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Sheryl Sorby, a professor of engineering education at Ohio State University, was used to getting A’s. For as long as she could remember, she found academics a breeze. She excelled in math and science in particular, but “I never thought there was a subject I couldn’t do,” she says matter-of-factly.

So when she started engineering school, she was surprised to struggle in a course most of her counterparts considered easy: Engineering graphics. It’s a first-year course that sounds a bit like a glorified drawing class to a non-engineer.

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The hardest part is orthogonal projection, a fundamental engineering task. Given a top, front, and side view of an object, engineers must be able to mentally synthesize two-dimensional representations into a three-dimensional object. It’s easy—if you’re good at what psychologists call mental rotation.

Sorby wasn’t. To her surprise and confusion, she found herself overwhelmed. “It was the first time I wasn’t able to do something in a classroom,” she says. “I didn’t realize I had poor spatial skills.”

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Sorby was far from alone. After decades of research, spatial cognition has emerged as one of the few areas where women do not perform as well as men on tasks like mental rotation or “wayfinding,” orienting oneself in physical space. Controversially, that difference has been used to explain a gender imbalance in STEM (science, technology, engineering, and math1) fields. Nationwide, 1 in 3 university professors in the United States are women, but women make up just 1 in 5 science and engineering professors.

More recent studies, though, have clarified the gap in spatial abilities. The difference has been forged in large part by cultural forces, say scientists, and can be overcome. The plasticity of the brain allows women to improve and enhance their spatial abilities, says Sorby—once they’re given the right tools. “This could be a big piece of the puzzle in terms of getting more women into engineering,” she says.

Men are significantly better than women at mental rotation, particularly in three dimensions.

Psychologists long took it for granted that the male and female brains were fundamentally different. But in a landmark 1974 book, Stanford developmental psychologists Eleanor Maccoby and Carol Jacklin reviewed thousands of studies and found the opposite: By and large, there just wasn’t much data to support the conventional wisdom. Yes, men’s brains are bigger, but so are their bodies; aside from size, there’s no solid evidence of physical characteristics in the brain that are demonstrably male or female. A 2015 study published in the Proceedings of the National Academy of Sciences concluded that “human brains do not belong to one of two distinct categories: male brain/female brain.”

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Yet over the years, research has documented differences in cognitive abilities between men and women, something Maccoby and Jacklin noted in 1974. And spatial skills, says Elizabeth Cashdan, an anthropologist at the University of Utah, “are the largest cognitive sex difference known.”

Take the projection problems that Sorby struggled with in her engineering graphics class. They draw on the ability to look at a shape and imagine it from different angles and perspectives. Men are significantly better at mental rotation, particularly in three dimensions; they’re also measurably superior at “targeting,” which one researcher defines as “the ability to aim projectiles accurately at a specified point in space.”

ROTATE THIS: George M. Bodner, a chemical education professor at Purdue University, co-designed a spatial-ability test, featuring the exercise above, to help chemistry students. “The test was a good measure of an individual’s ability to handle spatial tasks as a ‘gestalt’—thinking in terms of the whole figure—rather than by ‘analytic’ processing, following one part of the item at a time,” he says. (Answer at bottom of article.)Courtesy of George M. Bodner

Maccoby and Jacklin also found differences in math and verbal abilities. But data has since shown that spatial cognition might explain some of the gender gap psychologists measured in mathematical ability. High scores on mental rotation tests correspond to higher scores on math questions that involve geometry or story problems. And spatial cognition turns out to be a better predictor of success in engineering than SAT or GRE scores, for example.

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So what explains the gap? Significantly, the differences in spatial cognition are widespread, and have turned up in tests around the world. They’re so prevalent in so many cultures that they can’t be explained purely as an artifact of Western child-rearing practices or education.

“If it was only cultural, it should be different in some cultures. It has to be some kind of biological factor, whether it’s hormones or evolution,” says Sorby. “Maybe it starts out as a small biological difference that grows bigger because of the environment.”

