Is the Index Finger and Ring Finger Ratio (2D:4D) Reliable Predictor of Semen Quality?

The association between digit ratio (2D:4D) and overweight or obesity among Chinese children and adolescents: A cross-sectional study

BACKGROUND

The aim of this study was to analyze the relationship between 2D:4D and childhood overweight or obesity, which might indirectly show the role of prenatal hormone in childhood overweight or obesity.

METHODS

Using stratified cluster sampling approach, a school-based cross-sectional investigation was undertaken among 687 children and adolescents aged 8-15 years. Each participant's index finger (2D) and ring finger (4D) length, height, weight, testosterone, and estradiol levels were measured, and their dietary behaviors, physical and sedentary activities were also surveyed.

RESULTS

The prevalence of overweight or obesity among children and adolescents aged 8- and 12-15 years was 36.0% and 25.9%, respectively (P < 0.05). There were no associations between 2D:4D and overweight or obesity in both boys and girls (P > 0.05). However, 2D and multiplying index of digit ratio and length (MIDRL) associated directly with overweight or obesity among boys (OR (95%CI) were 1.45 (1.00, 2.14), 1.46 (1.01, 2.11), respectively), and was indirectly related to overweight or obesity by testosterone (OR were 1.30, 1.26, respectively).

CONCLUSIONS

In boys, 2D and MIDRL were directly related to overweight or obesity, and indirectly associated with overweight or obesity by testosterone, which suggested that prenatal hormone exposure might associate with overweight or obesity among boys.

Does human ejaculate quality relate to phenotypic traits?

A given man's phenotype embodies cues of his ancestral ability to effectively defend himself and his kin from harm, to survive adverse conditions, and to acquire status and mating opportunities. In this review, we explore the hypothesis that a man's phenotype also embodies cues to fertility or the probability that an ejaculate will fertilize ova. Female mate choice depends on the ability to discern the quality of a male reproductive partner through his phenotype, and male fertility may be among the traits that females have evolved to detect. A female who selects as mates males that deliver higher quality ejaculates will, on average, be more fecund than her competitors. Data on several non-human species demonstrate correlations between ejaculate quality and secondary sexual characteristics that inform female mate choice, suggesting that females may select mates in part on the basis of fertility. While the non-human literature on this topic has advanced, the human literature remains limited in scope and there is no clear consensus on appropriate methodologies or theoretical positions. We provide a comprehensive review and meta-analysis of this literature, and conclude by proposing solutions to the many issues that impede progress in the field. In the process, we hope to encourage interest and insight from investigators in other areas of human mating and reproductive biology. Am. J. Hum. Biol. 28:318-329, 2016. © 2015 Wiley Periodicals, Inc.

Second to fourth digit ratios, male genital development and reproductive health: a clinical study among fertile men and testis cancer patients

Second- to fourth-digit length ratio, 2D:4D, is a marker of testosterone level during foetal life that was found associated with sperm concentration or testosterone levels in some studies, but not in others, a difference possibly related to the way the ratio is assessed. In this study, 2D:4D was assessed in 122 men partners of pregnant women and in 71 testicular cancer patients using a new method based on direct measurements of finger lengths. In addition, we investigated the association between 2D:4D, birth weight, testicular volume, semen quality and time to pregnancy. A validation study of the method demonstrated high reliability and reproducibility. Neither digit lengths nor 2D:4D significantly differed in both groups of men. We found a significant negative association between 2D:4D and birth weight in testicular cancer patients. In fertile men, 2D:4D was associated with testicular volume (r=-0.36, p<0.001), total sperm number (r=-0.18, p=0.04) and time to pregnancy (r=0.24, p<0.02). In addition, participants with a history of epididymal cyst had a significantly higher 2D:4D than those without cysts. In conclusion, all significant findings indicate that the human male reproductive function is negatively related to 2D:4D. However, 2D:4D for testicular cancer patients does not point to a hormonal imbalance during foetal life as the common cause for developing germ-cell cancer. Such results obtained, thanks to an easy, direct and reliable method for measuring finger lengths, suggest the usefulness of this new tool in fertility studies as well as for studying men with developmental disorders of the reproductive tract.