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Digit Ratio: A Pointer to Fertility, Behavior, and Health (A volume in the Rutgers Series in Human Evolution, edited by Robert Trivers.) Paperback – February 1, 2002


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Product Details

  • Paperback: 192 pages
  • Publisher: Rutgers University Press; First Edition edition (February 1, 2002)
  • Language: English
  • ISBN-10: 081353030X
  • ISBN-13: 978-0813530307
  • Product Dimensions: 9.4 x 6.1 x 0.5 inches
  • Shipping Weight: 11.2 ounces (View shipping rates and policies)
  • Average Customer Review: 3.0 out of 5 stars  See all reviews (2 customer reviews)
  • Amazon Best Sellers Rank: #2,054,339 in Books (See Top 100 in Books)

Editorial Reviews

From the Back Cover

Could the length of your fingers indicate 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 hormone- 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 (2D) and ring (4D) 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 traits ranging from sperm counts, family size, musical genius, and sporting prowess, to autism, depression, homosexuality, heart attacks, and breast cancer, traits that are all linked with early exposure to sex hormones.

About the Author

John T. Manning is a senior lecturer in biological sciences at the University of Liverpool, U.K., and a founding member of the Rutgers University Jamaican Fluctuating Asymmetry Project.

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Most Helpful Customer Reviews

18 of 18 people found the following review helpful By ChefBum on July 26, 2005
Format: Paperback Verified Purchase
This book by John T. Manning, who is apparently the leading authority on digit ratio and its biological/hormonal causes.

To summarize: this book posits and goes about proving how prenatal testosterone levels affect the masculinazation of the fetus, resulting in a low 2d:4d digit ratio. This ratio is the ratio of finger length of the index finger vis-a-vis the ring finger on the same hand. Masculine ratios are under 1.0, meaning that the index finger is shorter than the ring finger. Feminine ratios are generally 1:1 or the index finger is slightly longer than the ring finger. Manning also goes on to determine how this ratio may be an indicator of adult masculine traits, such as athletic ability, musical ability, and physical aggressiveness and assertiveness.

What this book does right:

1. It's more of a textbook than casual reading. It presents copious data and is immaculately presented and organized in easy to read fashion. It is easy to refer back to over and over again, as it should be with good reference material;

2. As such, this book will dispel any disbelief in what is considered a mildly controversial topic in mainstream news. People are still uncomfortable with the fact that something as obvious as the finger length on their hands can tell a lot about them, even to total strangers;

3. Despite the copious anecdotal evidence and hard data, Manning does exercise due caution in jumping to conclusions about where this area of study may lead;

4. The prose is very succinct and to the point. Though only around 170 pages, it is packed with information;

This book only gets four stars because of some minor quibbles. First, it is not a book that will entertain the casual science reader.
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1 of 3 people found the following review helpful By Suzanne on January 5, 2009
Format: Paperback
Bottom line: a must-read for people interested in the biological origins of homosexuality.

Many deep secrets are right at our fingertips! Literally! But get ready to wade through plenty of dry prose and lots of graphs to find out.

This book explains what scientists have learned about neurobiology and genetics from studying finger lengths. You can participate in this ongoing research on the web at the BBC. Preliminary results are in from controlled studies, and they give the clearest picture so far of the origins of homosexuality in men, which appears to correlate with the fetus and the fetal brain being marinated in high concentrations of testosterone at a very specific point in early pregnancy--a point that also determines the ratio of your index finger to your middle finger on your dominant hand. The author can only speculate why the mother's body reacts to the viable embryo with this particular hormonal response, and it is noted (as has been noted elsewhere in popular science) that first-born sons are less likely to be gay than subsequent male offspring of the same mother. More data is required to correlate digit ratio with female homosexuality, and the book goes into several other useful applications of the findings for medical diagnostics.
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