Psychologists have looked at girls born with a genetic condition known as congenital adrenal hyperplasia, or CAH, in which haywire adrenal glands produce high levels of hormones like testosterone. Although it’s usually treated after birth, women exposed to high levels of testosterone in the womb have been studied as a sort of natural experiment to see if hormones can explain some of the gender gaps in cognitive abilities. It turns out women with CAH mutations perform better on mental rotation tests than their sisters without it, suggesting that even when you control for upbringing, hormones may be a factor in spatial ability.

Cause-and-effect is tough to tease apart, though. The differences might mean testosterone has some impact on the development of the hippocampus, the organ most associated with spatial ability. But girls with CAH also show a predilection for “boy toys” like blocks. Perhaps hormones nudge kids toward a set of preferences that develops their skills in certain areas more than others, a phenomenon society amplifies and encourages.

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Cashdan says there might be an evolutionary basis for the gender gap. She’s looked at cultures around the world—and considered research into the behavior of other species, from cowbirds to cuttlefish—and concluded that males range farther afield than females, traveling farther and into less familiar territory over their lifetimes.

The powerful lesson: While gender gaps in spatial cognition are real, they’re not fixed.

Her basic premise is that men have evolved to wander, in search of both food and more mates. Males who travel more and farther have a reproductive edge—as do women who stay closer to home, focusing on protecting and raising their offspring. Studies of traditional and modern human societies have demonstrated larger ranges correspond to better spatial cognition, both in mental rotation and with wayfinding, the ability to navigate and find one’s way around.

It’s still unclear whether a predilection to wander may help men develop better spatial cognition skills—or whether better spatial cognition skills make their peregrinations possible. “We don’t know what’s cause, and what’s effect,” Cashdan says. What is clear is that cultural biases have an effect. Consciously or unconsciously, girls are nudged away from activities that would help them develop spatial skills almost as soon as they’re born. As they grow, parents respond to their kids’ interests, quickly compounding what may start out as very slight biases.

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“Parents are very invested in gender differences, and any differences between a son and a daughter tend to be attributed to sex,” says Lise Eliot, a neuroscientist at the Chicago Medical School of Rosalind Franklin University of Medicine and Science, author of Pink Brain, Blue Brain: How Small Differences Grow into Troublesome Gaps, and What We Can Do About It.

Over time, “boy” toys reinforce skills that are proven brain boosters. Playing with Legos and blocks, taking a shop class in high school and time spent playing 3-D computer games have all been shown to boost scores on mental rotation tests.

SORBY’S CUBE: When she was a student, Sheryl Sorby, a professor of engineering education at Ohio State University, was frustrated to learn she had poor spatial skills. To help students like herself, she has developed a course, featuring the test above, that has brought women even with the baseline for men on basic spatial cognition tests. (Answers at bottom of article.)Courtesy of Sheryl Sorby

Ultimately, separating nature from nurture may be impossible. But Sorby and others who study gender differences say it may not matter. Nora S. Newcombe, a cognitive and developmental psychologist at Temple University, who has researched gender differences in spatial cognition, bristles at the concept that the dearth of women in science is due to hard-wired deficiencies. “I think there might be a biological mechanism, but it doesn’t seem that important in terms of human potential,” she says. “It seems like an excuse.” An excuse not to do the hard work necessary to improve in places we might be lacking.

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Moreover, while comparing the cognitive performances of men and women may produce a measurable difference, the averages don’t tell the whole story. “Many women have significantly stronger spatial ability than many men,” explains George M. Bodner, a professor of chemical education at Purdue University, who designed one of the tests commonly used to measure spatial cognition ability. Bodner stresses it’s important not to perpetuate the myth that a gender gap implies all men are better than all women at spatial cognition tasks. Stereotypes about spatial ability can have an insidious effect. “When women hear myths, such as the idea that they have ‘poor spatial ability when compared with men,’ they often believe this will be true for themselves, and it often is not true,” Bodner says.

Had Sorby been a little less stubborn, she might have left engineering altogether. Instead she went on to earn a bachelor’s and then a Ph.D. in mechanical engineering from Michigan Tech, and was later hired as a faculty member. As Sorby took more engineering courses, she got better at spatial cognition tasks, until eventually she found herself teaching engineering graphics, the very course that almost derailed her as an undergrad. “The brain is pretty plastic when it comes to spatial skills,” Sorby says. “I have improved my spatial skills vastly as an adult.”

