Over the past decade, the correlation of digit ratio with sexual behavior and other aspects of reproductive biology have been well documented and there is a growing list of traits with links to digit ratio, although the associations are less well established.
The key to this relationship may lie in the womb. In Ho Choi of Gacheon University Gil Hospital in Incheon explains:
"During the fetal period, high concentrations of testosterone lead to high testicular activity, resulting in a lower digit ratio. In the present study, patients with a lower digit ratio tended to have a longer stretched penile length."
Choi and colleagues compared the digit ratios of 144 Korean men aged 20 and older who were being treated for urological surgery. Researchers measured the index and ring fingers of each man's right hand and compared the ratio to the length of each man's fully stretched, flaccid penis (the latter data obtained under anesthesia).
In a journal commentary, Denise Brooks McQuade of Skidmore College, Saratoga Springs, N.Y., said the study results "provide convincing support for a relationship between digit ratio and penile length." She added that the findings might have real value for research into clinical conditions linked to developmental issues in men.
A non-erect penis usually measures between 8.5cm and 10.5cm (3-4 inches) from tip to base. The average size is about 9.5cm (3.75 inches). Many factors can cause a temporary shrinkage of two inches or more, for instance cold weather or going swimming can effect an accurate measurement.
It is a fact though that some men have big penises and some have smaller ones, just as some men have small feet and some have big feet, but the measurement is not an index of virility.
Most people think that a tall man will usually have a large penis, but this is not entirely true. The largest organ recorded was 14 cm (5.5 inches) in the flaccid state. It belonged to a slim man who was 5' 7" tall (170 cm). The smallest penis measured 6cm (2.25 inches). It belonged to a fairly heavily built man of 5' 11" (180cm).
Scientists from the United Kingdom also did research comparing finger size and the likelihood of patients getting cancer of the prostate.
They adopted a questionnaire format in order to secure over 1500 prostate cancer patients and over 3000 controls. Participants matched hand patterns with one of three drawings supplied by the researchers: index finger shorter than ring finger (low digit ratio); index finger equal to ring finger; or index finger longer than ring finger (high digit ratio). Participants with index finger longer than ring finger were significantly less likely to have prostate cancer and the authors concluded that high digit ratio may confer a protective effect against the disease.