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Imagine you had some friends over to your place, and they asked how to get to the nearest Starbucks. What kind of directions would you give?
Nowadays, with smartphones and GPS, providing an exact address might be your go-to option. But maybe you’d also note the general distance and cardinal direction of the Starbucks (e.g., “about two miles to the southeast”)? Or perhaps you’d describe key landmarks along the route (e.g., “take this street until you get the McDonalds, take a left, if you end up seeing the hospital, you’ve gone too far”). Which are you more likely to use in helping your friends find the nearest Starbucks, general directions or landmarks?
It turns out, which option you choose may depend, in part, on whether you are a man or a woman. That’s because men rely more on spatial cues like distance and direction when navigating (i.e., they use Euclidean properties). Whereas women are more likely to use landmarks when navigating (Postma et al., 2012; Saucier et al., 2002). Although thinking about men and women as, on average, psychologically different might evoke other gendered stereotypes (like “men never ask for directions”), there is some solid science behind the specific claims about sexual diversity in navigation. How do sexual scientists know this is so?
Well, we don’t know for sure (not yet, this blog concerns existing sexual science and known evidence, not ideological imperatives about whether we must be certain that men and women are, or are not, psychologically identical). As it stands, below are 10 converging lines of evidence suggesting psychological sex differences are probably real, and quite possibly evolved. First, let’s consider the theory that led evolutionary psychologists to predict sex differences in the use of Euclidian properties versus landmarks when navigating. Why expect such a sex difference? What function might it serve?
A Hunter-Gatherer Theory of Sex Differences in Navigation and Spatial Abilities
Silverman and Eals (1992) were among the earliest to argue gendered divisions of labor in our ancestral past, particularly those found in foraging cultures, may have led to sex differences in certain spatial abilities related to navigation. They noted men were much more likely than women to hunt large animals over great unfamiliar distances in ancestral foraging cultures (ethnographic evidence suggests this is so in nearly 100% of pre-industrial cultures from the Standard Cross-Cultural Sample; Murdock & Provost, 1973). As a result, men may have evolved special spatial abilities for thinking about the world in Euclidian terms. In addition, men’s hunting need to accurately throw projectiles at moving targets (Thomas & French, 1985; Watson, 2001), as well as, men’s ancestral tendencies to roam vast distances to defend large home ranges against other humans (Gaulin & Fitzgerald, 1989) may have impacted sex differences in Euclidian thinking and ability. Men who thought most clearly in Euclidean terms, it is hypothesized, out-survived and out-reproduced men who could not (Silverman et al., 2000).
In contrast, women in our ancestral past were primarily involved with gathering immobile food sources within familiar territory (Murdock & Provost, 1973), which likely required superior spatial location abilities (e.g., object location memory) and thinking about the world in terms of landmarks. Where was that bush with especially ripe fruit? It is near the tree we always go to for fresh nuts. Immobile food sources tend to stay put in foraging societies, and perhaps as a result women evolved superior object location memory.
Theoretically, these reliable gendered divisions of labor in our ancestral past would have led to the evolution of sex differences in cognitive navigation strategies (for a review, see Silverman et al., 2007). But how do we evaluate if these sex differences are real? Evolutionary psychologists tend to look for converging lines of evidence (Schmitt, & Pilcher, 2004), but what sources of evidence do we have about sex differences in navigation strategies and spatial abilities?
Evidence Source 1: Cognitive Tests and Surveys
Cognitive tests of people’s navigational tendency to use Euclidian properties versus landmarks generally find men and women do differ in their use of these wayfinding strategies (see Dabbs et al., 1998; Kimura, 1992; Postma et al., 2012). On tests, for instance, men usually are more likely than women to use distance and Euclidian terms—such as using miles/meters and north/south east/west terms—when giving directions (women tend to use more landmark terms), men also are more able than women to identify more faraway places on world maps, and men are better than women at skills related to Euclidian mental wayfinding (Dabbs et al., 1998).
In addition, there are certain cognitive ability tests that are closely related to Euclidean or landmark wayfinding that persistently show very similar degrees of sex difference. For instance, tests of mental rotation ability are related to using Euclidean distance and direction to navigate (Saucier et al., 2002), whereas tests of object location memory are related to using landmarks to navigate. Not surprisingly, most studies using these cognitive tests document that men tend to be better than women at mental rotation, on average, and women tend to be better than men at object location (e.g., Silverman et al., 2007).
