Polymorphisms of red-green vision in some populations of Southern Africa

Some 5,000 schoolboys of the Khoikhoi, Negro, "Coloured," and Malay populations were screened with the Ishihara plates, and those with defective red-green vision were diagnosed with an anomaloscope. The findings are presented in terms of the six protan and deutan mutant alleles, a few large population-samples (e.g., Nama and Zulu) being characterized by absence of the allele for protanopia. The overall frequencies of mutants range from less than 1% to over 4%. No correspondence was found between these data and linguistic affinities of eight Bantu-speaking groups, nor between the frequencies of colorblindness and previously estimated proportions of San genes in these eight populations; on the other hand, a north-south cline of increasing frequences of mutants and of dichromacies among the Bantu-speakers was noted. The overall frequency of defective red-green vision among Cape Coloureds, 3.3%, is compatible with previously estimated racial composition of this population. The Malay sample is characterized by the highest frequency of protan mutants (2%), a 1:1 protan-deutan ratio, and an overall frequency of 4% of red-green defects. The study illustrates the potential value of anomaloscopic characterization of colorblindness in attempts to evaluate human evolutionary processes.