ABSTRACT

Digit ratio (2D:4D) is a sexually dimorphic trait, with females having a higher 2D:4D than males. This digit ratio has been associated with numerous behavioural traits and health conditions related to sex hormones. Four hundred and twelve secondary school students (209 males and 203 females) aged 12 to 20 years attending secondary schools within Enugu metropolis, in Enugu state, Nigeria participated in this work after an informed consent was obtained from them and their parents. Detailed information required from subjects was obtained through a standard designed questionnaire. Body fat percentage, weight (kg), Finger length (cm), height (cm), chest, waist and hip circumferences (cm) were measured using standard protocols. Body mass index (BMI), Waist to chest ratio (WCR) and Waist to hip ratio (WHR) were calculated. Blood sample for the estimation of testosterone was also obtained. The variables were studied according to sex and age groups. The data obtained was subjected to statistical analysis using SigmaStat 2.0 for Windows (San Rafael, CA) and statistical values were acceptable at p<0.05. Testosterone and all the anthropometric variables considered in this studyshowed statistical significant difference (p<0.001 and 0.002) between males and females. The result also indicated a negative significant relationship between 2D:4D of both hands and testosterone in males, while in females testosterone had a positive correlation with 2D:4D of the right hand and a negative correlation 2D:4D of the left hand (p<0.05). 2D:4D of both hands had a negative correlation with weight and height in females (p<0.01 and p<0.05) respectively while in males, 2D:4D did not correlate with height and weight (p>0.05). Males had a significant relationship with weight, height, body fat percentage and chest circumference (p<0.01) while in females testosterone had a significant relationship with weight, body mass index, body fat percentage, waist to hip ratio, chest, waist and hip circumference (p<0.05). In conclusion, the present study confirmed the existence of sexual dimorphism of finger lengths and digit ratios as well as in body composition variables. It also showed a relation between digit ratios and testosterone in the adolescent age group. These findings could be of importance in addressing biological traits and health conditions related to sex hormones.

BACKGROUND

There are very few parts of the human body in health or disease that provide observation better than the hand. The hand presents excellent opportunities for us, students of human nature and of human anatomy to exercise power of observation and to study the outward form of a portion of the body (Jones, 1942). But more to our purpose is the fact that in probing deeper into the anatomy of the hand we are immediately brought face to face with some of the most important biological problems and some of the most striking exhibitions of general vital principles. The fingers in the adult human hand differ in length and in distal extent (Jones, 1942). These finger lengths are fixed for life within the first three months of pregnancy (Manning et al., 1998;Csathoet al., 2003). Contemporary anthropological studies have found that in the clear majority of males, the distal extent of the ring finger tends to be relatively greater (using the middle finger as standard) than the index finger (Manning et al., 1998; McFadden and Shubel, 2002). However, the results for females vary considerably with some studies reporting that females show a similar pattern to that of males (Manning et al., 1998) while others suggest that the prevalence of a longer index finger is relatively or absolutely more common in females (Danborno et al.,2008a). This shows that the ratio of the index finger (2D) to that of the ring finger (4D) in humans is sexually dimorphic (Ecker, 1875; George, 1930; Phelps, 1952; Manning, 2002). This sexual dimorphic trait is also found in bonoboos (Ecker, 1875; Jones, 1942; Manning et al; 2003; Danborno et al., 2008a). Finger length ratio is historical to what went on in the womb at the time when the brain, heart and other organs were growing (Malaset al., 2005; Mclntye, 2005 and Danbornoet al., 2008b). It suggests that a relatively long ring finger is a sign that certain organs were exposed to higher levels of testosterone while a relatively long index finger points to lower level of male hormone and higher levels of oestrogen (Manning et al., 2003 and Danborno et al., 2008a).