The digital ratio is the ratio of the lengths of the different fingers on the hand generally measured from the midpoint of the bottom of the crease (where the finger meets the hand) to the tip of the finger. It has been suggested by some scientists that the two-digit ratio, in particular the 2nd (index finger) and 4th (ring finger), is different in men and women because of sex hormones.
Specifically, the assumption with 2D: 4D ratio is that the ring finger in men is longer than the index finger, while in women, these fingers are the same length or the index finger is longer than the ring finger. The ratio is believed to be due to differences in sex hormones, androgens, and estrogens, particularly during prenatal development. However, not all researchers agree with this theory .
The ratios between the lengths of the second and fourth finger, known as the 2D: 4D ratio, are different in men and women, which is often explained by the levels of androgens and estrogens. However, an alternative theory states that men have larger body parts , including the fingers, which affects the 2D: 4D ratio.
A research team that included academics from the University of HSE refuted this hypothesis by collecting data on finger lengths from 7,500 people. The results of the study were published in Scientific Reports .
To test this hypothesis, the researchers collected data on finger length and 2D: 4D ratio from more than 7,500 people, including representatives of the three major ethnicities, different ages, and nationalities; They then compared 2D: 4D ratios and finger lengths in these cohorts .
The lack of correlation between the total length of the fingers and the 2D: 4D ratio does not confirm the alternative explanation for the ratio differences in men and women based on the allometry hypothesis. Sex and sex hormone levels are likely to directly affect the 2D: 4D ratio. As Marina Butovskaya , Senior Researcher at the HSE International Center for Anthropology explains:
The 2D: 4D ratio is a sexually dimorphic characteristic, while its degree of sex and total differences varies from population to population. These variations can be explained by both genetic factors and specific environmental factors, such as nutrition and stress levels. The 2D: 4D ratio cannot be considered a universal masculinization marker, but it makes sense to use it among other indicators to assess the risks of estrogen abundance in embryos and the possible consequences for human health.