Evidence Source 2: Strong Meta-Analytic Confirmation
It’s not just a couple of studies that demonstrate these sex differences in spatial abilities. Not even just a dozen. We’re talking hundreds. Meta-analyses of these sex differences, whether examining findings from the 1970s (Hyde, 1981), the 1980s (Linn. & Petersen, 1985), or the 1990s (Voyer et al., 1995), suggests men’s and women’s differences in mental rotation and object location abilities are highly replicable and real.
How real? Well, the most common metric for evaluating the size of a psychological sex is the “d” statistic. A positive d value of +0.50 indicates men are moderately higher on a psychological measure (+0.20 is a small difference, +0.80 is a large difference), a negative value of -0.50 indicates women are moderately higher and so forth. Meta-analyses suggest the d value for sex differences in mental rotation ability fall in the range of +0.56 to +0.73 (Linn & Petersen, 1985; Voyer et al., 1995), for object location memory d values are smaller and less consistent, but still show up in most studies.
Evidence Source 3: Cross-Cultural Universality
It could be these cognitive sex differences are found consistently, but only in studies college students from the United States. Not so. These sex differences are not limited to just college students or just the United States, or even just cultures from the Western world. Silverman et al. (2007) found sex differences in spatial abilities were pan-culturally universal across samples from 40 nations around the world, from Canada to China to the Czech Republic, from South Africa to Spain to Sweden. Men always have better mental rotation ability, and women always have better object location memory, on average. That doesn’t guarantee the sex differences are evolved, it could be they reflect some sort of pan-cultural gendered socialization practice or pattern of political patriarchy.
However, evidence suggests socialization and patriarchy are unlikely sources of these cognitive sex differences. This is because in the Silverman et al. (2007) study, increasing gender egalitarianism was associated with larger sex differences in object location memory (see Schmitt, 2015). That’s right, in more gender egalitarian cultures where men and women are socialized and educated more equally, sex differences in object location memory don’t get smaller, they get conspicuously larger. Same is true for mental rotation (Lippa et al., 2010; see Figure 1 below and notice the largest sex differences in mental rotation ability are in Norway, smallest in Pakistan).
So much for socialization and patriarchy as an explanation of cognitive sex differences. It appears that in societies where men and women the most free to be who they want to be, they are psychologically the most different (see here).
Evidence Source 4: Hunter-Gatherer Cultures
Cashdan et al. (2012) examined sex differences in spatial abilities among the Hadza, a mobile hunter–gatherer population from Tanzania. This was a special test of sex differences in cognitive abilities, as both men and women among the Hadza are highly mobile, so perhaps men and women both have great Euclidean spatial abilities. Cashdan et al. measured Euclidean spatial abilities using several different tests (e.g., ability to point accurately to distant locations) and found across all three tests that men have better Euclidean spatial abilities. They did find women who were especially mobile tended to do well. They also found, unlike most studies of Western cultures, women were not better than men at tests of object location memory. This was, in part, due to the decline in women (but not men) in object location memory as they age. Cashdan et al. suggested older foraging women seemed to specialize in when fruits will be ripe, rather than where the fruits are located. Timing is everything.
Anthropologists have examined spatial abilities in many other pre-industrial cultures, usually with similar results (e.g., sex differences have been documented among the Twe and Himba people in a remote region of Namibia; Vashro et al., 2016). In a study of the mobility and navigation of the Yucatec Maya, men were less spatially anxious than women, thought themselves to be better navigators, and pointed more accurately to distant locations (Cashdan et al., 2016). Among the Tsimane forager horticulturalists living in lowland Bolivia, however, no sex differences were found when testing for the "dead-reckoning" ability to point to nearby towns (Trumble et al., 2016), a finding that may be explained by the relatively low levels of testosterone among Tsimane men (Trumble et al., 2014).
Evidence Source 5: Real-World Observations
In real-world tests of spatial ability, numerous studies have confirmed men’s superior ability at mental rotation (Lawton, 1996). For instance, several studies of parking ability have shown men park more accurately than women. Wolf et al. (2011) gave beginning and experienced drivers a mental rotation test and assessed their parking skills. Men parked more accurately and especially faster than women. Parking performance was positively related to mental rotation skills in beginners, but not in experienced drivers. Wolf et al. (2011) concluded sex differences in spatial cognition persist in real-life situations.
