The debate surrounding sex-based differences in intelligence has long divided both experts and public opinion. Historically, claims of a male superiority in intelligence have been used to reinforce negative gender roles and stereotypes. Nevertheless, understanding any relationship between sex and cognitive capabilities is an important dimension in the understanding of intelligence as a whole, supporting research and interventions that can benefit all individuals, regardless of sex. This essay seeks to explore the varying evidence regarding sex differences in intelligence, critically evaluating the validity of associated explanations. First, this essay will outline current evidence of sex differences with regards to general intelligence (g), as well as the more robust evidence concerning sex differences within specific domains of intelligence. These will serve as the basis for critically evaluating the role of both biological and sociocultural explanations for such disparities. It should be noted that division of these two interrelated factors serves as an organisational measure, rather than suggesting any mutual exclusivity.

            Mixed evidence surrounds the debate of sex differences in g. Some argue for a male superiority, with meta-analyses indicating male advantages of roughly 3-5 IQ points (e.g., Lynn, 1994; Jackson & Rushton, 2006; Nyborg, 2005). Others have found trivial or non-existent differences (e.g., Aluja-Fabregat et al., 2000; van der Sluis et al., 2008). The latter position often asserts that reported sex differences in g are artefacts of the specific test batteries used, and that assertions of a male superiority neglect gene-environment interactions. Notably, a meta-analysis commissioned by the American Psychological Association has endorsed this second position (Neisser et al., 1996), which has been reaffirmed in a more recent review (Nisbett et al, 2012).

            Given the diversity in results regarding sex differences in g, there is a growing focus on differences in specific cognitive abilities. Meta-analyses have robustly demonstrated the tendency of females to score higher on tests involving verbal cognitions (e.g., Hirnstein et al, 2023; Barel & Tzichinsky, 2018) and of males to score higher on tests involving visuo-spatial cognitions (e.g., Uttal et al., 2013; Nazareth et al., 2019).

            Theories seeking to explain these results have often leaned on biological disparities between the sexes. Early hypotheses noted a correlation between IQ and brain volume of around .40, positing that larger brain sizes in males accounted for the male superiority in g (e.g., Filipek et al., 1994; Lynn 1994). However, given the mixed evidence regarding sex differences in g, newer theories suggest that neuroanatomical differences contribute to the diverse cognitive profiles between the sexes, but not to any inherent general superiority.

            For example, in the largest single-sample study to date, it was found that while males tend to have larger brain sizes, more cortical surface areas, and more white matter diffusion directionality, features associated with intelligence, females tend to have thicker cortices and higher white matter tract complexity, also associated with intelligence (Ritchie et al., 2018). Similarly, while males tend to have larger grey-matter volumes in the amygdala, hippocampi, and temporal areas, females tend to have larger volumes in the right frontal area, thalami, and portions of the parahippocampus and occipital cortex, (Giedd et al., 1997; Ruigrok et al., 2014). These neuroanatomical differences between the sexes likely explain the observed differences in specific cognitive abilities between sexes, as well as the lack of robust evidence towards the unequivocal g superiority of either.

            Some contend that variations in sex hormones contribute to sex differences in intelligence. For example, increased prenatal exposure to androgens (male sex hormones such as testosterone) has been shown to mediate the development of spatial abilities by promoting the development of right hemisphere dominance, a region heavily implicated in spatial cognitions (Berenbaum et al., 2005; Vogel et al., 2003). Females with congenital adrenal hyperplasia (CAH), characterised by elevated prenatal androgen levels, exhibit cognitive profiles more akin to males, displaying superior performance in visual-spatial tasks compared  to control females (Puts et al., 2008). The Twin Testosterone Transfer hypothesis, premised on higher androgen transfer between foetuses, has shown that females with fraternal male twins and as such, elevated prenatal androgen exposure, exhibit superior performance in spatial cognition tasks (Tapp et al., 2018) with subsequent reviews reaffirming the robustness of these findings (Ahrenfeldt et al., 2020). The relationship between androgens and spatial abilities suggests how differing hormone levels between genders may influence their  cognitive differences.

