Finger ridge-counts correlate with the second to fourth digit ratio [pre-print]

Objectives. This study examined the relationship of finger ridge-counts to second to fourth digit ratio, which has not yet been definitively demonstrated. The related question of sex dimorphism in finger ridge-counts was further elucidated.

Methods. A sample of Germans, including 1,134 males and 1,031 females, was examined for sex dimorphism in the finger ridge-counts. Second and fourth digit lengths were measured in a sub-sample of 80 males and 86 females to compute second to fourth digit ratio. Principal component scores were obtained to investigate sex dimorphism and the correlation between ridge-counts and digit ratio. Regression and analysis of covariance were used to investigate relationships.

Results. Males generally have higher ridge-counts than females. Subtle dimorphic features emerged from the principal components, like a contrast between digits 2 and 4, suggesting a ratio analogous to the digit ratio. The most dimorphic feature was digit 1 asymmetry, males exhibiting a stronger right bias than females. Digit ratio was significantly related to four principal components, expressing various contrasts among digits. Other relationships involved contrast between digits 3 and 5 and asymmetry on digits 1 and 2.

Conclusions. This paper provides definitive evidence that finger ridge-counts correlate with second to fourth digit ratio. The most important finding was associations of ridge-counts with digit ratio did not involve commonly used summary counts over all digits. Rather, associations acted more locally, in ways paralleling the digit ratio, in others reflecting asymmetry. The results strongly support the idea that sex hormones affect finger ridge-counts.

This is a pre-print/pre-peer reviewed version of the following article:

Jantz, R. L. (2021). Finger ridge-counts correlate with the second to fourth digit ratio (2d:4d). American Journal of Human Biology, e23625. https://doi.org/10.1002/ ajhb.23625

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The post-print/accepted version of the article is also available in TRACE: https://trace.tennessee.edu/utk_anthpubs/8/