A study of 130 newborns found that girls spent a larger proportion of their viewing time looking at human faces than boys, suggesting that sex-related differences in attention may be present within hours of birth. Researchers said this could indicate a role for prenatal biological factors, while stressing that development is shaped by both nature and nurture.

The babies, all tested within 72 hours of birth, watched videos of a face and a Newton’s cradle while researchers recorded their gaze without knowing the infants’ sex or which stimulus they viewed. Both sexes generally preferred faces, but the difference appeared only as an average between groups and does not mean every girl will be more attentive than every boy; the team also cautioned that the study did not directly identify biological causes.