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Updated: Jan 13, 2026
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Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila
Published on: October 1, 2011
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The First Allometric Analysis in Newborns Rejects the Allometry Hypothesis for 2D:4D: Strong Developmental Evidence
Barış Özener1, Berna Ertuğrul1, Görel Aksoy1
1Department of Anthropology, Istanbul University, Istanbul, Turkiye.
Summary
Male newborns show a lower second-to-fourth digit length ratio (2D:4D) than females, indicating prenatal hormonal influences. This sex difference in 2D:4D is independent of overall digit size, supporting hormonal programming over growth interactions.
Area of Science:
- Developmental Biology
- Human Anatomy
- Endocrinology
Background:
- The second-to-fourth digit length ratio (2D:4D) is a proposed marker for prenatal androgen exposure.
- Investigating this ratio in newborns can elucidate early developmental influences.
Purpose of the Study:
- To assess sexual dimorphism in the 2D:4D ratio among Turkish newborns.
- To determine if allometric interactions influence 2D:4D sexual dimorphism in neonates.
Main Methods:
- Digit lengths (2D and 4D) were precisely measured for both hands in 225 Turkish newborns.
- Statistical analyses including ANOVA and ANCOVA were employed, with 4D length as a covariate.
Main Results:
- Male newborns exhibited significantly lower 2D:4D ratios compared to females.
- This sexual dimorphism persisted even after controlling for the fourth digit (4D) length.
- The second digit (2D) length itself showed significant sex differences when 4D length was controlled.
Conclusions:
- Evidence of 2D:4D sexual dimorphism in Turkish neonates was found.
- The findings suggest that 2D:4D dimorphism is primarily driven by prenatal hormonal programming, not postnatal allometric growth.
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