Have you ever wondered what the lengths of your fingers could reveal about your character and personality traits? The digit index ratio, or 2D:4D ratio, might hold the fascinating key.
What is my digit ratio?
What is Digit Ratio?
The digit index ratio, or 2D:4D ratio, measures the length of a person’s index finger (2D) divided by their ring finger (4D). Influenced by prenatal androgen exposure, this ratio varies among individuals. It has been linked to various aspects of human biology and behavior, including personality traits, sexual orientation, and disease susceptibility [1].
Digit Ratio Formula
Here is the formula to calculate the digit ratio:
DR = 2D/4D
Where;
- DR: Digit Ratio
- 2D: Length of Index finger
- 4D: Length of Ring finger
Note:
A lower ratio indicates a longer ring finger compared to the index finger, while a higher ratio suggests a longer index finger relative to the ring finger.
Generally, the index finger (2D) is shorter in both males and females, with males typically showing a greater difference in length between the two digits than females.
How to Measure Your Finger Length?
Straighten your fingers and look at your palm. Focus on your index (second finger) and ring (fourth finger). Find the creases where these fingers meet your palm. Choose a point in the middle of each crease and mark it with a pen, if needed. Measure from this mark to the tip of each finger using a caliper, ruler, or tape measure with much accuracy.[2]
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Interpreting the Digit Ratio
The fascinating discovery is this: the ratio of your index to ring can indicate how much testosterone you were exposed to before birth (i.e. prenatal androgens), particularly during weeks 12-16 of gestation.
Analysis of amniocentesis samples has shown that the digit ratio is negatively correlated to prenatal testosterone, but positively to estrogen exposure. Put simply, our level of testosterone exposure, reflected in our digit ratio, correlates with the extent to which our brain and cognition exhibit masculine or feminine traits.[3]
Normal 2D:4D ratios are reported to be approximately 0.947 ± 0.029 for males and 0.965 ± 0.026 for females.
Masculine Ratio (Low Digit Ratio)
The lower the ratio, the higher the masculine traits (i.e. <0.94 in males and <0.97 in females).
- More perceived dominance and masculinity in a man’s face (e.g., broader face)
- Assertiveness in females and aggression in males
- Higher tendency toward non-monogamy
- Low levels of agreeableness
- High levels of emotional stability
- Low levels of verbal intelligence
- High levels of numerical intelligence
- Greater likelihood of left-handedness
- Enhanced numeracy skills compared to literacy in children
- Increased rates of ADHD and autistic traits
- Lower performance in empathic accuracy
- Elevated rates of alcohol dependence in men
Feminine Ratio (High Digit Ratio)
The higher the ratio, the higher the feminine traits (i.e. >0.94 in males and >0.97 in females).
- Decreased performance in sports
- Lowered sperm counts
- Increased risk for heart disease, obesity and metabolic syndrome
- Stronger tendency toward monogamy
- High levels of agreeableness
- Low levels of emotional stability
- High levels of verbal intelligence
- Low levels of numerical intelligence
- Greater levels of Big Five Openness, along with paranormal and superstitious beliefs
- Improved literacy skills compared to numeracy in children
- Increased likelihood of anxiety and depression in males
- Enhanced verbal fluency in both sexes and better visual recall in females
- Lower risk of developing alcohol dependency
Digit Ratio and Personality Traits
Enthusiasts of personality theories like Myers-Briggs may find it intriguing that your digit ratio aligns with your preference for Thinking (T) or Feeling (F).
Studies on congenital adrenal hyperplasia (CAH) show that children with CAH have lower, more “masculinized” 2D:4D ratios.[4] A meta-analysis found that lower 2D:4D ratios are linked to higher performance among elite athletes.
While a lower 2D:4D ratio, indicating higher prenatal testosterone may enhance performance under challenging conditions, it does not directly result in better physical performance or more goal-oriented behavior.[5] However, there is evidence that suggests a link between lower 2D:4D ratios and higher Dark Triad traits (i.e. Narcissism, Machiavellianism, Psychopathy).
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What Does a Lower Digit Ratio Indicate?
