Martin Cohn, Ph.D., and Zhengui Zheng, Ph.D., of the Howard Hughes Medical Institute and the Department of Molecular Genetics and Microbiology at the University of Florida, recently discovered that the amount of testosterone and estrogen that an embryo receives in utero can have an effect on the size of ring and index fingers, thus giving a genetic explanation to many of the 2D:4D ratio findings. In this study, published in this week's edition of Proceedings of the National Academy of Sciences of the United States of America (PNAS), they used pregnant mice, which have similar digit ratios as humans, and increased the estrogen and testosterone levels during a certain part of the pregnancy. The males that received more estrogen had not only a longer index finger, but also a more feminine appearance.
These findings not only offer an explanation for why females generally have longer index and males longer ring fingers, but also for a wide range of studies that have linked the 2D:4D ratio to things such as prostate cancer, ADHD, aggression, personality, sensory perception, sexual orientation and much more.
When asked about the study, Dr. Cohn mentions that he was skeptical at first but "blown away" by the initial results and admits to first taking a closer look at his own hands and at the hands of his fellow researcher.
For more information on many of the findings related to the 2D:4D ratio, take a look at: http://en.wikipedia.org/wiki/Digit_ratio
.... and have fun comparing your index to your ring finger and to those of others around you!