Postma et al. (2012) investigated men’s and women’s spatial memory of their parking place during an incidental visit to a shopping mall. As expected from an evolutionary perspective, women reported more landmarks in their route descriptions than men, whereas men used metric terms more often than women. Men also outperformed women in estimating the exact Euclidean distance to their car. In actually locating their car in the real world, 14% made a substantial detour, most of them women.
Evidence Source 6: Laboratory Experiments
Moving back to the laboratory, other sexual scientists have used controlled laboratory experiments to evaluate sex differences in navigation strategies. For instance, Moffat et al. (1998) used computer-generated “virtual” mazes to investigate sex differences in the efficiency of learning novel spatial routes. As expected from an evolutionary perspective, men had much better novel route learning within mazes than women. Men took much less time to solve the mazes (d = +1.59) and committed far fewer errors in spatial memory (d = +1.40). Not surprisingly, for both men and women, scoring well on paper-and-pencil tests of mental rotation ability predicted performance on novel spatial route learning in mazes.
In another laboratory, Wiking and her colleagues (2015) gave men and women a mental rotation test and asked them to assemble a kitchen trolley from IKEA. One group received step-by-step instructions, the other a diagram of the finished product. As usual, men had better mental rotation ability. Men also assembled the furniture faster (d = +0.78) and more accurately (d = +0.65) than women. However, the difference in speed was largely due to time spent reading step-by-step instructions. That is, women spent more time reading the instructions, but other than that men and women assembled at about the same time. Wiking and her colleagues concluded men’s better mental rotation ability led them to not need to read the directions as much as women when assembling a three-dimensional object. Either that or men just don’t like to read.
Finally, McBurney et al. (1997) had male and female college students play the commercial game Memory, which required them to recall the location of previously viewed items, and also completed a 20-item mental rotation task. As is typical, men performed better than women (d = +0.67) on the mental rotation task, whereas women outperformed men by a large margin on the memory location task (d = -0.89).
Evidence Source 7: Reliable Developmental Emergence
If sex differences in navigation strategies, and the related skills of mental rotation ability and object location memory, are real and “evolved,” an interesting corollary question is whether the differences are present shortly after birth (due to organizational effects of sex-differentiating hormones on our brains in the womb), whether they emerge at a reliable age in childhood (due to differences in universal lived experiences of children, some of which may be rooted in other evolved differences such sex differences in liking rough and tumble play), whether they emerge most notably at puberty (due to activational effects of sex-differentiating hormone surges linked to reproductive maturity, beards and breasts don’t just come out of nowhere), or whether they regularly emerge during later adulthood (e.g., being reliably evoked only after pair-bonding, or becoming a parent, or menopause, or some other predictable adult life experience; Saxton, 2015).
Finding a sex difference is not present at birth would not mean it is unrelated to our biological evolution (a common mistake made by critics of evolutionary psychology). Even so, determining when the sex difference emerges developmentally is important to know, because the precise timing can give us a clue as to the exact mechanisms behind the sex difference (e.g., pubertal hormone surges), and precisely how evolution accomplishes generating the culturally-universal sex difference (and why it might also vary across time and place due to socioecological factors; Schmitt, 2015). So, what does the developmental evidence show?
Most of the available evidence suggests sex differences in mental abilities emerge very early (Merrill et al., 2016), especially for mental rotation. Studies of children as young as 4 years old have found consistent evidence of these sex differences (Levine et al., 1999). As Linn and Petersen (1985) concluded in a meta-analysis, “There were no changes in effect size with age over the ages studied. Sex differences are detected as soon as mental rotation could be measured.” (p. 1488). In one ingenious study, researchers were able to test pre-verbal infants who were only 5 months old using habituation and mirror images. They found male infants, but not female infants, showed the ability to rotate and recognize mirror image objects (Moore & Johnson, 2008). The early emergence of sex differences in mental rotation ability suggest organizational effects are a likely cause of the sex difference, though other experiences also play a role in the intensity of their emergence (Lauer, Yhang, & Lourenco, 2019).
