Weekend Reads | Are There 'Sex Differences' in Intelligence? The Studies Are … Messy

by Kevin Schofield

This weekend's read revisits an age-old debate: Whether there are differences in intelligence between the genders. This and related questions have been argued for thousands of years, and while plenty of tests have been created to purportedly measure a person's intelligence (and compare it to others'), the issues of how to define, measure, and compare intelligence have only become more controversial and messy over time.

Any attempt to measure intelligence must begin by defining it. Scientists have been attempting to crisply define (and measure) "general intelligence" as far back as 1904, but nearly all who try to do so inevitably decide that it isn't its own thing but rather a combination of more specific mental abilities, such as memory, language processing, visual processing, and decision-making. In fact, much of the ongoing debate about intelligence regards what the lower-level mental abilities are, whether those parts are independent or related to each other in a "network" of cognitive skills, and whether they further decompose into smaller, more narrow skills.

The current consensus among researchers is that the more you generalize intelligence, the less differences there are between the sexes. Rather than a "gender differences" hypothesis, this has led them to declare a "Gender Similarities Hypothesis": that men and women are similar on most psychological variables, including general intelligence. However, there are a handful of narrower mental abilities that testing has consistently shown to advantage men or women — though mostly by small amounts. And this weekend's read, a research paper by a trio of professors at the University of Kansas, Texas A&M University, and the University of Connecticut, tries to dissect out some of those narrower differences underlying general intelligence.

For example, women appear to be better at "processing speed": In aggregate, they can accomplish cognitive tasks slightly faster than men. But the tests used to determine that require speed, accuracy, and fine motor skills, suggesting that we need to keep digging down to uncover where the real differences lie. Doing so, researchers have found that women are better at perception speed, reading speed, and writing speed, but not mathematical speed. At the same time, men seem to have the advantage in movement time, broad reaction time, and decision speed.

With regard to visual processing, men appear to have a slight advantage in visual processing speed, spatial orientation, mental rotation, and remembering "non-nameable" images and routes, whereas women are better at tasks requiring remembering object locations. This feels like the perfect setup for jokes about men and women driving, and men who can't find their car keys.

There don't appear to be gender differences in long-term memory abilities, at least at a high level, though tests have found that women are better at some tasks involved in learning new information efficiently.

The authors report that writing is the "largest and most consistent sex difference" in mental abilities. Women show a consistent advantage over men, one that increases as the writing task becomes more complex. But math is the flip side of that, sort-of: There are more men who are high achievers at math problem-solving than women (though there are equal numbers of low achievers). Similarly, the findings for reading ability are also mixed: Women have an advantage in reading fluency, where the bottom 20% of men do worse than the bottom 20% of women. All three of these findings seem like good cases for further drilling down to understand if there are narrower skills that cause the differences.

There are many issues with this kind of research. As the authors point out, interpreting this kind of data often leads us to "broad interpretation of a narrow test," in which we read too much meaning into a very confined result. And as mentioned earlier, we need to wrestle with whether a particular mental ability we are testing for stands alone, correlates with other abilities (suggesting an underlying connection), or can be further broken down into even smaller tasks that reflect narrower abilities.

And, of course, intelligence tests have been shown to harbor all kinds of biases: racial, cultural, educational, gender, and more. Does a test measure what someone has learned previously, or an innate ability? Does it reflect their vocabulary (both the words in the test, and the words used in the instructions)? Does practicing an intelligence test lead to a better score, and if so, does that reflect improved mental ability or simply more familiarity with the test?

And we can't forget that our entire understanding of gender has evolved beyond thinking of it as a binary notion of either "male" or "female." Scientists have shown that the physical attributes that we have traditionally associated with "male" or "female" are not driven solely by the "X" and "Y" chromosomes; there are other locations in our genome that are involved. So just as we need to decompose mental abilities into their component parts, ultimately we need to decompose the notion of gender further before drawing broad conclusions about sex-related genetic advantages in intelligence. The authors limited their discussion to biological sex and gender assigned at birth (because they were surveying prior research that adopted that approach), but they did point to an example of research taking a broader look at gender-role differences — and finding that some of the observed differences in mental abilities may correlate better to gender role than to biological sex.

The authors declined to speculate on why or how the documented differences came to be: whether they are genetic traits that were selected for based on historical differences in societal gender roles, whether they have environmental roots, or whether we simply haven't decomposed them enough to discover the underlying differences. It's difficult to believe that skills such as math and writing that are relatively new, from the perspective of millions of years of human evolution, have already developed male/female differences; there must be something deeper driving the differences that we simply haven't uncovered yet.

The sexes do not differ in general intelligence, but they do in some specifics

Featured image via ivector/Shutterstock.com.