Digit length ratio (2D:4D) and variation in key life-history traits and fitness in contemporary Finnish women

The ratio of second-to-fourth digit length (2D:4D) has been suggested to reflect prenatal steroid levels, which likely bear important consequences for vertebrate adult-age physiology, behavior, and reproductive success. The evidence for 2D:4D being related to individual fitness comes largely from studies in humans. These studies have not, however, been conclusive as important confounding factors affecting completed family size (e.g., socioeconomic status) have not been accounted for and the vast majority of the participants examined have not yet ended their reproductive careers. In addition, the life-history traits generating such fitness differences have received less attention in the literature. We studied whether 2D:4D was associated with several life-history traits (probability of reproducing, adulthood height, ages at first and last reproduction, and interbirth intervals) and fitness (the number of offspring raised to adulthood) in postreproductive Finnish women, while controlling for education and spatio-temporal variation of traits. We found no association between 2D:4D and the life-history traits studied and fitness among these Finnish women. These results thus cast doubts to the claim that 2D:4D predicts female life histories and evolutionary fitness in humans. Copyright 2010, Oxford University Press.