Digit Ratio: A Pointer to Fertility, Behavior, and Health

Abstract

This new series presents innovative titles pertaining to human origins, evolution, and behavior from a multi-disciplinary perspective. Subject areas include but are not limited to biological and physical anthropology, prehistoric archaeology, evolutionary psychology, behavioral ecology, and evolutionary biology. The series volumes will be of interest primarily to students and scholars in these fields.Could the length of your fingers predict a predisposition to breast cancer? Or musical genius? Or homosexuality? In Digit Ratio, John T. Manning posits that relative lengths of the second and fourth digits in humans (2D:4D ratio) does provide such a window into fertility-and sex-related traits.It has been known for more than a century that men and women tend to differ in the relative lengths of their index and ring fingers, which upon casual observation seem fairly symmetrical. Men on average have fourth digits longer than their second digits, while women typically have the opposite. Digit ratios are unique in that they are fixed before birth, while other sexually dimorphic variables are fixed after puberty, and the same genes that control for finger length also control the development of the sex organs. The 2D:4D ratio is the only prenatal sexually dimorphic trait that measurably explains conditions linking testosterone, estrogen, and human development; the study of the ratio broadens our view of human ability, talent, behavior, disposition, health, and fertility. In this book, Manning presents evidence for how 2D:4D correlates with genetic traits ranging from sperm counts, the likelihood of having male versus female offspring, musical genius, and sporting prowess, to autism,depression, homosexuality, heart attacks, or breast cancer, traits that are all linked to sex hormones.