Males and females generally have different finger proportions. In males, digit two, the index finger, is shorter than digit four, but in females digit two is the same length or longer than digit four. There has been much discussion in the media about how the ratio of a man’s index to fourth digit is indicative of masculine traits. The greater the ratio of fourth to second, the higher his libido, the greater his sperm count, his sporting prowess, etc.
Now, a study in mice, suggests that the growing limb buds respond to androgen and estrogen differentially. This controls the cell proliferation, leading to the opposite finger length ratio in males and females. The study shows that the ratio of second to fourth digit length is a lifelong indicator of pre-natal exposure and could be important for the identification of pre-natal endocrine disruption in mammals, perhaps caused by chemical pollution, and in tracing the fetal origins of adult disease.
- Developmental basis of sexually dimorphic digit ratios
Z. Zheng, M. J. Cohn,
Proc. Natl. Acad. Sci. 2011, 108, 16289-16294.