No association between two candidate markers of prenatal sex hormones: Digit ratios (2D:4D and other) and finger‐ridge counts

The second‐to‐fourth digit ratio (2D:4D), putatively indexing prenatal androgen levels retrospectively, has become increasingly popular as an easily applied measure in research into the prenatal sex‐hormonal bases of behavior, health, and disease. However, its validity has not yet been conclusively demonstrated and in fact is currently debated, because validation tests of 2D:4D with other, prenatally established, presumed markers for prenatal sex‐hormone action have yielded mixed evidence or still are unavailable. Hence, the associations of 2D:4D with finger‐ridge counts, one such further under‐researched marker, were examined in this study. In a sample of 75 male and 75 female normal healthy adults, the six possible finger‐length ratios of the human hand (from 2D:3D to 4D:5D, including the classic 2D:4D ratio) were ascertained with two commonly used measurement methods (imaged‐based vs. fingers measured directly), along with two traditional dermatoglyphic traits (total and absolute finger‐ridge counts). Sex differences in finger‐length ratios (lower in men) generally were of moderate size (about .5 SD units), whereas those in finger‐ridge counts (higher in men) were small to negligible (about .2 SD units). Within‐sex analysis did not indicate theory compliant (i.e., negative) correlations between these two sets of traits that were consistent, noteworthy, or reliable. Finger‐length ratios and finger‐ridge counts are ontogenetically overlapping in their prenatal formation and anatomically adjacent. Hence, possible temporal and localized sex‐hormonal effects in prenatal life are unlikely to account for their nonassociation. The current findings cast some doubt on the validity of these retrospective pointers to prenatal androgen levels. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 53: 69–78, 2011.