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The Black males of McNary, Arizona represent a socially and geographically isolated sample of an American caste of considerable historical duration, rural Black southern sawmill workers. Sociocultural, ethnohistorical and demographic data suggest that Black McNary males are considerably more “African” in genetic background than other U.S. Black American populations. The reflectometry curve of Black McNary males is virtually indistinguishable (and not significantly different) from that of West Africans studied by Harrison and Owen. Black McNary male reflectance values are considerably divergent (and significantly different) from back-crossed West European-African Fi hybrids studied by Harrison and Owen. Penrose’s size and shape statistic shows that Black McNary males and West African males diverge in the same direction and to the same degree from back-crossed West European-West African F, hybrids studied by Harrison and Owen. Environmental factors do not appear to explain these relationships adequately. Rather, it appears that Black McNary males are relatively more “African” genetically, because of the long-standing isolation of the caste from which they are derived.