Forget Venus and Mars, we’re beginning to understand gender behavior on Earth

Gender gaps permeate nearly every aspect of our culture, as everything from comic books to the constitution seems to stress the differences between men and women rather than any similarities between the sexes. It’s hard to walk through a bookstore without being bombarded with advice on decoding the other sex’s cryptic behavior; a few classics are Men are from Mars, Women are from Venus, The Female Brain, and the ever-so-helpful Guys are Waffles, Girls are Spaghetti. Sitcoms, romantic comedies, and action movies all tend to exploit traditional gender roles too: females worry, nag, and primp while males theorize, womanize, and ride to the rescue.

Unfortunately, the actual science behind gender gaps isn’t nearly as clear cut. It’s a miasma of conflicting results, non-replicable studies, and varying effect sizes. And when you think about the complexities involved, it’s no wonder there’s a lot of confusion. Researchers studying gender differences must deal with genetics, physiology, behavior, culture, age, environment, race, and innumerable other variables. Behavior is also extremely sensitive to context, which muddies the waters further. Evaluating and interpreting the differences between men and women is, simply put, no easy task.

Sex itself is complex. We already know that sex in the animal kingdom is a surprisingly fluid concept, and that sex determination is more complicated than a single chromosome. In this third installment of our continuing series on sex and gender, Ars is bringing you some of the more promising research into what—if anything—separates males from females when it comes to behavior.

It’s all too easy to fall back on the clichéd metaphor that men and women hail from different planets, or the popular but sketchy evo-psych claims that trace every aspect of our behavior back to our origins on the African savannah. Here, we’ll steer clear of these overhyped and underwhelming points of view. Instead, we’ll take a look at some of the good science that is beginning to separate truth from fiction in regard to gender gaps. Some of this research is creative, some is elegantly simple, and some is complex and nuanced. But these studies are all promising in terms of identifying gender gaps, hinting at their origins, and suggesting how we might use this knowledge in the future.

Beginning at the beginning

Despite the difficulties inherent in studying gender gaps, it’s an important task, because what we know (or think we know) about these gaps actually affects how we behave. Teachers treat and evaluate male and female students differently. Females’ test performance drops when they are told that men generally score better on the test than women. Both men and women tend to fulfill cultural expectations regarding their gender, even when it comes to something as simple as smiling. Our awareness and understanding of sex differences do matter, because—either intentionally or unintentionally—we use this knowledge to inform our behavior and the behavior of others.

The first major question that needs to be asked is whether gender gaps actually exist, or whether they are merely a figment of our collective imagination. Not surprisingly, the evidence is mixed.

A large and rigorous study published recently in PLOS ONE found larger than expected gender differences in personality worldwide, including significant gender-based differences in sensitivity, warmth, apprehension, dominance, and rule consciousness. The researchers calculated an overall overlap of just 10 percent in the distribution of males’ and females’ personalities. That’s a huge difference, in psychological terms.

However, psychologist Janet Shibley Hyde conducted a meta-analysis that challenged the notion that men and women are so vastly different. After evaluating 46 studies of psychological gender differences ranging from cognition to personality to self-esteem, Hyde identified just a few areas in which men and women differed significantly. These include physical aggression, motor skills, and measures of sexuality (such as the frequency of masturbation). But for the vast majority—78 percent—of the traits and behaviors she examined, Hyde found little or no difference between the sexes. Men and women, she argued, are more alike than they are different.

More Kate Shaw Yoshida on gender

September 2012: Pregnant males and pseudopenises: complex sex in the animal kingdom
November 2012: Shifting sexes and sequential hermaphrodites: How sex is determined So, no consensus there. And uncertainty is the norm when it comes to research on gender gaps in cognition and behavior. A quick literature search shows that self-esteem does and doesn’t differ between males and females, that men are and are not better at reading maps, and that there are and are not differences in how the two sexes use language and vocabulary.

Depending on the methodology, the context, and the subtleties of the questions being asked, there are very few solid generalizations we can make about gender differences between men and women. There are a few widely-accepted differences: men are more aggressive and more likely to commit crimes than women are, and women are more prone to anxiety and are more likely to be diagnosed with depression than men are.

If evaluating the extent of sex differences seems complicated, the next step is even more difficult: figuring out where gaps originate. Are differences between men and women innate, dictated by our DNA and our evolutionary history? Or are they a product of our culture and the experiences and interactions we have?

A search for the biological roots of gender gaps

At first, the answer seems obvious. To figure out where these gaps originate, start with our brains. And there’s no question that there are biological differences in the brains of men and women; the sexes differ in the size, symmetry, and activation of several major brain regions, as well as the amount of gray and white matter in the brain.