A lower Digit Ratio, i.e. less than 0.94 for males and less than 0.97 for females indicates more masculine characteristics.
What Does a Higher Digit Ratio Indicate?
A higher Digit Ratio, i.e. greater than 0.94 for males and greater than 0.97 for females indicates more feminine characteristics.
Can Digit Ratio Predict Disease Susceptibility?
Yes, certain studies show that the disease susceptibility correlates with the Digit Ratio.
For example, Hashimoto thyroiditis and Graves’ disease are autoimmune thyroid diseases that occur much more frequently in women than in men. Digit ratio (2D:4D) is thought to be a positive correlate of prenatal estrogen suggesting higher autoimmune thyroid disease susceptibility towards a higher digit ratio.[6]
2D:4D ratios may offer insights into the development and treatment of sex steroid-related cancers. The study findings indicate that women with lung cancer tend to have lower 2D:4D ratios and among these women, older age at diagnosis correlates positively with 2D:4D ratios. In men with lung cancer, those diagnosed with small-cell lung cancer exhibit lower 2D:4D ratios.[7]
Coronary heart disease (CHD) is more common in men and sexual hormones seem to play an important role in the development and protection against it. High androgen levels have been demonstrated to be linked with an increased risk for CHD.[8]
Is the Digit Ratio the Same for Both Hands?
The digit ratio between the hands can vary slightly based on factors such as race, gender, and age. However, it is generally relatively consistent between the left and right hands.
Wrapping It Up
The 2D:4D Ratio is a simpler, yet excessively studied ratio that shows multiple impacts on the physical, mental, and behavioral patterns of the individual. Sometimes as evidence suggests, the Digit Ratio may offer insights into the disease sensitivity of a particular individual.
The Digit Ratio may not vary in adults but the results can vary depending on the sex and age. The lower the ratio, the more masculine the traits are, which are very well observed in elite athletes.
References
- Swift-Gallant, A., Johnson, B. A., Di Rita, V., & Breedlove, S. M. (2020). Through a glass, darkly: Human digit ratios reflect prenatal androgens, imperfectly. Hormones and Behavior, 120, 104686. https://doi.org/10.1016/j.yhbeh.2020.104686
- Mayhew, T. M., Gillam, L., McDonald, R., & P. Ebling, F. J. (2007). Human 2D (index) and 4D (ring) digit lengths: Their variation and relationships during the menstrual cycle. Journal of Anatomy, 211(5), 630-638. https://doi.org/10.1111/j.1469-7580.2007.00801.x
- Bull, R., & Benson, P. J. (2006). Digit ratio (2D:4D) and the spatial representation of magnitude. Hormones and Behavior, 50(2), 194-199. https://doi.org/10.1016/j.yhbeh.2006.02.008
- Hönekopp, J., & Watson, S. (2010). Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand. American Journal of Human Biology, 22(5), 619-630. https://doi.org/10.1002/ajhb.21054
- Manning, J., Kilduff, L., Cook, C., Crewther, B., & Fink, B. (2014). Digit Ratio (2D:4D): A Biomarker for Prenatal Sex Steroids and Adult Sex Steroids in Challenge Situations. Frontiers in Endocrinology, 5, 75257. https://doi.org/10.3389/fendo.2014.00009
- Święchowicz, B., Kasielska-Trojan, A., Manning, J. T., & Antoszewski, B. (2022). Can Digit Ratio (2D:4D) Be Indicative of Predispositions to Autoimmune Thyroid Diseases in Women – Hashimoto Thyroiditis and Graves’ Disease? Frontiers in Endocrinology, 13. https://doi.org/10.3389/fendo.2022.914471
- Manning, J. T., Antczak, A., Dutkowska, A., Kuczyński, W., Sitek, A., & Antoszewski, B. (2020). Digit ratio (2D:4D) in women and men with lung cancer. Scientific Reports, 10(1), 1-8. https://doi.org/10.1038/s41598-020-68239-0
- McIntyre MH. The use of digit ratios as markers for perinatal androgen action. Reprod Biol Endocrinol. 2006 Feb 26;4:10. https://doi.org/10.1186/1477-7827-4-10