Relatedly, similar results have been found with studies on the very early emergence of play behavior and toy preferences. In a study of 3- to 8-month olds, girls fixated more on dolls than trucks (d = -1.27), whereas boys fixated more in trucks than dolls (d = 0.39). And the number of fixations on the doll was greater in girls compared to boys (d = -0.29), with fixations on the truck significantly greater in boys compared to girls (d = 0.78). In another study of 21 male and 20 female 3-month olds, the higher the testosterone levels of male infants (but not female infants), the greater the interest in male-typical play preferences (Alexander et al., 2009b). Alexander and her colleagues (2009a) concluded, "Our findings suggest that the conceptual categories of “masculine” and “feminine” toys are preceded by sex differences in the preferences for perceptual features associated with such objects."
Evidence Source 8: Psychophysiology and Neuroscience
So far, we’ve evaluated evidence showing men and women tend to use slightly different navigation strategies, and that several navigation-related cognitive abilities, such as mental rotation ability and object location memory show very similar patterns of sexual differentiation. Many of these sex differences have been confirmed using meta-analytic techniques and appear to be pan-culturally universal in very large international studies (and, moreover, the size of the sex difference are typically largest in the most gender egalitarian nations of Northern Europe, so patriarchy and intense gender-role socialization are unlikely sources of psychological sex differences; Schmitt, 2014). Sex differences in cognitive abilities have been documented in foraging cultures, and have been found in studies of real-world behavior (e.g., car parking) and across numerous laboratory experiments (e.g., constructing IKEA furniture). Sex differences in cognitive abilities appear to emerge very early in life (as young as 5 months), suggesting there are organizational effects of hormone exposure in utero that give rise to at least some cognitive sex differences.
Several additional sources of evidence suggest sex differences in navigation and spatial abilities are rooted in physiological and neurological differences between men and women, much of it related to sex hormones.
Testosterone versus Estrogen
Silverman et al. (1999) found among men that mean levels of testosterone are related to mental rotation abilities, but not to other non-navigation related cognitive traits. Other researchers have found similar results (e.g., Kimura & Hampson, 1994). General circulating levels of estrogen, in contrast, appear to improve performance on object memory games, but reduce performance on Euclidean spatial tasks. Although this pattern of evidence is found in most studies, sometimes extreme variations in testosterone and estrogen show curvilinear results (see Kimura, 2002; Kimura & Hampson, 1994).
Women’s normal hormonal variations across the menstrual cycle also correlate with their performance on mental rotation tests (Chabanne et al., 2004; Hausmann et al., 2000; Noreika et al., 2014). For example, Hausmann et al. (2000) collected blood samples in 3-day intervals over six weeks from 12 young women with regular menstrual cycles. A significant cycle difference in spatial ability (on the Mental Rotation Test) was found, with high scores during the menstrual phase and low scores during the midluteal phase. Testosterone had a strong and positive influence on mental rotation performance, whereas estradiol had a negative one. Noreika et al. (2014) found men were more accurate and had quicker reaction times than women at a mental rotation task, but women in the midluteal phase phase of their menstrual cycle (LU; when progesterone is at its highest) were especially slow in reaction time compared to men and to women in their early-follicular phase (FO; see chart below).
Experiments in which hormones are manipulated also tend to confirm evolutionary perspectives on sex differences in cognitive abilities. For instance, in a double-blind placebo-controlled study, a single sublingual dose of 0.5 mg of testosterone significantly improved healthy young women’s performances on a mental rotation task (Aleman, Bronk, Kessels, Koppeschaar, & van Honk, 2004).
Testosterone Exposure in the Womb
As noted earlier, the emergence of cognitive sex differences at very young ages (as young as we can measure, 5 months so far), suggests sex differences stem, in part, from organizational effects of hormones experienced in utero. In humans, a critical period exists between 12 and 22 weeks of gestation during which male brains, but typically not female brains, are permanently altered in both structure and function in ways that result in masculinized personalities, cognitive abilities, and play behaviors (Baron-Cohen, 2004; Cohen-Bendahan, van de Beek, & Berenbaum, 2005; Pasterski et al., 2005; Udry, 2000).
Several studies have found the level of testosterone a girl is exposed to in the womb predicts her subsequent spatial abilities (Grimshaw, Sitarenios, & Finegan, 1995; Hampson, Rovet, & Altmann, 1998), with higher levels of testosterone exposure typically leading to better mental rotation ability.
