Digit Ratio & Behavior

Published January 29, 2013 by Tony

Evolution of human hands
Fingers & Personality

Show me your hand and I’ll tell you who you are!

The study on the hands never ceases to surprise us, after palmistry, foretelling the future through the study of the palm, others but more serious studies reveal our personality through the length of the fingers.

The digit ratio is the ratio of the lengths of different fingers (or digits).
Hand with index finger being shorter than the ring finger, resulting in the small ratio between  2D/4D, points to a high exposure to testosterone in the uterus.
The 2D:4D digit ratio is sexually dimorphic: while the second finger is typically shorter in both females and males, the difference between the lengths of the two digits is greater in males than females.
A number of studies have shown a correlation between the 2D:4D digit ratio and various physical and behavioral traits. There is some evidence that 2D:4D ratio may also be indicative for human development and growth. Hormones testosterone and estrogen exposure reflects in fetal life. Some authors suggest that digit ratio correlates with health, behavior, and even sexuality in later life. Below is a non-exhaustive list of some traits that have been either demonstrated or suggested to correlate with either high or low digit ratio.

•    Lowered sperm counts and high digit ratio
•    Increase risk for heart disease in males and high digit ratio
•    Risk of obesity and metabolic syndrome in males and high digit ratio
•    Reduced risk for prostate cancer and high digit ratio
•    Reduced birth size in males and high digit ratio
•    Increased risk for depression in males and high digit ratio
•     Reduced risk of alcohol dependency and high digit ratio
•    Increased Anxiety in males and high digit ratio
•    Reduced performance in sports and high digit ratio
•    Assertiveness in females and low digit ratio
•    Aggression in males and low digit ratio
•    Personality traits correlated with low or high digit ratio
•    Higher exam scores among male students and high digit ratio
•    Musical ability in males and low digit ratio

Paraphilic (or extreme fetish) sexual interest in males and high digit ratio.
• Bem female sex role score in women and high digit ratio; “feminine” erotic sex role preference in gay men and low digit ratio. [Finger-length patterns vary with gender, sexual orientation and birth order. Among heterosexuals, the mean 2D:4D ratio is larger in women than in men, especially on the right hand. The right-hand 2D:4D ratio of homosexual women is more masculine (that is, smaller) than that of heterosexual women. Men with more than one older brother are more likely to be homosexual and have a significantly more masculine right-hand 2D:4D ratio than men without older brothers.]

•    A smaller ratio between the second and fourth fingers is linked to a longer stretched penis size, (as reported by researchers in the Asian Journal of Andrology). [In this study, researchers at Gachon University Gil Hospital in South Korea recruited 144 volunteers 20 years of age and older who were going to undergo urological surgery. While the men were under anaesthesia, the researchers measured their finger lengths and both their flaccid and stretched penis lengths. Since shorter members stretch more than longer ones, the stretched measurement —used by the researchers— is more telling about the size of an erect penis, giving back that stretched penis length is statistically correlated to the size of the penis when fully erect. The average flaccid penis length, the researchers found, was 3.0 inches (7.7 centimetres), with a range of 1.6 to 4.7 in. (4 to 12 cm). Stretched lengths ranged from nearly 3.0 to 6.7 in. (7.5 to 17 cm), with an average of 4.6 in. (11.7 cm).The average ratio between the two fingers was 0.97, with a range of 0.88 to 1.12, making the differences hard to make out with the unaided eye. But the lower the digit ratio, the study found, the longer the penis was likely to be.]

It has been suggested by some scientists that the ratio of two digits in particular, the 2nd (index finger) and 4th (ring finger), is affected by exposure to androgens e.g. testosterone while in the uterus and that this 2D:4D ratio can be considered a crude measure for prenatal androgen exposure, with lower 2D:4D ratios pointing to higher androgen exposure. Studies in mice indicate that prenatal androgen acts primarily by promoting growth of the fourth finger.

Peter L. Hurd is an academic specialising in biology and his research primarily focuses on the study of the evolution of aggressive behavior, including investigation of aggression, communication and other behavior. He conducted a study on digit ratios suggesting a positive correlation in males between aggressive tendency and the ratio of the lengths of the ring finger to his index finger. Many studies on both human, and non-human, animals suggest that inter-individual variation in adult aggressiveness is largely organised by prenatal exposure to androgens. Men who have the ring finger longer than the index are more aggressive and quarrelsome.
Hurd demonstrated that men with more feminine typical-digit ratios showed lower aggressive tendency than males with more masculine-typical digit ratios. Hurd demonstrated that men with more feminine typical-digit ratios showed lower aggressive tendency than males with more masculine-typical digit ratios

Another study says that fighting may have shaped the evolution of the human hand, according to a new study by a US team. The University of Utah researchers used instruments to measure the forces and acceleration when martial artists hit a punch bag. They found that the structure of the fist provides support that increases the ability of the knuckles to transmit “punching” force.  David Carrier from the University of Utah, USA, suggests that the human hand may have also evolved its distinctive proportions for a less enlightened reason: for use as a weapon. According to Carrier and colleague Michael Morgan, modern chimpanzees have long palms and fingers with a short thumb, while the human palm and fingers are much shorter and the thumb longer and stronger. Carrier explains that this squat arrangement allows us to clench our hand into a fist when we fold the thumb across the fingertips; however, chimp fingers form an open doughnut shape when curled.

One comment on “Digit Ratio & Behavior

Pingback: 2015027. ¿Y si la endometriosis fuese el extremo opuesto del autismo? | Blog de Pere Losantos

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