But one of the major stumbling blocks in understanding gender gaps is that “biological” differences aren’t necessarily equivalent to innate, “hardwired” differences. The brain is a malleable organ that changes over time in response to a person’s experiences, exposures, and opportunities. For instance, practicing karate can enlarge part of the brain responsible for motor skills and coordination, and the more a person listens to music, the more sensitive their auditory system becomes. This plasticity is just one of the many reasons why it’s extremely difficult to determine whether there are quantifiable innate differences between the brains of men and women. Differences in brain structure or function don’t necessarily indicate that gender gaps are based deep in our genes or our evolutionary history.

But despite the challenges, researchers have tried to tackle some of these difficult questions. One way to determine whether biology is at the root of a sex difference is to limit the influence of experience as much as possible. By studying the brains and behavior of infants, scientists can try to look at “nature” before “nurture” has a chance to intervene.

A relatively large body of literature suggests that in even very young children, females perform better than males in tests of social cognition (that’s the scientific term for the skills that go along with understanding and relating to other people). Of course, since newborns can’t answer surveys or perform complicated tasks, testing social cognition in infants requires the use of simplified proxies such as eye contact. Females as young as just a few days old tend to make more eye contact than males do, and girls this age are better at imitation than boys are. Another study tested whether infants pay more attention to a face or a mechanical object, such as a mobile. At just 36 hours old, newborns of each gender already have very definite preferences: baby girls show more interest in a human face, while baby boys show more interest in the mobile than the face. At three months of age, females show more expressions of interest, such as wider eyes and raised brows, in response to people than males do.

A group of researchers hypothesized that there may be a genetic component to these sex differences in social skills; they reasoned that females may inherit their social awareness from the paternally-contributed sex chromosome. At first, this seems backwards: if females have better social skills, shouldn’t social awareness be passed on maternally, from mother-to-daughter, rather than paternally, from father to daughter?

But think about it: females normally receive two X chromosomes (one from each parent), while males only inherit a single X chromosome (from their mother). If one of these X chromosomes confers an advantage in terms of social skills, it’s the one from dad that is unique to females, not the one from mom, which both sexes get.

To test this theory, the researchers took advantage of Turner syndrome, a chromosomal disorder in which females have just one X chromosome which can be inherited either from their mother (called Xm, for maternally-inherited) or from their father (called Xp, for paternally-inherited). If social awareness is a product of the paternally-contributed X-chromosome, Xp females should be more socially savvy than Xm females. And that’s exactly what the researchers found: on social awareness tests, Turner females with a paternally-inherited X chromosome greatly outperformed the females whose chromosome came from their mom.

The researchers reason that the maternally-inherited X chromosome is epigenetically silenced, potentially through the addition of methyl groups. And this isn’t as far-fetched as it sounds. It’s called genomic imprinting, and it’s known to occur in a handful of mammals. Alleles from one parent (in this example, the mother) are silenced, while those from the other parents (here, the father) are expressed.

However, further investigations of this phenomenon, at least in terms of gender differences in social cognition, have been inconclusive. A more recent study did not find the same pattern of chromosomal inheritance and social cognition; in fact, some of the results were actually reversed from the previous study. While the original study has been replicated (but not published) by the original authors, the scientific community is still split on the controversial idea that genomic imprinting plays a role in the social cognition gender gap.

Studying another genetic abnormality called congenital adrenal hyperplasia, or CAH, has provided solid evidence that biology plays a role in shaping early behavioral differences between boys and girls. Generally, toy preferences in human children are attributed to cultural pressure and socialization; adults encourage girls to play with dolls and boys to play with trucks. But a group of researchers wondered whether sex-specific play behavior might also be influenced by hormones.

People with the classic form of CAH experience very high levels of masculinizing hormones called androgens in utero, thanks to an inability to produce certain enzymes. The authors hypothesized that if androgen exposure affects toy preferences, girls with CAH might prefer traditionally “male” toys over stereotypically “female” toys.

And they were right: 3- to 8-year old girls with CAH spent much more time playing with toys generally considered to be “boys’ toys”—including a helicopter, a fire engine, and Lincoln Logs—than with “girls’ toys” such as dolls and kitchen supplies. In fact, these girls spent just about as much time playing with these toys as boys did.

Although it’s possible that this is a product of the girls’ upbringing, other studies have found that parents of girls with CAH don’t encourage their daughters to play with opposite-sex toys. In fact, they praise these girls more when they do play with “feminine” toys. Therefore, these results provide rather convincing evidence that hormone exposure may dictate toy preferences in girls with CAH and potentially in the rest of the population as well.

