Are the dots on this graph evenly spread out? Nope. They kinda cluster along a line that starts in the lower left and goes to the upper right. That’s one of the reasons why researchers Janet Hyde and Janet Mertz of the University of Wisconsin concluded in the Proceedings of the National Academy of Sciences that:

… gender inequality… is the primary reason fewer females than males are identified as excelling in mathematics at the highest levels in most countries.

The higher a country’s dot is on the graph, the more equal the genders are in that country’s culture (according to the World Economic Forum’s Gender Gap Index). The farther to the right a country’s dot is, the more girls it has on its International Math Olympiad teams. So the fact that the dots are not spread out evenly means that there’s some correlation between culture and math ability/participation. Perhaps more significantly, the researchers found no correlation between the number of girls on a math them and that team’s ranking. If gifted girls are inferior to gifted boys, you’d expect teams with more girls to rank lower. Hyde & Mertz conclude that together, these facts are a strike against older theories about biology’s link to math ability.

Hyde and Mertz explain the history:

Researchers first began investigating gender difference in abilities and behaviors in the 1880s. The scientists of the time concluded that women’s brains were sadly deficient.

Over the past few decades the math ability gap between average boys and girls has been narrowing to the point that:

U.S. girls have now reached parity with boys, even in high school, and even for measures requiring complex problem solving.

What’s been more controversial is whether there are more males that females among the very smartest. Historically, there’s been a theory that even if males and females are equally good at math on average, male ability is more variable, resulting in more of the top-tier (and bottom-tier) being male. That could explain why more elite scientists and mathematicians are male. However in recent years, studies of variability have given conflicting results that depend on ethnicity and country. After examining such studies, the authors conclude:

Given the absence of universality, the occurrence of greater male variability… must be largely due to changeable socio-cultural factors, not immutable, innate biological differences between the sexes.

Moreover, the researchers point out that in the U.S., the gender gap in tests of “mathematically precocious” youth has narrowed dramatically, coincident with the enactment of Title IX, and with increased immigration. There’s much yet to consider:

Of course, gender inequity is complex and multifaceted. It can encompass dynamics in school classrooms leading teachers to provide more attention to boys; guidance counselors, biased by stereotypes, advising females against taking engineering courses; mathematically gifted girls not being identified and nurtured; scarcity of women role models in math-intensive careers leading girls to believe they do not belong in them; unconscious bias against females in hiring decisions; and hostile work environments leading qualified women to drop out in favor of friendlier climes.

Let’s hope that increasing evidence pushing biology out of the picture will encourage more focus on these socio-cultural issues.