Fig. 1.

Causal links between PT, PE, and 2D:4D. As described by Zheng and Cohn (1), receptors for androgen and estrogen are present on digits 2 and 4 of the mouse but are most plentiful on the fourth digit. Chondrocyte proliferation is stimulated by PT but arrested by PE. Compared with females, males have higher levels of PT relative to PE and longer fourth digits relative to second digits. Thus, the sex difference in 2D:4D is dependent on prenatal changes in the fourth digit caused by sex-dependent differences in the PT-to-PE ratio. Examples of male and female human hands are shown for comparison.