The debate of which is the more intelligent sex has remained controversial. Although there is no difference in general intelligence between males and females, sex differences in higher cognitive abilities are frequently observed in scientific research (Halpern & LaMay, 2000). Male advantage in spatial ability is consistently found in small to medium effect size, and the cognitive ability is considered to be crucial for the development of quantitative reasoning within the field of science, technology, engineering and mathematics (STEM) (Reilly & Neumann, 2013). Whereas in mathematical ability, the effect size is relatively small with a considerable variability (Else-Quest, Hyde & Linn, 2010). Evidences suggested that the difference between sexes in spatial and mathematical performances could be influenced by both biological and environmental factors, and to a large extent it could be explained by both factors in a psychobiosocial approach over a pure nature-nurture debate.
In a psychobiosocial perspective, it is hard to draw a fine line between biological and environmental factors. For example, life experiences could drive synaptic pruning and then lead to changes in brain structures. For this reason, although sex differences in spatial and mathematical performance is somehow biologically programmed, the ability could be altered by environmental factors (Halpern & LaMay, 2000).
According to the evolutionary explanation, spatial abilities are qualitatively different between the two sexes. As seen in many polygynous species, males tend to travel longer distances in order to mate with more females, particularly during breeding seasons, in order to maximise their reproductive success (Jones, Braithwaite & Healy, 2003). Contrastingly, females are less likely to be engaged in high risks activities during reproductive periods (Sherry & Hampson, 1997), for example, long distance travel, in exchange for greater chance of survival for both herself and her offspring. As the primary caregiver of the offspring, females tend to be more concerned about survival, and thus are attentive more to spatial cues and landmarks in the immediate environment (Ecuyer-Dab & Robert, 2004), which is useful in retreating and avoiding enemies. Specifically in human primitive times, men performed as hunters and female performed as plant food gatherers, which demonstrate different spatial abilities. Mental rotation and orientation-based navigation are essential for hunting activities, where locating and understanding the relation of objects in the environment is essential for plant gathering. In support of the evolutionary theory, men significantly outperformed women on three-dimensional mental rotation tasks, and women scored significantly higher than males in object location memory tasks (Silverman, Choi & Peters, 2007). It is noteworthy that the results were found across 7 ethnicity groups, which suggested that there is a genetic basis in sex differences of spatial performance.
Males and females tend to adapt different strategies according to their difference in specialities when solving spatial task. Males were found to favour orientation strategy that is based on Euclidian descriptions, such as distance and cardinal direction, whereas women favour response strategy that uses relative environmental descriptions, such as landmarks (Rahman, Andersson & Govier, 2005). Orientation strategy requires more spatial knowledge compared to response strategy, and Halpern and LaMay (2000) argued that the use of visual-spatial strategy could enhance mathematical learning. Except for functional difference, Packard and McGaugh (1996) also suggested that the two strategies are mediated by different neural system. While the orientation strategy relies on the hippocampus, the response strategy relies on the activation of dorsal striatum. It is possible that sex differences in spatial tasks solving is due to different efficiency of the two neural systems, as there is no place cell firing or spatial foundation in striatum processing but only in hippocampal processing (Berke, Breck & Eichenbaum, 2009). In other word, the orientation strategy should be faster and more direct compared to response strategy, which is consistent to superiority of spatial tasks performance in males.
However, it is noteworthy that strategy preferences are not shown prior puberty (Kanit et al., 2000), suggesting that spatial ability differences emerges along with sex steroids activation during puberty. While increased oestrogen level is negatively associated with spatial performance, a positive relationship has been found between testosterone and three-dimensional mental rotation (Silverman, Kastuk, Choi & Philips, 1999). This suggested that activation of sex steroids could contribute to the difference in spatial task solving methods between men and women. Spritzer et al. (2013) have supported this hormonal hypothesis, and found that change in concentration of testosterone could shift strategic preferences in male rats. As well as in women, polycystic ovarian syndrome (PCOS) patients with elevated level of testosterone were found to perform significantly better than healthy women in mental rotation tasks (Barry, Parekh & Hardiman, 2013). The within individual test result in the PCOS study have again demonstrated the role of hormones in spatial task and the relevant performance difference between the two sexes.
