Original articlesThe 2nd:4th digit ratio, sexual dimorphism, population differences, and reproductive success: evidence for sexually antagonistic genes?
Section snippets
Materials and methods
The length of the 2nd and 4th digits was measured on the ventral surface of the hand from the basal crease of the digit to the tip of the digit. Vernier callipers measuring to the nearest 0.01 mm were used throughout this study. It is known that this measurement of digit length can be made with high repeatability (Manning, 1995). Subjects with injuries to the digits were not included in the study. The digit ratio was calculated by dividing the length of the 2nd digit by that of the 4th (2D:4D).
English sample
We recruited 300 subjects (117 men and 183 women) with a minimum age of 30 years from the Merseyside area. Participants were from social groups of elderly retired people and mature university students. A wide range of socioeconomic backgrounds was represented. In addition to digit measurements, participants were required to report the number and sex of their putative biological children. From the sample of 300 subjects we identified 60 couples and we recruited a further 30 (n = 90). These pairs
Study II—sex and population differences in 2D:4D
Early work on 2D:4D considered the trait as discontinously distributed into two classes, 2D < 4D and 2D > 4D, and was mainly based on measurements of subjects in the United States and Canada (for review see Phelps, 1952). In all these studies both classes are common. Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 show that in some samples (German, Hungarian, and Jamaican) the class 2D > 4D is quite rare. In order to examine this question in more detail, further samples were obtained as
Discussion
We do not argue that the 2D:4D ratio is important mechanistically or as a display trait in mate choice. Most probably it affords us a window into prenatal hormonal conditions. There is accumulating evidence for an association between gonad and digit differentiation. Testosterone and dihydroxytestosterone (DHT) are known to affect development of the epidermis and dermis of the digits. Jamison et al. (1993) found a positive association between dermatoglyphic asymmetry, which is determined in utero
Acknowledgements
We are grateful to Varpu Lindstrom and Louise Barrett for help with data collection.
References (50)
- et al.
Endocrine control of sexual differentiation in the human
- et al.
Hormone treatment during pregnancy and congenital heart defects
Lancet
(1973) - et al.
Human fertility and fitness optimisation
Ethol Sociobiol
(1988) - et al.
Is there an embryo-fetal eogenous sex steroid exposure syndrome (EFESSES)?
Fertil Steril
(1979) Fluctuating asymmetry and body weight in men and womenimplications for sexual selection
Ethol Sociobiol
(1995)- et al.
Women's waists and the sex ratio of their progenyevolutionary aspects of the ideal female body shape
J Hum Evol
(1996) - et al.
Breast asymmetry, sexual selection and human reproductive success
Ethol Sociobiol
(1995) - et al.
Congenital abnormalities and first-trimester exposure to progestagen/oestrogen
Lancet
(1976) - et al.
Body weight, waist-to-hip ratio, breast and hipsrole in judgments of female attractiveness and desirability for relationships
Ethol Sociobiol
(1995) Does breast cancer originate in utero?
Lancet
(1990)