Here is some new info:
http://news.ufl.edu/2011/09/06/male-female-ring-finger/Male-female ring finger proportions tied to sex hormones in embryo; may offer health insights
Filed under Gender, Health, Research on Tuesday, September 6, 2011. GAINESVILLE, Fla. — Biologists at the University of Florida have found a reason why men's ring fingers are generally longer than their index fingers — and why the reverse usually holds true for women.
Writing this week in the Proceedings of the National Academy of Sciences, developmental biologists Martin Cohn and Zhengui Zheng of the Howard Hughes Medical Institute and the department of molecular genetics and microbiology at the UF College of Medicine, show that male and female digit proportions are determined by the balance of sex hormones during early embryonic development. Differences in how these hormones activate receptors in males and females affect the growth of specific digits.
The discovery provides a genetic explanation for a raft of studies that link finger proportions with traits ranging from sperm counts, aggression, musical ability, sexual orientation and sports prowess, to health problems such as autism, depression, heart attack and breast cancer.
Cohn and Zheng, also members of the UF Genetics Institute, found that the developing digits of male and female mouse embryos are packed with receptors for sex hormones. By following the prenatal development of the limb buds of mice, which have a digit length ratio similar to humans, the scientists controlled the gene signaling effects of androgen — also known as testosterone — and estrogen.
Essentially, more androgen equated to a proportionally longer fourth digit. More estrogen resulted in a feminized appearance. The study uncovered how these hormonal signals govern the rate at which skeletal precursor cells divide, and showed that different finger bones have different levels of sensitivity to androgen and estrogen.
