Original Research Article
Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand
Article first published online: 11 MAY 2010
Copyright © 2010 Wiley-Liss, Inc.
American Journal of Human Biology
Volume 22, Issue 5, pages 619–630, September/October 2010
How to Cite
Hönekopp, J. and Watson, S. (2010), Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand. Am. J. Hum. Biol., 22: 619–630. doi: 10.1002/ajhb.21054
- Issue published online: 19 AUG 2010
- Article first published online: 11 MAY 2010
- Manuscript Accepted: 27 FEB 2010
- Manuscript Revised: 22 FEB 2010
- Manuscript Received: 31 OCT 2009
Our aims are, first, to describe the sex difference in the length ratio of the second and fourth digits (2D:4D), which likely reflects prenatal testosterone levels in humans. Second, to infer the loss of reliability observed in 2D:4D based on self-measured finger lengths.
We used random-effects meta-analysis of 2D:4D based on expert-measured finger lengths (116 samples with 13,260 females and 11,789 males).
We find a moderate sex difference (with lower 2D:4D for males), which shows substantial heterogeneity (which is unrelated to age). The sex difference is moderated by the type of finger length measurement and by hand. Measurement involving the distortion of soft tissue leads to a significantly larger sex difference than finger length measurement avoiding this. The sex difference in 2D:4D is larger in the right hand than in the left. The reliability of self-measured 2D:4D in the BBC internet study, by far the largest study on 2D:4D, is estimated to be 46% of that of expert-measured 2D:4D.
Right-hand 2D:4D might be a better indicator of prenatal androgenisation than left-hand 2D:4D. The view that 2D:4D has allometric properties (Kratochvil L, Flegr J. 2009. Differences in 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line. Biol Lett 5:643–646.) is not supported. Bone lengths contribute to the sex difference in 2D:4D. In addition, there might be a sex difference in fingers' soft tissue, which should be investigated. Because of measurement unreliability, correlations between 2D:4D and variables of interest are about one-third smaller in the BBC internet study than in studies in which 2D:4D is based on expert-measured finger lengths. Am. J. Hum. Biol. 22:619–630, 2010. © 2010 Wiley-Liss, Inc.