In addition, some girls are exposed to especially high levels of testosterone in utero. These girls experience what is called Congenital Adrenal Hyperplasia (CAH) and their brains are more masculinized relative to other girls (even their own sisters). Not surprisingly, CAH girls tend to be better at targeting and mental rotation tasks. In one study, CAH girls outperformed other women in dart throwing (d = +0.64) and slightly in mental rotation of 3D objects (d = +0.17; Hines et al., 2003). A meta-analysis of studies linking CAH and spatial abilities in women found overall effect sizes likely range between +0.30 and +0.60 (Puts et al., 2008; cf. Collaer & Hines, 2020). More recent evidence, though, suggests this may depend on the subtype of CAH (Hampson & Rovet, 2015), concluding "Only females with the more severe, salt-wasting form of CAH, but not females with the simple-virilizing form, performed significantly better than sex-matched sibling controls on measures of mental rotation".
Prenatal testosterone exposure, as well as, the degree and timing of pubertal testosterone surges in boys, also appear related to features of mental rotation (Shirazi et al., 2020), including sex-specific aspects of brain lateralization linked to mental rotation (Beking et al., 2017). Similar results are found regarding toy preferences, with CAH girls displaying a boy-typical pattern, playing more with boy toys (350 seconds) than girls toys (90 seconds; Berenbaum & Hines, 1992), with the degree of testosterone exposure among “typical” boys & girls correlating with sex-typical toy interests as well. Spatial abilities also appear related to the degree of masculinity in both boys and girls (Signorella & Jamison, 1986).
Brain Structure and Activation Patterns
Researchers have found significant sex differences in the brain activation patterns among men and women when they perform mental rotation tasks (Jordan et al., 2002; Satterthwaite et al., 2014). Men also appear to have different parietal lobe structure than women in ways that impact mental rotation abilities (Koscik et al., 2009). Interestingly, men who are very good at mental rotation tend to use more of their parietal lobe when mentally rotating objects, whereas high ability women generally use more of their frontal lobe when mentally rotating objects. With special training (e.g., 18 hours of origami training), high ability women start to use more of their parietal lobe (Jaušovec & Jaušovec, 2012).
Evidence Source 9: "Natural Experiments"
Nature provides a wonderful spectrum of gendered expression that allows researchers to disentangle, to some degree, the origins of sexual diversity. For identifying the causes of sex differences in spatial abilities, four such “natural experiments” are particularly relevant—the fact that humans sometimes have twins in which a male and female share the same womb (Vuoksimaa et al., 2002), the fact that humans display a wide range of sexual orientations that have identifiable biological substrates (Rahman, 2005), the fact that some people may have sex-typed brains that do not match their biological bodies and who have physiologically transitioned to become the opposite sex (Bailey, 2003), and the fact that some people have genes that do not match their hormonal experiences (van Hemmen et al., 2014). Each of these groups provides a special evidentiary window into the origins of sex differences in spatial abilities.
Twins
As noted earlier, when boys are in the womb, their brains become masculinized after exposure to testosterone during the second trimester. In the case of a brother-sister twin combination, the female co-twin is also exposed to higher levels of male hormones than other girls. As a result, it might be expected that women who shared a womb with their twin brother would be better at mental rotation tasks. Indeed, they are (though the effect is small, d = +0.14; Vuoksimaa et al., 2010).
And it may depend on the specific type of rotation task (Toivainen et al. 2018). Using a rather large sample of twins, Toivainen et al. (2018) found that although women with a male co-twin had better overall spatial abilities than women with a female co-twin (d = +0.19), this difference was bigger for Elithorn Mazes (d = +0.21) than it is for paper folding tasks (d = +0.10).
Sex Orientation Variability
Another “natural experiment” of sorts is to look at how sex differences in spatial abilities vary across sexual orientations. Although gay men and lesbians are largely subjected to the same gendered socialization practices that heterosexuals are within a given culture (Udry, 2000), there is some evidence that gay men tend to have slightly more feminized psychologies, and lesbians tend to have slightly more masculinized psychologies (see Cohen, 2002; Rahman, 2005; Schmitt, 2007).
