Levels of testosterone in the womb may have profound effects on a person’s social development. The findings might also explain why men are four times as likely as women to suffer from autism.

The team has already found that the babies with higher fetal testosterone levels had a smaller vocabulary and made eye contact less often when they were a year old. And a study by another group has shown that eight-year-old girls who had high fetal levels of the hormone performed better at tasks such as mentally rotating a two-dimensional figure.