That initial experience never left her, though. As a professor, she noticed talented young women struggling the way she had. So she set out to find a solution. “The fact that there are these gender gaps is a challenge, but it’s not a death sentence,” she says. “I know it’s something we can fix.”

With her colleague, Beverly J. Baartmans, she developed a spatial visualization course to help her students develop their spatial cognition skills. The 15-hour program—which uses blocks, sketching, software, and workbooks full of practice exercises—brought the women who took it even with the baseline for men on basic spatial cognition tests and helped boost retention rates for female engineering students by 20 to 30 percent. “If you start with 100 women, you’d expect 50 to graduate as engineers,” Sorby says. “If we give them this intervention, 80 will graduate from engineering.”

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Exercises that connect motion and gesture to visualization—manipulating blocks to sketch them from different angles, for example—seem to have the biggest impact, whereas computer exercises alone didn’t move the needle at all. “Sketching seems to really help,” Sorby says. “Gesturing and using your hands helps you visualize.”

Newcombe offers that programs like Sorby’s might change the way our brains work on the sub-cellular level. “Plasticity is about functional connectivity, or what you’re doing with the brain you have,” she says. “Individual neurons might grow or lose inputs and outputs, or change chemically at the synapse level.” The powerful lesson: While gender gaps in spatial cognition are real, they’re not fixed. “For most cognitive abilities, there are extended periods of plasticity—maybe infinite,” Newcombe says. “Everybody can get better.”

Everybody means men, too. Sorby’s program, for example, improved the spatial skills of male engineering students as well, boosting their scores on tests. Because they start out ahead of their female counterparts, their gains often put them ahead on spatial cognition tests after the course. However, Sorby says, the course has made a small difference in retention rates for men, “but we’re seeing a big difference for women.”

Sorby is still not sure what exactly is going on in the brain. She has just begun an experiment to see if her program results in brain changes, as measured by fMRI brain scans. “It’s important to know the why, and not just the how,” she admits. But for now she remains pleased by what she has learned. “We have this intervention, and we know it works,” she says. “We know with 15 hours of instruction, girls are much more likely to graduate from engineering.”

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Andrew Curry is a journalist in Berlin, Germany. He has written for a wide range of publications, including Archaeology, Discover, National Geographic, and Wired. You can follow him on Twitter @spoke32

Additional Reading

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Casey, M.B., Nuttall, R., Pezaris, E., & Benbow, C.P. The influence of spatial ability on gender differences in mathematics college entrance test scores across diverse samples. Developmental Psychology 31, 697-705 (1995).

Cashdan, E. & Gaulin, S.J. Why go there? Evolution of mobility and spatial cognition in women and men: An introduction to the special issue. Human Nature (2016). Retrieved from doi: 10.1007/s12110-015-9253-4

Humphreys, L.G., Lubinski, D., & Yao, G. Utility of predicting group membership and the role of spatial visualization in becoming an engineer, physical scientist, or artist. Journal of Applied Psychology 78, 250-161 (1993).

Joel, D., et al. Sex beyond the genitalia: The human brain mosaic. Proceedings of the National Academy of Sciences 112, 15468-15473 (2015).

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Linn, M.C. & Petersen, A.C. Emergence and characterization of sex difference in spatial ability: A meta-analysis. Child Development 56, 1479-1498 (1985).

Maccoby, E.E. & Jacklin, C.N. The Psychology of Sex Differences Stanford University Press, Palo Alto, CA (1974).

Puts, D.A., McDaniel, M.A., Jordan, C.L., & Breedlove, S.M. Spatial ability and prenatal androgens: Meta-analysis of CAH and digit ratio studies. Archives of Sexual Behavior 37, 100-111 (2008).

Voyer, Dd., Voyer, S., & Bryden, M.P. Magnitude of sex differences in spatial abilities: A meta-analysis and consideration of critical variables. Psychological Bulletin 117, 250-270 (1995).

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Test Answers
Rotation: B. 
Cube: 1) Far-right box; 2) Top box; 3) Far-right box; 4) Middle box; 5) Middle box; 6) Far-left box.

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