Abstract
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 16years 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 16years 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.
Highlights
Females scored significantly higher than males on both verbal and non-verbal abilities at ages 2, 3 and 4
The findings indicate that the twin testosterone transfer effect occurs only for specific cognitive abilities, such as mental rotation
Research findings have traditionally indicated that sex differences favoring males appear in non-verbal abilities (e.g. Voyer, Voyer, & Bryden, 1995), while sex differences favoring females appear in verbal abilities (Hyde & Linn, 1988)
Summary
Research findings have traditionally indicated that sex differences favoring males appear in non-verbal abilities (e.g. Voyer, Voyer, & Bryden, 1995), while sex differences favoring females appear in verbal abilities (Hyde & Linn, 1988). Research findings have traditionally indicated that sex differences favoring males appear in non-verbal abilities Voyer, Voyer, & Bryden, 1995), while sex differences favoring females appear in verbal abilities (Hyde & Linn, 1988). Within verbal abilities males often do better on verbal analogies (Colom, Contreras, Arend, Leal, & Santacreu, 2004), whereas females outperform males on natural language competencies, reading and writing (Geary, 2010; Stoet & Geary, 2013). Non-verbal abilities refer to ‘the skill in representing, transforming, generating, and recalling symbolic, non-linguistic information’ (Linn & Petersen, 1985). Verbal abilities refer to measures of language usage, such as grammar, spelling, reading, writing, verbal analogies, vocabulary and oral comprehension (Halpern, 2000). We adopt these definitions for verbal and non-verbal skills for convenience
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