No abstract

The lengths of the index finger (2D) and ring finger (4D) are sexually dimorphic in humans, and men have a smaller 2D:4D ratio compared to women. Prenatal androgens appear to be important in the development of the 2D:4D sex difference, since it has been reported in children as young as 2 years old, and since humans exposed to supernormal prenatal androgen levels display a smaller 2D:4D ratio. We tested whether another mammalian species in which the process of peripheral sexual differentiation is androgen-dependent might also show a sex difference in digit ratios. The 2D:4D ratio of adult outbred mice was calculated for both the left and right rear paws. A sex difference was observed in the right rear paw: female mice had a larger 2D:4D ratio than did males. We also found this difference in prepubescent weanling mice. This sex difference is in the same direction as that observed in humans, and suggests that sexual dimorphism in digit length ratios is a feature common to many, if not all, mammals. The mouse may therefore be a useful animal model for studying the factors that influence finger length patterns, which have recently been correlated with several specific behaviors and disease predispositions in humans. Anat Key words: digit ratios; sex difference; mice; adult; weanling A nineteenth-century anthropological report (Ecker, 1875) noted that when asked whether the index or the ring finger was longer, people tended to look at their own hand, and the answer depended on the sex of the person. Men generally reported that the ring finger was longer, whereas women more often stated that the index finger was longer. For over 50 years there were conflicting reports about whether there is truly a sex difference in the pattern of finger lengths, until George (1930) standardized a method of measuring fingers, gathered a large sample of subjects, and showed that the sex difference was statistically significant. This sex difference has recently been reformulated as the ratio of the length of the index finger (2D) to the length of the ring finger (4D). This ratio is indeed sexually dimorphic in humans: men have a smaller 2D:4D ratio on average than do women. The sex difference in the 2D:4D ratio is evident, and stable, from 2 years of age though adulthood (Manning et al., 1998).Since the 2D:4D ratio sex difference appears to be unaffected by changing sex hormone levels at puberty, and since most other mammalian sex differences are androgen-dependent (Breedlove et al., 1998), prenatal androgen levels may play a role in digit length development. Supporting this supposition is the finding that individuals with congenital adrenal hyperplasia (CAH) display masculinized finger length patterns (Brown et al., 2001). CAH is a disorder that causes the developing fetus to produce excessive adrenal androgens. Hormone levels are usually normalized at birth, so physical and behavioral differences between CAH and non-CAH individuals can primarily be attributed to the effects of supernormal prenatal androgens. This result further...

No abstract

The physiological and psychological effects of 2 human sex-steroid derived compounds, 4.16-androstadien-3-one (AND) and l,3,5(10),16-estratetraen-3-ol(EST) were measured in 24 subjects who participated in a within-subjects, double-blind experiment. A dissociation was evident in the physiological effects of AND, in that it increased physiological arousal in women but decreased it in men. EST did not significantly affect physiological arousal in women or men. Neither compound significantly affected mood. AND is an androgen derivative that is the most prevalent androstene in human male sweat, male axillary hair, and on the male axillary skin surface. The authors argue that AND's opposite effects on physiology in men and women further implicate this compound in chemical communication between humans.

There is indirect evidence that heightened exposure to early androgen may increase the probability that a girl will develop a homosexual orientation in adulthood. One such putative marker of early androgen exposure is the ratio of the length of the index finger (2D) to the ring finger (4D), which is smaller in male humans than in females, and is smaller in lesbians than in heterosexual women. Yet there is also evidence that women may have different sexual orientations at different times in their lives, which suggests that other influences on female sexual orientation, presumably social, are at work as well. We surveyed individuals from a gay pride street fair and found that lesbians who identified themselves as "butch" had a significantly smaller 2D:4D than did those who identified themselves as "femme." We conclude that increased early androgen exposure plays a role in only some cases of female homosexuality, and that the sexual orientation of "femme" lesbians is unlikely to have been influenced by early androgens.