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Digit ratio is everywhere. My friend recently sent me a copy of a paper he wrote on digit length and ALS, which has been accepted for publication in a scientific journal. After reading it, I stumbled upon Scicurious blog posting on digit length and sumo wrestlers. Seriously, is there anything not linked to digit ratio? There’s even a blog dedicated to digit ratio.

Digit ratio is determined by comparing the length of the 2nd (index) and 4th (ring) finger. This ratio is referred to as 2D:4D. A low 2D:4D ratio (longer 4th finger) is associated with higher testosterone exposure in the uterus and typically male. A higher 2D:4D ratio (shorter 4th finger) means a lower exposure to testosterone in the uterus and typically female.

First mentions of digit ratio are often given to Johan Alexander Ecker, a German anthropologist who published “Einige Bemerkungen über einen Schwankenden Charakter in den Hand des Menschen[Some remarks about a varying character in the hand of humans]” in 1875 in Archiv fur Anthropologie (Ecker founded the journal, which was the first German journal of anthropology).  And, to Frank Baker, professor of anatomy at University of Georgetown. Baker published the paper, “Anthropological notes on the human hand,” in 1888 in The American Anthropologist. Baker cites Ecker in his paper, which begins as musings on the odd uses of both attached and severed hands of the dead in world cultures. I think both men would be amazed and perhaps confounded at all the things 2D:4D is linked to today.

Over the past 5 years, I’ve been reading articles discussing 2D:4D or watching documentaries on the subject. Finger length has been tied to a host of physical and psychological traits. More for me than anything else, I needed to sort out and itemize the list

ADHD: A 2009 study in The Journal of Child Psychology and Psychiatry of 312 children (168 diagnosed with ADHD and 144 non-ADHD) found a link between low 2D:4D and ADHD symptoms. A 2010 study in Behavioral Neuroscience found a similar result with boys and finger length, but saw less evidence in girls.

Alcohol dependency:  Researchers reported in PlosOne a lower 2D:4D ratio as an indicator of alcohol dependency from a study comparing 131 alcohol dependent patients and 185 healthy participants.

ALS: A study in the Journal of Neurology, Neurosurgery and Psychiatry links a lower 2D:4D ratio to higher risk of sporadic ALS.

Athletic prowess: The British Journal of Sports Medicine published results of a study of 607 women, that found women with a low 2D:4D ratio exhibited marked increased athletic ability. Studies on men comparing athletic abilities and digit length are often narrowed down into specific sports, such as skiing, football, basketball, soccer and sumo wrestling!

Attractiveness: In April, researchers submitted a study to the Proceedings of the Royal Society B suggesting the 2D:4D ratio predicts facial attractiveness in men.  The more masculine (or lower 2D:4D ratio) the more attractive is the man’s face.

Autism: A 2001 paper in Developmental Medicine and Child Neurology suggested a low 2D:4D may be linked to autism as a result of high concentrations of prenatal testosterone.  The study further revealed that not only the children, but the siblings and parents also had lower 2D:4D ratios. Children with Asperger’s Syndrome, though having a lower 2D:4D ratio than population norms, did have a higher ratio than children with autism.

Congenital adrenal hyperplasia (CAH): Hormones and Behavior reported that  women with CAH were found to have a lower 2D:4D ratio compared to women without CAH. Males with CAH have a smaller digit ratio on the left hand than control males.

Depression: Dr. John Manning (author of “Digit ratio: a pointer to fertility, behavior, and health”) and his team at The University of Liverpool found a link between finger length and depression. A longer ring finer (4th finger) resulted in a higher chance of depression, but only in men and not in women.

Heart Disease: In 2005, researchers posited in the International Journal of Obesity that men with a low 2D:4D ratio were older when they had myocardial infarction (MI) compared with men who had a higher ratio and were younger at their first MI.

High-frequency financial traders:  Researchers in Proceedings of the National Academy of Sciences looked at the hands of a group of male traders who worked in high-frequency trading and found men with a lower 2D:4D had more long-term profitability and remained in the business longer.

Left-handedness: A 2008 study at University of Melbourne looked at 600 students and determined that a lower 2D:4D ratio was associated with left-handedness. As well, they reported longer finger lengths on the left hand of left-handed subjects and longer fingers on the right hand of right-handed subjects.

Penis length: A Korean study in the Asian Journal of Andrology linked a low 2D:4D ratio to penile length. Researchers looked at 144 men who were hospitalized for urology surgery and compared their digit ratio to the length of their penis. Examinations were carried out under anaesthesia so, no faking us out on this one.

Prostate cancer: A 2010 study in the British Journal of Cancer found a higher 2D:4D ratio marked a decreased risk of prostate cancer. However, a study this year in the same journal counters the 2010 findings with the conclusion that there is not a clear association between 2D:4D and prostate cancer risk.

Schizophrenia: According to a 2004 study in Progress in Neuro-Psychopharmacology and Biological Psychiatry, a higher 2D:4D was found in schizophrenic men and women.

Sexual Orientation: A 2000 study in Nature examined the link between digit ratio and homosexual women, who had a lower ratio than heterosexual women.  Studies on gay men and finger length are contradictory showing both high and low-level ratios in finger length. Women, however had more straight forward results, with lesbians being more likely to have a lower ratio than heterosexual women. In a 2002 study in Archives of Sexual Behavior, researcher Windy Brown, of UC Berkeley, noted that one could further break down the ratio and discovered women who define themselves as “butch” had a significantly smaller 2D:4D than women who defined themselves as “femme.”

So, got all that? If you have a low 2D:4D ratio, you are at increased odds of being male and having: ADHD, alcohol dependency, sporadic ALS, autism, CAH, prostate cancer, and depression. On the plus side, you are also at a lower risk for early heart disease and are probably handsome and athletic.

To measure your 2D:4D ratio, with your right hand flat measure the length of your 2nd and 4th fingers from the bottom crease where the finger meets the hand to the tip of the finger. Divide the length of the 2nd finger by the length of the 4th. A longer index finger (2nd) will give a ratio higher than 1. A longer ring finger (4th) will give a ratio lower than 1.

Got your results? Now see if you can predict your risk of disease, your level of intelligence and athleticism, the measure of your earning power and success at taking examines and whether or not you are a candidate for sumo wrestling and high-frequency trading. Frankly, I hope you get the ratio of 1 so everything in life will still be a surprise and you won’t have your fingers to blame!

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