Differential sexual dimorphism in bone diameters of subjects of European and African ancestry.

The 1,589 low-income adult subjects of primarily African ancestry (American Negroes or “Blacks”) showed systematically less sexual dimorphism in total subperiosteal area (TA), medullary area (MA) and cortical area (CA) than did 4,379 low-income adult subjects of European derivation (“Whites”). These systematic findings have implications both to the sexing of skeletal remains from diverse populations and to an understanding of population divergences in bone remodeling. While sexual dimorphism in many body lengths is comparatively small, averaging 6-7% for adult stature, percent sexual dimorphism is much greater for some bony dimensions, for many tissue masses (including the skeletal mass) and for bone volumes as variously measured. By way of example, sexual dimorphism in skeletal weight is of the order of 33%, and percent sexual dimorphism in the total subperiosteal area or “bone envelope size” of the second metacarpal comes close to 40% (cf. Garn, ’70). The question is whether this degree of sexual dimorphism, as ascertained for living, well-nourished contemporary American-born adults of European ancestry applies to other populations or when the conditions of life are somewhat different. To answer this question, we have extended our previous radiogrammetric studies of the hand skeleton to an additional 5,968 adult subjects between the ages of 20 and 55, from nine states (California, Kentucky, Massachusetts, Michigan, New York, South Carolina, Washington, West Virginia and Texas). Of the total number, 4,379 were of European derivation (designated as “Whites” in the Multi-State Survey of 1968-70) and 1,589 were of largely-African ancestry, designated as “Blacks,” and confirmed by the high frequency of triquetral-lunate fusion (Garn et al., ’71). Both groups were generally of low income and with individual incomeneeds ratios largely below 2.0, using the Orshansky index (Orshansky, ’65). Measurements on the postero-anterior hand radiographs included the total subperiosteal diameter (T) and the medullary cavity width (M), as described in Garn (‘70). The bone areas were computercalculated to provide the total subperiosteal area (TA), the medullary cavity area (MA) and the cortical area (CA) as described in Garn (’70) and Garn, Poznanski and Nagy (‘71) and our earlier publications. Percent sexual dimorphism was calculated, for each decade grouping as : loo( , M -1.0) In the initial steps of the data comparison, percent sexual dimorphism was separately expressed for both American White and American Negro participants, for each of four decade groupings, and for each of the three metacarpal areas described above. However, the differences were sufficiently systematic, in all 12 agerace comparisons to justify pooling of the data as in table 1. Simply to summarize the table, per cent sexual dimorphism in metacarpal areas was greater in the subjects of European ancestry. It was 37% for total subperiosteal area (TA) in the 4,379 subjects of European derivation and 30% in those of largely-African ancestry. The area of the medullary cavity (MA) was even more di127 AM. J. PHYS. ANTHROP., 37: 127-130. 128 S. M, GARN, J . M. NAGY A N D S. T. SANDUSKY