Is 2d:4d a stable trait during child development?

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The second digit to fourth digit (2d:4d) ratio is a sexually dimorphic trait in humans that has been widely used to study male/female differences in other behavioral and morphological characteristics. 2d:4d is posited as a reliable indicator of prenatal androgen levels. We test this assumption by analyzing repeated digit measures collected over a 20-year period, including comparisons among maternally related siblings. Results indicate that 2d:4d increases with age for both males and females, suggesting that postnatal effects may influence dynamic changes in 2d:4d. Males with older brothers had higher 2d:4d while females with older brothers had lower 2d:4d. There was no effect of older sisters. The key hypothesis that 2d:4d is a stable trait fixed in utero is not supported.