Geometric Morphometric Analyses of Facial Shape in Twins

Abstract

Twin pairs represent a unique window into the role of heredity in the determination of any human trait. A primary characteristic by which humans present themselves to the external world is via the anatomy of their facial shape. Thus, facial images are becoming increasingly significant in biometrics and anthropological research. In this study, the method of geometric morphometrics such as superimposition and Procrustes fitting were used to generate facial shape variables in the form of relative warps of landmarks derived from perceived identical twins. Sixty pairs of twins participated in the study. A digital camera was used to photograph the subjects in neutral mode facing front. The shapes of the face were then summarized using a total of 39 landmark points from the face. Heritability was measured as concordance in the shapes of the face of each member of pair of twin. Specifically, correlation between the relative warp scores of the pairs of twins was used to test for heritability. Results showed that facial shapes of the twins had a moderate to highly positive correlation indicating that the landmark points established on one twin can also be observed in the other twin. Furthermore, the probability values of each correlation coefficient revealed that there is a significant linear relationship of the landmarks between twin 1 and twin 2 indicating a high degree of heritability of facial shapes. The results of the study underscore the utility of geometric morphometrics in the study of inheritance and variability of traits in organisms.