Researchers say that the length of a man’s index finger compared to his ring finger on his right hand is an indicator of his testicle size.
And the study claims that the digit ratio could be used to predict testicle volumes of any male.
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The study was carried out by South Korean researchers from the Department of Urology at Gachon University Gil Hospital in Incheon and Seoul National University Hospital.
They found that adult males with a ring finger longer than their index finger on their right hand had larger testicles.
Conversely, men with a longer index finger compared to their ring finger have smaller testicles.
Prior to the study it had already been suggested that second to fourth digit ratio correlated with the male reproductive system.
This was based on the finding that Hox genes – which help lay out how a person’s body takes shape – control finger development and genital development during the embryonic stage.
Previous research has suggested that the size of a man’s testicle correlates with the volume of semen he produces.
In the study a total of 172 Korean men aged 20 to 69 years, already hospitalised for urological surgery, were enrolled.
First, the researchers measured the length of the second and fourth digits of each participant.
Then, separately and independently, an experienced urologist measured their testes size.
The results then showed that digit ratio was inversely proportionate to adult testicular volume – meaning that a longer ring finger correlated to larger testicles and vice versa.
In the study the researchers also found that age and height did not have much effect on testicular volume, while weight had a marginal correlation.