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The second to fourth digit ratio and asymmetry
John T Manning1, Bernhard Fink, Nick Neave
1Department of Psychology, University of Central Lancashire, Preston, UK.
Annals of Human Biology
|October 25, 2006
Summary
Both low and high second to fourth digit ratios (2D:4D), indicating different prenatal hormone levels, are linked to increased physical asymmetry, especially in finger development.
Area of Science:
- Developmental Biology
- Human Anatomy
- Endocrinology
Background:
- Deviations from bilateral symmetry are often linked to developmental environmental factors.
- Sex steroids, like testosterone and estrogen, are potential causes of developmental perturbations.
Purpose of the Study:
- To investigate the association between the second to fourth digit ratio (2D:4D) and physical asymmetry.
- 2D:4D is considered a marker for prenatal testosterone (negatively) and estrogen (positively).
Main Methods:
- Measured 11 physical traits, including finger lengths, in English children (n=680, ages 2-18).
- Assessed second to fifth finger lengths in Austrian/English undergraduates (n=120, ages 17-30) and Polish adults (n=213, ages 26-90).
Main Results:
- Found significant U-shaped associations between 2D:4D and all 11 traits in English children.
- Strongest links were observed between 2D:4D and asymmetry of the second/fourth digits and second to fifth digits.
- Confirmed significant U-shaped relationships between 2D:4D and finger asymmetries in student and adult samples.
Conclusions:
- Both low 2D:4D (high prenatal testosterone) and high 2D:4D (high prenatal estrogen) correlate with increased asymmetry.
- This relationship is particularly pronounced for finger asymmetry.
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