The Ratio Between Index and Ring Finger

The ratio between index and ring finger is believed to be linked to exposure to the male hormone testosterone in the womb. On average, men tend to have longer ring fingers and women longer index fingers. The higher the testosterone, the greater the length of the ring finger and the more "masculine" the resulting child – whether male or female.

Why Men's Ring Fingers Are Longer Than Their Index Fingers: Male-Female Ring Finger Proportions Tied to Sex Hormones in Embryo

ScienceDaily (Sep. 6, 2011) — 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.

The finding could help medical professionals understand the origin of behavior and disease, which may be useful for customizing treatments or assessing risks in context with specific medical conditions.

Writing in the Proceedings of the National Academy of Sciences, developmental biologists 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 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.

It has long been suspected that the digit ratio is influenced by sex hormones, but until now direct experimental evidence was lacking.

"The discovery that growth of the developing digits is controlled directly by androgen and estrogen receptor activity confirms that finger proportions are a lifelong signature of our early hormonal milieu," Cohn said. "In addition to understanding the basis of one of the more bizarre differences between the sexes, it's exciting to think that our fingers can tell us something about the signals that we were exposed to during a short period of our time in the womb. There is growing evidence that a number of adult diseases have fetal origins. With the new data, we've shown that that the digit ratio reflects one's prenatal androgen and estrogen activity, and that could have some explanatory power."

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.

Since Roman times, people have associated the hand's fourth digit with the wearing of rings. In many cultures, a proportionally longer ring finger in men has been taken as a sign of fertility.
"I've been struggling to understand this trait since 1998," said John T. Manning, Ph.D., a professor at Swansea University in the United Kingdom, who was not involved in the current research. "When I read this study, I thought, thank goodness, we've attracted the attention of a developmental biologist with all the sophisticated techniques of molecular genetics and biology."

In dozens of papers and two books, including the seminal "Digit Ratio" in 2002, Manning has studied the meaning of the relative lengths of second and fourth digits in humans, known to scientists as the 2D:4D ratio.

"When Zheng and Cohn blocked testosterone receptors, they got a female digit ratio," Manning said. "When they added testosterone they got super male ratios, and when they added estrogen, super female ratios. And they've provided us with a list of 19 genes that are sensitive to prenatal testosterone and prenatal estrogen.

"I find this completely convincing and very useful," Manning said. "We can now be more focused in our examination of the links between digit ratio and sex-dependent behaviors, diseases of the immune system, cardiovascular disorders and a number of cancers."

Cohn, whose uses the tools of genetics, genomics and molecular biology to study limb development, said his lab began studying the digit ratios after Zheng became determined to find an explanation.
"He suggested that the 2D:4D ratio would be an interesting question, and I have to admit to being skeptical," Cohn said. "When he came back with the initial results, I was blown away. We looked at each others hands, then got busy planning the next experiment."

Finger Length Predicts Mental Toughness in Sport

ScienceDaily (Dec. 3, 2010) — Mental toughness and an aptitude for sport may be biologically determined.

This is one of the findings of an ongoing research project involving post-doctoral and doctoral research by Dr Jim Golby and Jennifer Meggs from Teesside University who will present their work on November 10 at the Division of Sport and Exercise Psychology's Annual Conference being held at the Holiday Inn London -- Camden Lock.

Previous research has shown that the 2D:4D ratio (index finger/ring finger) has the potential to explain sporting success. An index finger that is much shorter than the ring finger is caused by exposure to testosterone in the womb. This research investigated the relationship between 2D:4D and mental toughness, optimism, aggression and performance.

Sixty-seven participants had their fingers measured and completed personality and aggression questionnaires.

The results showed that participants with 2D:4D ratio were more likely to demonstrate mental toughness and have higher levels of sporting achievements.

Dr Golby explained: "It appears that high prenatal levels of testosterone may result in increased mental toughness, optimism and hence aptitude towards sport. This provides tentative support for the conclusion that mental toughness may be partially biologically predetermined."

Osteoarthritis Risk Linked To Finger Length Ratio

..............Professor Michael Doherty, lead researcher, said: “The 2D:4D length ratio appears to be a new risk factor for the development of OA. Specifically, women with the 'male' pattern of 2D:4D length ratio — that is, ring finger relatively longer than the index finger — are more likely to develop knee OA.”

As the first study to examine the relationship between 2D:4D length ratio and OA, it also raises questions.

Finger Length Points to Prostate Cancer Risk

The study led by The University of Warwick and The Institute of Cancer Research (ICR) found men whose index finger is longer than their ring finger were one third less likely to develop the disease than men with the opposite finger length pattern.

"Our results show that relative finger length could be used as a simple test for prostate cancer risk, particularly in men aged under 60," says joint senior author Professor Ros Eeles from the ICR and The Royal Marsden NHS Foundation Trust. "This exciting finding means that finger pattern could potentially be used to select at-risk men for ongoing screening, perhaps in combination with other factors such as family history or genetic testing.".......................

Don