The 2nd:4th digit ratio, sexual dimorphism, population differences, and reproductive success. evidence for sexually antagonistic genes?

ABSTRACT

The ratio between the length of the 2nd and 4th digit (2D4D) is sexually dimorphic, with mean male 2D4D lower than mean female 2D4D. It recently was suggested that 2D4D is negatively correlated with prenatal testosterone and positively correlated with prenatal estrogen. It is argued that high prenatal testosterone and low estrogen (indicated by low 2D4D) favors the male fetus and low prenatal testosterone and high estrogen (indicated by high 2D4D) favors the female fetus. The patterns of expression of 2D4D are interpreted in terms of sexually antagonistic genes.We report data on the following. (a) reproductive success and 2D4D from England, Germany, Spain, Hungary (ethnic Hungarians and Gypsy subjects), Poland, and Jamaica (women only). Significant negative associations were found between 2D4D in men and reproductive success in the English and Spanish samples and significant positive relationships between 2D4D in women and reproductive success in the English, German, and Hungarian samples. The English sample also showed that married women had higher 2D4D ratios than unmarried women, suggesting male choice for a correlate of high ratio in women, and that a female 2D4D ratio greater than male 2D4D predicted high reproductive success within couples. Comparison of 2D4D ratios of 62 fatherchild pairs gave a significant positive relationship. This suggested that genes inherited from the father had some influence on the formation of the 2D4D ratio. Waisthip ratio in a sample of English and Jamaican women was negatively related to 2D4D. (b) Sex and population differences in mean 2D4D in samples from England, Germany, Spain, Hungary (including ethnic Hungarians and Gypsy subjects), Poland, Jamaica, Finland, and South Africa (a Zulu sample). Significant sex and population differences in mean 2D4D were apparent.