Look at the difference in length between your index (pointer) finger and your ring finger. That difference is called the digit ratio. It's calculated by dividing your index finger length by your ring finger length. AncestryDNA® can tell you if your DNA suggests your index finger may be longer than your ring finger - or vice versa.
Index to Ring Finger Ratio
Most often the index finger is shorter than the ring finger in both males* and females*. But if you look across a population, you'll see variation. Some people have longer ring fingers while others do not. Why is that?
Some of the variation in ratios is due to genetics. So a significantly longer ring finger for instance could be partly due to the DNA you get from your parents.
But your digit ratio is also related to how much of the male sex hormone testosterone you were exposed to in the womb. Greater testosterone exposure experienced by male fetuses means males tend to have smaller digit ratios.
Genetics of Your Digit Ratio
SMOC1 gene on chromosome 14 and the LIN28B gene on chromosome.
Both the SMOC1 gene and the LIN28B gene are involved in early limb development, and DNA differences in these genes may help determine your digit ratio.
Now how does genetics relate to other factors that impact digit ratios like sex hormone levels? Scientists are still trying to determine whether it's the genes that are controlled by sex hormone levels or the other way around.
What Science Says About Your Digit Ratio
Is there a connection between how long your ring finger and index finger are and other factors - like how good you are at sports? Or how good your sense of direction is?
Though not without controversy, the volume of studies looking for connections between your digit ratio and other characteristics and conditions has accelerated in recent years.
And in some of these studies, the digit ratio has been shown to have a correlation with a wide range of conditions and traits including obesity, attention deficit disorder, autism, prostate cancer, visuo-spatial ability (sense of direction), athletic performance, and more.
Interesting Facts About Your Digit Ratio
If you're a twin, there's another twist to how much longer (or shorter) your ring finger is compared to your index finger: the gender of your twin. Females with male twins will have a longer ring finger than they might have had otherwise, thanks to the male twin's testosterone they were exposed to in the womb.
And the digit ratio you have today is probably the same one you were born with. This is because as you develop into adulthood, your limbs tend to grow by the same proportions. So even though both your index finger and ring finger got longer, they both got longer by about the same amount.
*Assigned sex at birth
Collaer ML, Reimers S, Manning JT. Visuospatial performance on an internet line judgment task and potential hormonal markers: sex, sexual orientation, and 2D:4D. Arch Sex Behav. 2007;36(2):177-192. doi:10.1007/s10508-006-9152-1.
Hines M, Constantinescu M, Spencer D. Early androgen exposure and human gender development. Biology of Sex Differences. 2015;6(1). doi:10.1186/s13293-015-0022-1.
Jeevanandam S. 2D:4D Ratio and its implications in medicine. Journal of Clinical and Diagnostic Research. 2016. doi:10.7860/jcdr/2016/21952.9000.
Lawrance-Owen AJ, Bargary G, Bosten JM, Goodbourn PT, Hogg RE, Mollon JD. Genetic association suggests that SMOC1 mediates between prenatal sex hormones and digit ratio. Human Genetics. 2012;132(4):415â€“421. doi:10.1007/s00439-012-1259-y.
Medland SE, Zayats T, Glaser B, et al. A variant in LIN28B is associated with 2D:4D finger-length ratio, a putative retrospective biomarker of prenatal testosterone exposure. The American Journal of Human Genetics. 2010;86(4):519â€“525. doi:10.1016/j.ajhg.2010.02.017.
The neuroscience of finger length and athletic prowess. Psychology Today. October 14, 2016. https://www.psychologytoday.com/us/blog/the-athletes-way/201610/the-neuroscience-finger-length-ratio-and-athletic-prowess
Weinberg SM, Parsons TE, Raffensperger ZD, Marazita ML. Prenatal sex hormones, digit ratio, and face shape in adult males. Orthod Craniofac Res. 2015;18(1):21-26. doi:10.1111/ocr.12055.
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