Science has few more controversial topics than human intelligence-in particular, whether variations in it are a result of nature or nurture, and especially whether such variations differ between the sexes. The mines in this field can blow up an entire career, as Larry Summers found out in 2005 when he spoke of the hypothesis that the mathematical aptitude needed for physics and engineering, as well as for maths itself, is innately rarer in women than in men. He resigned as president of Harvard University shortly afterwards.

It is bold, therefore, of Jonathan Wai, Martha Putallaz and Matthew Makel, of Duke University in North Carolina, to enter the fray with a paper that addresses both questions. In this paper, just published in Current Directions in Psychological Science, they describe how they sifted through nearly three decades of standardised tests administered to American high-school students to see what had been happening to the country’s brightest sparks.

They draw two conclusions. One is that a phenomenon called the Flynn effect (which weighs on the ‘nurture