In the case of spatial abilities, researchers have found much the same thing. For instance, Rahman and Wilson (2003) gave a mental rotation test to samples of straight men, straight women, gay men, and lesbians. Out of a possible 40 correct responses, straight men averaged 30 correct, lesbians 25, gay men 24, and straight women 22. This pattern is found across numerous studies (Peters, Manning, & Reimers, 2007; Xu, Norton, & Rahman, 2017; Rahman et al., 2017), and converges with all the other data showing there may be a biological source to human sex differences in cognition.
The mental rotation abilities of bisexuals are also supportive of this view. Peters et al. (2007) found bisexuals tend to be intermediate between same-sex heterosexuals and homosexuals on mental rotation abilities. For men, the difference between bisexual men and other groups was significant both for comparisons with heterosexual men and with gay men. For women, difference between bisexual and lesbians was not significant (but both better at mental rotation than heterosexual women; sample sizes here were very large, N = 134,317 men and 120,783 women).
Relatedly, among bisexual men, Cohen (2002) found the less the men had homoerotic orientations (finding male bodies attractive), the better they did on mental rotation tests.
In studies of sexual orientation and "third gender" individuals, straight men tend to do better than other men (Thurston et al., 2021; see chart below).
Transsexuality
Several studies have investigated mental rotation abilities across transsexual populations. In general, studies of male-to-female transsexuals (MFTS) compare three groups: 1) non-transsexual men, 2) MFTS before undergoing hormone treatment, and 3) MFTS who have undergone hormone treatment. Schöning et al. (2010) examined brain activation during mental rotation across all three groups and found non-transsexual men were better at mental rotation than the other groups and used more of their left parietal cortex, a key region for mental rotation processes. Schöning et al. concluded there are a priori differences between non-transsexual men and MFTS caused by different neurobiology and these differences remain stable over the course of hormonal treatment. Others have similarly found MFTS have more female-typical brains when it comes to spatial abilities (Carrillo et al., 2010; Cohen-Kettenis et al., 1998; Van Goozen et al., 2002), and that the degree of testosterone after treatment relates to mental rotation ability (Sommer et al., 2008).
CAIS
Women who have complete androgen insensitivity syndrome (CAIS)--women who have a 46,XY karyotype but a female phenotype due to a complete androgen resistance--enable researchers us to study the separate effects of gonadal hormones versus sex chromosomes on neural sex differences. As noted earlier, there sex differences in neural activation during mental rotation, with men showing more activation in the inferior parietal lobe than control women. Individuals with CAIS show a female-like neural activation pattern in the parietal lobe, indicating feminization of the brain in CAIS (van Hemmen et al., 2014). This neuroimaging evidence suggests sex differences during mental rotation are most likely not directly driven by genetic sex, but rather reflect gonadal hormone exposure. Similar results have been found for play preferences, with CAIS women preferring more feminine play (whereas CAH women [noted earlier as exposed in utero to high levels of androgens] preferring more masculine play, as noted in chart below; Khorashad et al., 2018).
Evidence Source 10: Comparative Animal Studies
The last source of evidence we’ll briefly consider is how human sex differences in cognition compare to sex differences in other animals. Presumably, sex differences in navigation, mental rotation, and object memory should only be apparent in species where males and females experienced ancestral selection pressures that would cause such differences. And generally, that’s what evolutionary biologists have found (for reviews, see Gaulin & Fitzgerald, 1989; Geary, 1995; cf Clint et al. 2012).
It also found that experience matters in non-human animals, but that experiences might have different effects on males and females (Puts et al., 2007). For instance, although there is only a small difference in maze test performance among males and females in many species, these differences get larger across repeated testing. In Morris water maze performances, on the first trial differences between high androgen groups (e.g., intact males or T-treated females) and low androgen groups (e.g., castrated males, control females) are small, but differences between high- and low-androgen groups get larger across trials. In seasonal breeders like prairie meadow voles, increased testosterone during the breeding season causes males to increase their home range size and to perform better in on mazes in the lab (Puts et al., 2007). Experiences matter, but they matter differently, in part, depending on one's sex.
