. Irwin Silverman, of the University of York, Canada, which involved leading people into unfamiliar parts of a wooded area and asking them to point towards their starting location. In both of these types of experiments, men outperform women.
Gender Roles and Societal Expectations
While testosterone is linked with greater spatial knowledge, we still have the confounding variable of societal expectations that few studies have been able to address. Societies promoting gender equality, such as Sweden and Norway, still have these gender differences in spatial abilities. Could the true issue lie deeper?
A 2011 PNAS study by Dr. Moshe Hoffman and colleagues found startling differences between two genetically- and geographically-similar tribes in northeast India, the Karbi and the Khasi. The Karbi, a patrilineal tribe where women can't own land and the oldest song inherits all property, had the expected male-superior results on a visual puzzle. However, the Khasi, a matrilineal tribe where daughters inherit land and men are expected to hand over their earnings to their wives or sisters, had no gender gap at all. Women in the matrilineal tribe were equal to the men on the test, despite much genetic similarity to the patrilineal tribe.
"Don't forget that there's a U-shaped curve for testosterone and spatial skills in men: too much is as bad as too little," said Dr. Virginia Valian, co-director of the Gender Equity Project and professor of psychology at Hunter College - CUNY. "People can learn to become more or less skillful at spatial manipulations. The Khasi tribe's data show one sort of effect."
Dr. Davis Tzuriel and doctoral student Gila Egozi of Bar-Ilan University, Isreal, have shown that girls can be taught to change their strategies with 3D block figure analyses. Though the process is time-consuming, teaching girls to use analytic rather than holistic analysis eliminates the gender in these spatial tests.
"What is most important here is understanding what goes into the skill. It's not as if people have it or they don't," said Valian. "We can distinguish between different types of strategies (analytic vs. holistic) and it turns out that one is superior. Then we can ask why males tend to use one type and females another type."
In Valian's book Why So Slow? Advancement of Women, she uses the term "glass ceiling" to describe the lack of women in leadership roles of organizations. It implies that invisible influences, rather than overt discrimination, keep women from ascending. It also implies that these influences are unlikely to disappear soon and that female job performance is at least equal to their male peers'.
"Subtle sexism is cumulative," said Clancy. "A lot of people like to describe these narratives of 'It used to be bad, but not anymore,' but I still see these problems every day. I was a little girl when they made the Barbie that said 'Math is Hard.' But my daughter was just born and last year, JC Penney released the 'I'm Too Pretty for my Math Homework' t-shirts."
Where from Here?
Gender differences in spatial skills clearly compose a complex, highly-charged debate that is unlikely to be resolved any time soon. Testosterone is correlated with spatial skills, but perhaps we're approaching the issue incorrectly. Women perform more poorly than men on spatial tests, but how much is due to a lifetime of being discreetly told they're not as smart at math as men?
"Science is not just about math ability," said Clancy. "You need creativity, intuition, motivation. You can't get defensive. You're constantly modifying what you do. This is not something you can test with the ways we're using to tell children what they should be. A mathematician doesn't do arithmetic."
Valian said, "To both male and female students: treat each other seriously and have high expectations for each other, not just in math and science but across the board. It means stepping up to the plate and being willing to fail in order to learn, and being willing to let others step up to the plate."
Further Reading
Francis, RC. 2005. Why men won't ask for directions: the seductions of sociobiology.
Princeton University Press.
Hoffman M, Gneezi U and List, JA. 2011. Nurture affects gender differences in spatial
abilities. Proceedings of the National Academy of Sciences. 108:
10.1073/pnas.1115576108
Silverman I, Choi J, Mackewn A, Fisher M, Moro J and Olshansky E. 2000. Evolved
mechanisms underlying wayfinding: further studies on the hunter-gatherer theory of
spatial sex differences. Evolution and Human Behavior. 21: 201-13.
Valian V. 1999. Why so slow? Advancement of Women. MIT Press.
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