Testing for the presence of genetic variance in factors of face measurements of Belgian twins

Factor analysis with VARIMAX rotation was used to analyse 15 face measurements in Belgian same-sexed twins, aged 18-25 years: 39 dizygotic and 57 monozygotic male pairs and 42 dizygotic and 67 monozygotic female paris. According to Christian's model, we used the ratio of the within-mean squares of dizygotic and monozygotic pairs to test for the presence of a genetic component in the variance of the facial dimensions and of all the rotated factors were statistically significant (P less than 0.05), suggesting a genetic component in the variance. The probabilities of the F values were generally lower in males than in females. The factor analysis yielded five main factors of which three were well separated: face height, ear size and lips. The two others were breadth factors, but were less clearly defined, probably due to a bad selection of variables. A comparison of the F values of the factors with those of their contributing variables seemed to indicate that well-defined factors may better describe genetically determined structures than the original variables can.