Also, related results are found with regard to play preferences among males and females of several non-human primates. Among 4-year old vervet monkeys, females play with dolls (21% contact time) more than police cars (8% contact time). Males play with police cars (16% contact time) more than dolls (9% contact time; Alexander & Hines, 2002). In 34 rhesus monkeys, females had more total interactions with feminine toys (about 8) compared to masculine toys (about 7). Males had more interactions with masculine toys (about 10) compared to feminine toys (about 2; Hassett, Siebert, & Wallen, 2008).
Exceptions and Boundary Conditions
It’s important to point out that spatial abilities in men and women overlap far more than they are different. Ethically, it is important to neither dismiss sex differences that are real, nor to overstate their size or importance (Lawrence & Rieder, 2007). Spatial abilities also are highly susceptible to training (Uttal et al., 2013; Schmidt et al., 2016) and contextual factors (Moe, 2018; Tarampi et al., 2016).
For instance, Sanchis-Segura et al. (2018) found STEM majors have much better mental rotation than humanities majors, but that no sex differences are found within each of the two types of majors (i.e., STEM men do not differ from STEM women in mental rotation ability, humanities men do not differ from humanities women in mental rotation ability). However, if you suggest to college students that a mental rotation task has been "optimized for men" in a way that enhances men's performance, men who are humanities majors do better than women who are humanities majors (while there are no effects on STEM majors, nor are there any effects if you suggest a mental rotation task has been "optimized for women"). A meta-analysis of these sorts of "stereotype activation" effects, however, found that overall there are "no significant effects of stereotype threat on men's or women's spatial performance" (Doyle & Voyer, 2016).
Also, some studies do find differences across men and women, even if they are STEM majors. Moè et al. (2018), for instance, found women in STEM degrees who preferred spatial toys as children performed better in mental rotation compared to other women. But men STEM majors had higher mental rotation abilities than STEM women, regardless of whether the men preferred spatial toys as children.
Even so, it's important to acknowledge the frequently observed sex differences in cognition, whether men’s advantages in mental rotation ability or women’s advantages in object location memory, are probably modifiable in certain circumstances if we choose to actively intervene in the lives of boys and girls, and men and women (Bosco et al., 2004).
In addition, there are several reasonable concerns with some of the methods used to test sex differences in cognition, including sex differences in mental rotation ability. For instance, Ruthsatz et al. (2015) have pointed out many of the most common techniques for testing mental rotation ability rely on stimuli that are perceived as rather masculine (e.g., rotating box figures). When feminine stimuli are used, Ruthsatz et al. reported sex differences disappear. The degree to which a testing environment is more masculine may also play a role, as Ortner and Sieverding (2008) report that priming subjects with stories of a person who is “a self-confident and tough-minded person, who drives a motorbike” tends to reduce sex differences in mental rotation ability. Hooven et al. (2004) found sex differences in the confidence of judgments was a key factor in the observed sex differences in mental rotation ability. Coutrot et al. (2018) found men were better than women in spatial ability based on a web app used by more than 2.5 million people around the world, finding sex differences were related negatively to the gender inequality of their country. Clearly, the gendered nature of testing environments can affect the size and nature of sex differences in cognition, as do many other mediating factors (Eals & Silverman, 1994). As such, there may be important boundary conditions for the explanatory power of these evolved sex differences in mental abilities. Other factors matter a lot.
Another boundary condition is whether mental rotation is tested using purely visual mental imagery ability versus also involving tactile sensations and fine motor abilities (i.e., haptic rotation). Fisher and her colleagues (2017) found sex differences were eliminated in a study in which men and women could manually touch and rotate actual three-dimensional figures (either seeing or blindfolded). However, even if we assume a relatively large mental rotation effect size of d = +0.80 (much larger than most observed sex differences in mental rotation), they needed at least 25 men and 25 women in each condition for sufficient power. They did not have that. For instance, they had 19 women and 21 men in the blindfold touch condition, and they had 17 women and 18 men in the seeing touch condition. Also in the touch experiment where Fisher and colleagues remarkably found no sex differences, almost everyone scored a near perfect score in both the blindfold and touch conditions (>90% correct; meaning, it was a really easy test and could not discriminate effectively among different mental rotation ability levels). Finally, physically rotating actual objects is not a pure test of mental rotation ability. It involves fine motor skills and haptic ability and is known to involve different mental rotation ability systems than visual tests ("most studies find there are independent systems for visual and haptic representations;" Shioiri et al., 2011). Fine motor skills are something women are better at than men (in that they have smaller fingers, Peters et al., 1990), although interestingly this advantage may be lowest at exactly the same time across the ovulatory cycle that women's mental rotation abilities are their highest (Hampson, 1990). So overall, this boundary condition relied on methods that were highly underpowered, lacked the ability to discriminate high and low performers, and wasn't really a pure test of visual "mental rotation" ability systems (which is they key ability of interest to those trying to explain sex differences in high level math test performance).