Although there are biological evidences supporting sex differences in spatial ability, it is not possible to accept it as the sole explanation. Hoffman, Gneezy and List (2011) compared two culturally different but genetically related Northeast Indian tribes, and found that only women from the patrilineal tribe took longer time in puzzle solving task. Performance of men and women in the matrilineal tribe was insignificant, which suggested that spatial ability is not solely dependent on biological differences. In a larger scale study, although sex differences in mental rotation and line angle judgements were still observed across 53 nations, better performance in both visual-spatial tasks were positively associated with gender equality and economic development (Lippa, Collaer & Peters, 2010). It is possible that the promotion of gender equality reduces gender stereotype and bias, which could discourage female in performing masculine tasks. In the fields of STEM, faculties tend to favour males over females even when applications are identical (Moss-Racusin, Dovidio, Brescoll, Graham & Handelsman, 2012), indicating that the stereotype would limit the opportunity females have in developing spatial and mathematical skills. Spencer, Steele & Quinn (1999) also suggested that stereotype threat could weaken female mathematics performance when they believed males had advantage over females. Thus, gender stereotyping could be one of the factors that enlarged the sex differences in spatial and mathematical performances.
Gender role is acquired through many ways alongside with development. Reilly & Neumann (2013) suggested that masculine activities require more spatial skills than feminine activities, and Doyle, Voyer and Cherney (2012) suggested that childhood spatial activities were positively correlated with spatial and mathematics performances in adults. From this direction, it is possible that difference in spatial and mathematical ability is affected by different experience of childhood activities between boys and girls. Interestingly, children are not entirely passive in demonstrating gender-based preferences. Children tend to prefer toys that are stereotyped for their own sex, and find toys less attractive if they were labelled for the opposite sex (Martin, Eisenbud & Rose, 1995). While traditional masculine toys such as cars, guns and lego are more mechanical, traditional feminine toys, for example, Barbie and cooking games, emphasise on appearance and nurturing. Moreover, Cherney and London (2006) found that boys are more likely to be engaged in physically active sports and video gaming compared to girls, which require spatial skills such as hand-eye coordination and movement estimation. As boys are more exposed to spatial activities, it is possible that they have more opportunities in practicing spatial skills than girls. Thus, it is possible that the types of activity and environment exposed during childhood could contribute to the sex differences in spatial and mathematical abilities.
Other than childhood activities, social expectations from different stakeholders, such as parents, media and educator, could also influence sex differences in spatial and mathematical abilities. As the most important stakeholder in primary socialisation, parents are crucial in the development of children. Thus, stereotype in parents could have a heavy impact on cognitive skills development. Gunderson, Ranirez, Levine and Beilock (2011) suggested that parents have a tendency to believe that boys are naturally gifted in STEM related subjects, while the achievement of girls are mainly boosted by effort. What is more, Gunderson and colleagues also found that teachers tend to believe that boys are more capable in logical thinking and thus could master mathematics better than girls. This belief is reinforced when female teacher has high math anxiety, and is found to influence mathematical achievement of girls (Beilock, Gunderson, Ramirez & Levine, 2010). The reinforcement of these gender biases would therefore become self-fulfilled prophecy and to a more negative attitude towards mathematics and acts as a barrier for girls who are trying to develop their knowledge and career in STEM, or other male dominated fields. The portrayal of scientists in mass media is also found to discourage female participation when male superiority and dominance is promoted (Cheryan, Plaut, Handron & Hundson, 2013). From the evidences above, there is a reason to believe that the reinforcement of gender stereotype and social expectations leads to conformity, and enlarged the gap between the two sexes in the field of STEM.
To sum up with the psychobiosocial approach, it is not possible to separate biological and environmental factors when explaining sex differences in spatial and mathematical abilities. Either one can only contribute a small extent of explanation but both biological and environmental influences have to be integrated in order to explain sex differences in spatial ability to a large extent. Superiority of males in spatial and mathematical tasks could be a predisposition due to hormonal and evolutionary factors, which further facilitate skills development from relevant activities and thus result in greater achievement. The gap between two sexes could emerge when females do not benefit from such predisposition, receive less support and exposure opportunities in developing spatial and mathematical skills during socialisation.
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