The very definition of intelligence has been hotly debated in the scientific community as well as among the general public for centuries (Neisser, 1979). The way intelligence is defined varies massively between cultures, contexts, and individuals (Sternberg, 1981), yet for as long as this debate has continued, so has the question of which of the human sexes outsmarts the other — despite the lack of clarity as to what constitutes ‘outsmarting’. Biologist George Romanes’ 1887 article ‘Mental Differences Between Men and Women’ posited that, given women’s relatively smaller brains, we ‘should expect marked inferiority of intellectual power’ from them. Over a century later in 1992, Ankey and Rushton made the same prediction based on their finding that human male brains are indeed larger than females’. Whilst these examples appear to suggest consistent sex differences in intelligence, other literature in this area is far from consistent or conclusive (Nyborg, 2005). As mentioned, researchers disagree on how best to define and test intelligence; although countless studies are conducted in this field, they differ enormously in the type of intelligence they investigate and the way they measure it. Methodological flaws and researchers’ personal convictions, given this politically sensitive issue, also bring many papers under scrutiny. In response to the essay title, it appears there are sex differences in ability, but not intelligence. Intelligence, for the purpose of this essay, will be defined as the summative problem-solving power of an individual’s cognitive abilities, measured in ‘IQ’ or ‘g’ (which will in turn be defined and discussed later). Each sex outperforms the other in certain measures of intellect, but despite the deep implications of such a conclusion, evidence is anything but consistent.
Lynn’s 1994 study is one cited by many researchers who believe consistent sex differences in intelligence exist (e.g. Pakkenberg & Gundersen, 1998). Lynn found males have larger brains than females even when corrected for body size, and argued that, since brain size is correlated with intelligence, men should generally be more intelligent than women. He also found that males have higher verbal, reasoning, and spatial abilities than females, stating that this equates to males scoring four IQ points higher on average than women. Similarly, Brown and Brian (1955) found ‘sex differences…at all age levels favouring males on Verbal and Full Scale scores’. One theory as to why this might be the case relates to hormone exposure which each sex receives in the womb. Davis and D’Amato (2010) found adult women exposed to high levels of testosterone in the womb scored higher in tests of spatial ability, a skill in which males are usually superior, than other women. Silverman (2000) reasons that a male advantage in this domain is evolutionary advantageous: men, historically, spent more time hunting, gathering, and navigating than women. An evolved superiority in spatial ability may account for Lynn and Irwing’s (2004) meta-analysis finding that males score higher than females in Raven’s Progressive Matrices (a non-verbal reasoning test). Sex differences here escalated after puberty, consistent with the theory that testosterone enhances spatial ability. However, it seems illogical to conclude that males are intellectually superior because hormones enhance their performance in tests of one skill. Also, in a discipline constantly evolving and disproving its previous beliefs (Chambers, 2014), it is unusual that there is little research to dispute this finding. Factors such as publication bias and societal norms have likely prevented this (Eliot, 2019). Therefore, the research discussed does not necessarily indicate a consistent male intellectual advantage.
This becomes apparent when methodological errors in these studies are inspected. For example, studies used in Lynn and Irwing’s (2004) meta-analysis were hardly representative of any population they claimed to represent. Hunt (2010) exposed the following issues: one study from Israel, claiming to represent the entire country, was conducted on children in one kibbutz. A study representing USA college students used only 200 students from one university — the male:female ratio 9:2 despite the university’s equal gender ratio at the time. A study representing India, whose population exceeds one billion, contained only 200 participants, and a study in Brazil involved 1,900 men but only 740 women. None of these studies approach representation of any country. Lynn and Irwing do not mention this in their meta-analysis. Furthermore, John Raven (1989) found no sex differences in performance on Raven’s Progressive Matrices (a test he created, used by Lynn and Irwing). Lynn and Irwing’s erring from scientific standards suggests an ulterior motive — a possibility since Lynn is an ‘American Renaissance’ member. This organisation promotes ‘research’ highlighting the ‘superiority’ of white people (particularly males) to people of colour. This affiliation, alongside his questionable research quality, should suffice to discredit Lynn’s work. Brown and Brian’s (1955) paper, claiming to find sex differences in intelligence, is also problematic. Participants were high school and university students, students of each sex in 1950’s USA rarely receiving equal opportunities. Female students typically studied subjects such as home economics and textiles, males encouraged to pursue sciences and mathematics (Layman, 2001). Males’ schooling may explain their apparently higher intelligence test scores: they were more accustomed to this format of testing and way of reasoning, which was likely less familiar to female students. All this considered, consistent male intellectual prowess seems less probable, the opposite possibility yet to be explored.
