Anthropometric Correlations between Adult Brothers

Abstract

ANTHROPOMETRIC measurements have been made on 32 pairs of brothers. All subjects are adult men. The average age of the younger brothers is 32.3 yr., that of older brothers, 39.4. Age differences between members of the same pair vary from 1 to 20 years. The brother–brother correlations are shown in Table 1. Some coefficients are low but, unless below 0.35, they are significant at the 5–1 per cent level. Low coefficients are to be expected because in a panmictic population a brother–brother correlation should not significantly exceed 0.50 (or 0.42 for autosomal dominant characters). Other coefficients are higher but, as for low significant correlations, with two exceptions there is no significant departure from 0.50. For head breadth and cephalic index, correlations are surprisingly high and significantly above 0.50. Such values can be expected if, instead of random mating, there is a fairly high degree of homogamy. In man, assortative mating exists primarily for body-height, secondarily for some characters correlated with stature. In our sample, fraternal correlation for body-height is low and does not differ significantly from 0.50, the limiting value compatible with panmixia. One can guess that assortative mating is directly related to some other anatomical traits, but it is hard to believe that cephalic index, which gives the strongest correlation, can be sexually attractive. A quite different explanation seems to be more credible.