Sex differences in non-verbal and verbal abilities in childhood and adolescence

•Small sex differences in non-verbal and verbal abilities across development•Female advantage in both non-verbal and verbal abilities at ages 2, 3 and 4•Male advantage in verbal abilities at ages 10 and 12•Twin Testosterone Transfer Hypothesis: females with male co-twins outperformed same-sex female twins on mental rotation.•Results from this study showed no evidence for the Twin Testosterone Transfer Hypothesis on non-verbal or verbal abilities.

Twin research has shown that females with male co-twins perform better than females with female co-twins on mental rotation. This beneficial effect of having a male sibling on spatial ability could be due to in-uterine transmission of testosterone from males to females (the Twin Testosterone Transfer hypothesis, TTT). The present study explored sex differences and the TTT in non-verbal and verbal abilities in a large sample of twins assessed longitudinally at 2, 3, 4, 7, 9, 10, 12, 14 and 16 years of age. Females scored significantly higher than males on both verbal and non-verbal abilities at ages 2, 3 and 4. Males scored significantly higher than females on verbal ability at ages 10 and 12. The effect sizes of all differences were very small. No sex differences in non-verbal or verbal abilities were found at 7, 9, 14 and 16 years of age. No support for the TTT was found at any age. The findings indicate that the twin testosterone transfer effect occurs only for specific cognitive abilities, such as mental rotation.