            However, the influence of socio-cultural factors on sex differences in intelligence complicates any direct causal interpretations due to biology. Take for instance, the evidence suggesting that males tend to have better spatial cognitive abilities. Kotsopoulos (2021) demonstrated, not only that early engagement with related activities (e.g., puzzles, blocks, board games) enhances associated cognitive abilities, but also that young boys engage much more frequently in such activities, even when controlling for cognitive ability. This latter finding suggests that boys’ preference for visuo-spatial skill related toys is not solely due to inherent cognitive capacities. The role of sociocultural influences in this preference is visible when considering established distinctions in gender patterns of values and interests, as well as children’s tendency to prefer activities associated with their own sex (Su et al., 2009; Martin et al., 2013). This socio-cultural division self-perpetuates, and studies have noted that females feel less inclined towards traditional male interests and careers due to the lack of female representation and societal expectations (Frenzel et al., 2007). Cultural values ingrained from an early age shape engagement with specific cognitive activities, ultimately influencing cognitive capacities and eliciting the observed sex differences in various intelligences. Notably, research suggesting male IQ superiority has often overlooked the role of cultural values and unequal educational opportunities, emphasising inherent biological explanations (Lynn, 1994, 2002).

            The testing instruments used to measure intelligence likely reflect these socio-cultural divisions. For example, the Wechsler Adult Intelligence Scale (WAIS) is recognised as a robust and valid indicator of ‘intelligence’. However, the ‘General Information’ subtest of the WAIS, in which females tend to score lower than males, includes questions such as ‘What is the chemical symbol for water?’ or, ‘What is the largest continent by land area?’ (Rammstedt et al., 2002). Intuitively, higher male scores in this subtest does not reflect greater intelligence, just broader trends in values and interests. Clearly, metrics of general intelligence may be determined by sociocultural dynamics rather than inherent cognitive abilities.

            Unconscious sociocultural influences may also confound measurements of sex differences in intelligence. Stereotype threat, in which individuals from stereotyped groups underperform due to negative stereotypes about their cognitive abilities, has been observed in studies looking at gender (Steele & Aaronson, 1995; Steele, 1997). In a meta-study involving 224 effect sizes across 86 separate studies of female stereotype threat on math and spatial cognition, finding a small, but significant effect (Doyle & Voyer, 2016; Flore & Wicherts, 2015). As such, subtests on traditional intelligence metrics involving traditionally ‘male’ cognitions may reinforce male superiorities, not through greater cognitive ability, but through the negative consequences of stereotype threat, although the impact of such a complex phenomenon is unclear.

            That being said, evidence from more gender-equal countries challenges the extent to which sociocultural factors determine sex differences in cognitive abilities. One might expect that in nations with greater gender parity, such differences would diminish due to the reduced impact from differing sociocultural influences. Yet, while disparities in education-related cognitions (e.g., maths) have decreased (Guiso et al., 2008), differences in more fundamental cognitive abilities (e.g., verbal, spatial) have actually become more pronounced (Lippa et al., 2010). Moreover, despite significant advancements in female education and opportunities since the 1970s, the number of women entering high-status professions has surged, but the proportion of women in traditionally male fields (e.g., STEM,  mechanics) has remained low and relatively stable (Lippa et al., 2014). Clearly, sociocultural reasons cannot fully account for observed sex differences in cognitive abilities. Given the evidence from both biological and sociocultural standpoints, it is likely that any inherent sex differences in cognition (the extent of which is unclear) are amplified over time through differential experiences shaped by sex-specific sociocultural values. This would explain why such differences remain in countries with less distinct sociocultural divisions between the sexes.

            In conclusion, any conclusions regarding the superior general intelligence of either sex should be treated with significant caution. Standard metrics of intelligence are of best use in assessing specific cognitive abilities and in a clinical context, facilitating the care and treatment of particular individual, rather than being the basis for any broad conclusions regarding cognitive abilities between the sexes. That being said, there are clearly some differences within specific sub-domains of intelligence, the reasons for which are convoluted and complexly interrelated. Neuroanatomical and hormonal differences between the sexes clearly shape cognitive abilities to some extent. However, it is currently unclear how the differing sociocultural contexts of males and females may moderate the manifestation of these differences. It appears that intelligence, like many human cognitions, is determined by a complex interplay between biological and environmental aspects. Given the diversity of empirical results and theoretical explanations, future studies would benefit from a biopsychosocial approach to understanding the mosaic of factors that shape intelligence, emphasising the reciprocal relationships among many types of variables, biological, sociocultural or otherwise.

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