Studies in other species, such as rhesus and vervet monkeys suggest that other primates may share humans’ sex-specific toy preferences, lending even more weight to a biologically-based explanation.

The role of “nurture”

So, there is some evidence that biology plays a role in male-female behavioral differences via our genes and our hormones. But how influential is, well, everything else?

If the environment played no role in sex differences, gender gaps should be consistent across cultures. But this isn’t what researchers find; behavioral differences between men and women range widely—and sometimes disappear—in other countries. In Turkey, Korea, and Italy, the mathematics gender gap is large, and boys do much better than girls do on standardized math tests. In Iceland, there is also a large gender gap when it comes to math, but here, girls, not boys, score the best. In Norway and Sweden, there is almost no difference in the performance of boys and girls. These differences appear to be correlated with a general measure of gender inequality in each country, as calculated by the World Economic Forum. Countries where women are politically and economically empowered have the smallest sex differences, at least when it comes to math. However, these countries also have the largest gender gaps in reading, and here, girls actually outperform men. In both cases, it’s clear that a simple biological explanation doesn’t cut it. There is a definite relationship between sex differences in test performance and the cultural milieu of different nations.

Researchers found a similar phenomenon when they looked at spatial reasoning among members of two tribes in India. The tribes are closely related in terms of genetics but differ greatly in their social structures: the Karbi are patrilineal (inheritance passes from father to son, and most rights belong to men, not women), while the Khasi are matrilineal (inheritance passes from mother to daughter, and women are more empowered than men). Among the patrilineal Karbi, men were much better at a spatial rotation task than women. However, when it came to the matrilineal Khasi, women outperformed men on the puzzle. (See Ars’ previous coverage on this study for more information.)

Many studies also find that situational factors play a large role in whether or not men and women demonstrate measurable differences in behavior. Simply asking for a participant’s gender can cause differences in performance; women tend to do better on verbal tests and worse on math tests after being asked their gender. By making people think about their gender (increasing its “salience,” in psychology parlance), researchers believe that they are triggering a tendency to conform to traditional gender stereotypes.

Note, however, that none of the studies advocating the role that culture and environment play in gender gaps actually rule out an evolutionary or biological contribution. As un-PC as it may be, it’s nearly impossible to believe that over our evolutionary history, the brains and behavior of men and women have not succumbed to different selective pressures. In the natural world, species from hummingbirds to hyenas demonstrate remarkable differences in the behavior of each sex. Is it so hard to believe that men and women have evolved to behave differently from one another?

However, the truth probably lies somewhere in the middle; our evolutionary history may have selected for differences in the behavior of males and females, but they aren’t of the “Mars-Venus” magnitude that pop culture would like us to believe. Furthermore, the influence of the environment on our behavior is so strong that “nurture” likely plays a much larger role in gender gaps than “nature.” It may seem disconcerting that culture can increase—or even spontaneously create—sex-specific differences in our behavior, but this also suggests that we can affect, and perhaps even eliminate, some gender gaps if we see fit.

Shifting gaps

And today, gender gaps are changing. Some gaps are narrowing, others are widening, and still others have reversed. For instance, in 1970, just 42 percent of undergraduates were women; today, women make up 57 percent of the student body at colleges and universities. That number is predicted to grow to 59 percent by 2020. Census data shows that the number of men that have left the workforce to become stay-at-home dads has more than doubled since the early 2000’s. Even our perceptions of gender gaps are changing: earlier this year, the US military lifted the ban on women in combat.

Thanks to an improving body of knowledge about gender gaps, we are starting to understand how and when some sex differences are manifested. And, in turn, scientists, psychologists, and educators are now beginning to figure out how we can manipulate these gaps to affect sex-specific behavior.

For instance, one study suggests that choosing specific test administrators can increase or decrease a gender gap; girls did just as well as boys on a challenging math test when a “female role model” (in other words, a woman that’s good at math) administered the test, but they performed much worse than boys did with a male administrator. Other studies, too, suggest that female role models are an effective way to promote self-confidence in girls when it comes to math and science.

Recent research also suggests that boys and girls respond very differently to repeated contests, compared to single stand-alone competitions. In a “one-shot” math contest, where kids are tested just a single time, elementary school-age boys tend to outperform their female classmates by about 10 percent. However, in a sequential competition where kids are quizzed over multiple rounds, the sex difference disappears. Ironically, however, this actually raises the possibility of another gender gap, since the researchers believe their results may stem from the different way males and females respond to competition.