Homo sapiens are bilaterally symmetrical but not with toe length and toe-length ratios among Nigerians

Abstract

The concept of bilateral symmetry in organisms involves the division of the body plan along a plane that splits the animal's body into right and left sides that are mirror images of each other. However can this be true for toe lengths and ratios? The present study evaluates the symmetric differences in toe length and toe-length ratios among the three major ethnic groups in Nigeria. A total of 1574 adult Nigerian Hausas (664), Igbos (420) and Yorubas (490) of equal sex were included in the study. Aged between 18-65 years, were randomly selected from various states. Written informed consent was taken from each participant, sample size was determined by proportion, using Cochran formulae for infinite population. A digital Vernier caliper was used to obtain direct linear measurements of the toe length of both feet; hallux (1T), second toe (2T), third toe (3T), fourth toe (4T), and the fifth toe (5T). Ten (10) possible toe-length ratios were also determined and named as follows; 1T/2T, 1T/3T, 1T/4T, 1T/5T, 2T/3T, 2T/4T, 2T/5T, 3T/4T, 3T/5T, and 4T/5T. Data were analyzed using SPSS (IBM^®Armonk, New York, USA) and Minitab V17 (Minitab^® Inc. State College, Pennsylvania) statistical software. Paired-sample t-test was used to evaluate symmetry; Pearson’s Correlation was used for inter-prediction of the toes and ratios. Confidence level was set at 95%; as P-values ≤0.05 were considered significant. The result showed that some of the toe length of both feet were significantly assymetrical among the studied ethnic groups; Hausa males (1T df=1.35 and 5T df=0.55; P<0.05) and females (1T and 3T; (1T df=0.27, 3T df=0.47) P<0.001), Igbo males (1T, 3T and 4T(1T df=0.47, 3T, df=-0.53, 4T df=-0.58) ; P<0.05 and females 1T and 3T(1T df=0.40, T3 df=-0.64) ; P<0.01) and Yoruba males(1T, 2T, 3T and 5T(1T df=1.29, 2T df=0.47, 3T df=0.15, and 5T df=0.55,); P<0.001) and females (1T and 5T(1T df=0.77; 5T df=0.23) ;P<0.001). The toe-length ratios also displayed symmetrical differences for Nigerian male population; 1T:2T [t=3.78, P<0.001], 1T:3T [t=6.27, P<0.001], 1T:4T [t=6.04, P<0.001], 1T:5T [t=2.43, P=0.015], 2T:3T [t=2.23, P=0.026], 3T:5T [t=-3.78, P<0.001] and 4T:5T [t=-3.77, P<0.001].For the female population, all ratios were not significantly different except for1T:4T [t=2.56, P=0.011]. However, both feet displayed significant positive association for co-estimation of the corresponding toe length and toe-length ratios (r-values ranging from 0.20-0.70 at P<0.05).Ethnic and sex specific asymmetry were observed in the toe length and toe-length ratios; thus suggesting that anthropometrically, organisms are not completely bilaterally symmetrical.

Keywords: Asymmetry, Bilateral symmetry, Toe length, Toe-length ratio, Ethnic groups