When told that sex differences may exist in intelligence, many may assume this refers to a male advantage. Furnham and Rawles (1995) found participants estimated higher IQ scores for male than female family members, and for people in stereotypically ‘masculine’ professions (e.g. bricklayer) than ‘feminine’ professions (e.g. cleaner). However, some studies suggest the opposite: women may have an intellectual advantage over men. Terman (1916) found women were superior to men at comprehension tests of intelligence — measures described as ‘one of the best single indicators of overall intelligence’ (Sternberg & Powell, 1983). Terman also pointed out that women were perhaps perceived as less intelligent due to societal factors, remarking that: respected occupations ‘are only now opening their doors to women’, that a woman’s role in society was ‘largely that of home-making’, and that even working women ‘marry and thereafter devote their energy to childrearing’. Because of these factors, says Terman, ‘women are not inspired by deep-seated motives to constant intellectual endeavour as men are’. In short, the sexes were not given equal opportunities for mental growth, resulting in inaccurate assumptions of intellectual discrepancies. Despite this, women still show superiority in some tests. A century after Terman suggested women, given identical privileges, would achieve as highly as men, Voyer and Voyer (2014) found women outperform men in academia: in primary, secondary, and tertiary education. Perhaps this is what led Eagly (2019) to find that perceptions of women’s intelligence have changed dramatically since the 1940’s, over which time female school absence has diminished (Roser, 2015). Eagly found that in 1946, 35% of responders saw the sexes as equally intelligent, whereas now 86% believe this is the case — 9% perceiving women as more intelligent. The research examined here implies sex differences in intelligence, but it is not consistent with many previous studies. Perhaps we fail to see consistent differences because our society and norms are constantly changing.
Or maybe we fail to see consistent differences because there are no significant differences to be found. Men and women outperform each other in particular abilities, but intelligence is an amalgamation of these abilities (Garai & Scheinfeld, 1968). These may present and interact differently between the sexes, resulting in a negligible or non-existent intellectual difference. Haier (2005) found exactly this: males and females achieved similar IQ scores using different brain areas. In males, IQ score correlated with frontal and parietal lobe activity, while in females it correlated with frontal lobe and Broca’s area activity. The cognitive strengths of each sex are represented by this distinct brain activity: the parietal lobe is associated with spatial and mathematical ability, while Broca’s area is responsible for language production and comprehension (Hines, 2018). This is consistent with Halpern and LaMay’s (2000) finding of males’ ‘superior ability to manipulate visual images in working memory’, and female prowess in ‘tasks requiring retrieval from long-term memory and the acquisition and use of verbal information’. This may account for the discussed female advantage in academia, a field in which success depends more on language and long-term memory skills than spatial ability (Eisenberg, 2005). Colom’s (2000) study, similarly to Haier’s, tested males and females on a variety of abilities then used these scores to generate a score in g (g, theorised by Charles Spearman in 1904, is a measure of ‘general intelligence’, aiming to reflect one’s ‘deeper mental energy’). Colom found negligible sex differences in g, supporting the above hypothesis that the different abilities of each sex amount to similar if not equal scores of general intelligence (measured either as IQ or g). This considered, and as mentioned in the introduction, perhaps the discussed sex differences in ability have been repeatedly mistaken for sex differences in intelligence.
The implications of the claim ‘there are consistent sex differences in intelligence’ are many and profound. Firstly, the very idea that one sex is intellectually superior has clearly aroused enough competition to warrant hundreds of studies into the matter, each concluding something slightly different. The media interpret these studies how they will, often exaggerating and / or misinterpreting findings. For example, Metro published an article titled ‘Men ‘have bigger brains than women’ (and that’s why men have higher IQs)’ (Waugh, 2017), citing ‘sources’ such as the Daily Mail. Laymen read and interpret such articles how they will, until the general public is convinced of the superiority or inferiority of their sex — neither outcome healthy or justified. Articles such as Metro’s may be the cause of Cooper’s (2018) finding that male university students perceived themselves more intelligent than female peers, even when shown said peers’ grades — which often suggested otherwise. Furnham and Buchanan (2005) found women estimated lower IQ scores for themselves than men did, suggesting perceptions of male intellectual superiority occur in both sexes. If women are viewed both by men and other women as less intelligent than men, this could legitimise workplace sexism. Holleran (2011) found that even in prestigious workplaces with highly-qualified employees, both sexes were less likely to discuss research with female colleagues, and when research was discussed, female colleagues were rated as less competent than males. As Fine (2011) suggests, this could all be the result of ‘stereotype threat’, a phenomenon in which stereotyped individuals perform worse in tasks than the non-stereotyped. In this case, women, stereotyped as intellectually inferior (due to factors discussed), may perform less competently at work because this is expected of them. All the consequences discussed here can be traced back to the claim that there are sex differences in intelligence.
In conclusion, the claim that there are consistent sex differences in intelligence is unfounded. While research such as Lynn and Irwing’s (2004) and Brown and Bryan’s (1955) studies may give casual readers the impression that intellectual differences exist, basic scrutiny of these papers and their authors exposes myriad flaws. Any amount of further reading into this matter (beyond distorted tabloid articles) will also raise skepticism, and considering factors which may have lead to perceived differences (such as unequal opportunities and stereotype threat) illuminates the true state of affairs: that there are no consistent sex differences in intelligence. Studies claiming to have found such discrepancies are, as discussed, most often misreporting. They have not found intelligence differences, but ability differences. As Haier (2005) found, the sexes may have distinct abilities, but these amount to equal IQ. The real-world implications of the claim in discussion, regardless of its accuracy, include unhealthy beliefs of one’s gender’s superiority or inferiority, casual (and seemingly legitimised) sexism, discrimination of resources and opportunities, and a vicious cycle of stereotype threat — women most often on the receiving end of all of these. The claim that there are consistent sex differences in intelligence is dangerous, damaging, and inaccurate.
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