Still, some research findings seem to directly refute the Hunter-Gatherer Theory of sex differences in navigation and spatial abilities. For instance, Hoffman et al. (2011) found sex differences in a puzzle test were absent in a matrilineal culture (i.e., the Khasi) where property is inherited by the youngest daughter and men are not allowed to own land. However, Bailey et al. (2012) pointed out several problems with that study, including the fact the puzzle used by Hoffman et al. is similar to the Object Assembly subtest of the Wechsler Adult Intelligence Scale, which shows extremely small sex differences (d = +0.10), at least 10-fold smaller than those found for typical mental rotation measures. Bailey et al. also noted that by not including a control cognitive test it is impossible to rule out critical confounds in their findings, and that the Khasi are not as gender egalitarian as most Northern European cultures, within which psychologists have found the largest spatial ability sex differences in the world.
Each of the converging lines of evidence noted above is just a piece of evidentiary puzzle of human adaptation (Schmitt & Pilcher, 2001). Each data source has limits, and new evidence is always emerging that may sway sexual scientists on this issue. For instance, a recent study was heralded around the world as ground-breaking research that proves there are no sex differences in cognition (especially no sex differences in mental rotation ability; Toth & Campbell, 2019). This study was based on a sample of merely 32 men and 38 women.
At present, the vast nomological network of evidence for sex differences in navigation and spatial abilities stands in stark contrast to peculiar studies that appear at odds with this probable set of human adaptations. A fair overview of the evidence, as noted above and given proper caveats, leads to the conclusion that men and women tend to use slightly different navigation strategies and have moderately different spatial abilities.
Conclusions
According to the Hunter-Gatherer Theory of sex differences in navigation and spatial abilities (Silverman & Eals, 1992), gendered divisions of labor in our ancestral foraging past may have led to sex differences in spatial abilities related to navigation. Men were much more likely than women to hunt large animals over great unfamiliar distances in ancestral foraging cultures. As a result, men may have evolved spatial abilities for thinking about the world in Euclidian terms. In contrast, women in our ancestral past were primarily involved with gathering immobile food sources within familiar territory, which likely required superior spatial location abilities and thinking about the world in terms of landmarks.
We’ve evaluated 10 converging lines of evidence confirming:
1) men and women tend to use slightly different navigation strategies, and that several navigation-related spatial abilities, such as mental rotation ability and object location memory show very similar patterns of sexual differentiation,
2) many of these sex differences have been confirmed using meta-analytic techniques,
3) many of these sex differences appear to be pan-culturally universal in very large international studies (and, moreover, the size of the sex difference are typically largest in the most gender egalitarian nations of Northern Europe, so patriarchy and intense gender-role socialization are unlikely sources of psychological sex differences),
4) sex differences in spatial abilities have been documented in foraging cultures,
5) sex differences in spatial abilities have been found in studies of real-world behavior (e.g., car parking),
6) sex differences in spatial abilities have been found across numerous laboratory experiments (e.g., constructing IKEA furniture),
7) sex differences in spatial abilities appear to emerge very early in life (as young as 5 months!), suggesting there are organizational effects of hormone exposure in utero that give rise to at least some sex differences,
8) sex differences in spatial abilities appear related to sex hormone levels, including variations across the menstrual cycle and due to experimental manipulations, and studies looking at the organizational effects of testosterone exposure in the womb and at men’s and women’s different brain structure and activation patterns point to biological origins of cognitive sex differences,
9) sex differences in spatial abilities appear supported by so-called “natural experiment” studies of opposite-sex twins, sexual orientations, transsexuality, and CAIS,
and 10) what we know about non-human animals, in the wild and in the lab, supports the view that sexual selection can and does sculpt sex differences in navigation and spatial abilities.
Now, where was that Starbucks again?
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