Newly published research could fuel the fiery debate over whether one gender is innately more intelligent than the other - a controversy that already has featured the resignation of a Harvard president and an academic battle in Denmark. The latest study from Canada reports that 17- to 18-year-old males have a slight edge in IQ, based on an analysis of more than 100,000 SAT scores. But even the researcher behind the study acknowledges that the findings don't represent the final word on gender and intelligence.
Psychologist J. Philippe Rushton of the University of Western Ontario says the research was prompted by earlier studies in Britain and Denmark that reported a 4- to 5-point IQ advantage for men, based on assessments of general intelligence. "My colleague, Douglas Jackson, and I decided that we really needed to confirm [the findings of] these other two psychologists, and we confirmed them," he said.
Past studies have tended to declare the gender intelligence contest a virtual tie, with men rating higher in spatial ability (for example, reading a map) and women having an edge in verbal ability (using a varied vocabulary).
In their analysis, Rushton and Jackson interpreted the SAT results from both the math test (where males do better) and the verbal test (where females do better), focusing on 145 questions that seemed to emphasize general intelligence - also known as the "g factor."
"The g factor really is the active ingredient, if you will, that permeates all types of intelligence," Rushton told me.
Rushton cites an easy example of the difference between a low-g and a high-g task. First, think of the last four digits of your phone number. That's low-g. Now, think of them in reverse order. That's high-g. "It is a real cognitive load for everybody," Rushton said.
Unfortunately, Jackson passed away before the results could be published, but Rushton finished the work - and the study now appears in the September issue of the journal Intelligence. Based on their measurement of the g factor, they found that males had an IQ advantage of 3.63 points in the 17-to-18 age group.
That male advantage was found "throughout the entire distribution of scores, in every level of family income, for every level of fathers' and of mothers' education, and for each and every one of seven ethnic groups," Rushton said in a university news release.
In the paper, which is available online, the researchers suggest the advantage is due to "extra male neurons" in a guy's brain, which is on average larger than the female brain. (Other researchers have questioned whether size really matters when it comes to intelligence.)
Now, there are questions galore about this type of research. I'll start with the ones that Rushton addressed in my interview:
- Don't women get better grades than men in college? "Women do do better, in many but not all grades," Rushton replied. "And that's not just in college, but even in high school. Obviously, there are other things going on besides general intelligence. The one big factor that women have is conscientiousness." Rushton said "women will always do better" in an environment that emphasizes continual assessment (such as a quarter's worth of coursework) rather than one big effort (such as a final exam or project).
- Don't girls generally start out smarter than boys? Rushton acknowledges that in the early teens, females tend to have higher IQs than males. "We think it's because females mature faster ... so this masks the cognitive development," he said. In his view, it's a biological fact that males catch up and surpass the females as they mature.
- Isn't society to blame, for pressuring girls to "dumb themselves down" as they mature? "We're not really saying whether this is a genetic or an environmental factor," Rushton said. "We think it's probably both, but the fact that it shows up on the g factor rather than on specific types of items, inclines against that view" of society putting pressure on girls.
- Are SAT scores and the g factor really the proper ways to measure intelligence? What is intelligence, anyway? These are questions that cast a pall over all sorts of comparative intelligence studies, due to the controversy surrounding SAT tests as well as the g factor. Rushton says that measures of general intelligence are, if anything, more reliable than test scores - and he claims that the military uses such measures to predict how well recruits will perform tasks ranging from combat operations to potato-peeling. "What the psychologists have found there, is that it's the g factor that predicts all the different criteria they could want to predict," he said.
Science writer Deborah Blum, who surveyed decades' worth of research on gender and intelligence in her book "Sex on the Brain," raised bigger questions about the whole idea of pitting men against women in a showdown over average IQ.
"I would take any study that averaged results with an enormous grain of salt," she said. Males tend to show more variability than females in intelligence tests, which could skew the broader statistical results in favor of the males, she said.
Blum does believe, however, that there are differences between male and female brains - a view that has received some high-profile media exposure, thanks to recent research and a hot-button book titled "The Female Brain." She goes along with the "spatial/verbal" gender split, for example.
"Everything that I have seen that looks at the basic development of spatial reasoning suggests that there's an evolutionary advantage for the men," she said. The idea is that males came to specialize in the spatial skills needed to be successful hunter-gatherers.
The same rationale could apply to females' verbal advantage: "There are evolutionary reasons for that, having to do with child rearing as much as anything else," Blum said.
Blum's bottom line, however, is that it's not useful to engage in a sexual war over intelligence.
"It makes sense to say it's one big spectrum," she said. "It's all individual variability in the end. I think we're fooling ourselves to say we have identical brains. We don't. ... I get really tired of people telling me that."
So what do you think? Is it scientifically incorrect to talk about sexual differences in intelligence, or just politically incorrect? Feel free to weigh in with your comments.