Origins of handedness: A nationwide study of 30 161 adults

The origins of human handedness remain unknown. Genetic theories of handedness have received much attention, but some twin studies suggest modest, perhaps negligible genetic effects on handedness. A related question concerning handedness is whether twins have higher rates of left-handedness than do...

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Bibliographic Details
Published in:Neuropsychologia 2009-04, Vol.47 (5), p.1294-1301
Main Authors: Vuoksimaa, Eero, Koskenvuo, Markku, Rose, Richard J., Kaprio, Jaakko
Format: Article
Language:English
Subjects:
Adolescent
Adult
Age Factors
Aged
Ambidextrousness
Cohort Studies
Cross-Sectional Studies
Female
Forced-handedness
Functional Laterality - genetics
Genetic effects
Humans
Left-handedness
Male
Middle Aged
Models, Genetic
Sex Factors
Social Environment
Triplets - genetics
Twins
Twins - genetics
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Summary:The origins of human handedness remain unknown. Genetic theories of handedness have received much attention, but some twin studies suggest modest, perhaps negligible genetic effects on handedness. A related question concerning handedness is whether twins have higher rates of left-handedness than do singletons. We studied handedness, with information on forced right-handedness, in a sample of 30 161 subjects aged 18–69 from a questionnaire survey of the older Finnish Twin Cohort. Left-handedness was found to be more common in twins (8.1%) and triplets (7.1%) than in singletons (5.8%), whereas ambidextrousness was more common in triplets (6.4%) than in twins (3.4%) and singletons (3.5%). As in many other studies, males were more likely to be left-handed. Ambidextrous subjects were more likely to become right-handed writers even if not forced to use their right hand. We fit maximum likelihood models to our twin data to estimate the contribution of additive genetic, common environment and unique environmental effects to hand preference. Results, depending on the model, indicate that unique environmental effects account for most observed variance in handedness, both in childhood (92–100%) and adulthood (74–86%). When forced right-handedness was taken into account, estimates of familial effects increased. Concordance for left-handedness in twins is rare, and accordingly, very large samples are needed to detect the familial effects. Our results show that forced-handedness can have an effect on estimates of genetic effects.
ISSN:0028-3932
1873-3514
DOI:10.1016/j.neuropsychologia.2009.01.007