Blood groups and natural selection by genetical environment

A survey is given of a number of investigations indicating the importance in natural selection of the genetical environment of populations and individuals.In the introduction it is observed that blood group frequency patterns are very stable, even in very small populations, and appear independent of environmental factors. They appear to be race-specific, maintained by a process of natural selection which is dependent of the racial genetical composition. Indications in favour of this hypothesis are obtained from several studies carried out in populations of mixed origin:The introduction on a small scale into the populations of New Guinea of foreign elements with some S genes may result in a population with relatively high S frequencies; the frequencies of certain of the blood group genes in the mixed negroid populations of Curaçao are not in agreement with the racial compositions of the mixtures as they have been calculated from the frequencies of other blood group genes, and the same appears to be the case in the populations of the Himalayas. The marked variation of MNSsHe frequencies in Africa may perhaps be explained by a powerful selective pressure exercized by the genetical backgrounds of the various populations, as is demonstrated by the absence of some expected genotypes among male Bush Negroes in Surinam.The effects of natural selection by genetical environment can also be demonstrated by family studies:In families with elliptocytosis Rhesus segregation shows some deviation from Mendelian laws, and the ratio of elliptocytosis-positive and-negative children appears to depend on the Rh genotype of the elliptocytosis-positive parent. From blood group studies in selected pedigrees and dizygotic twins it appears that twin pairs are more often doubly concordant for both MN and Rh than is to be expected.Some implications of the observed effects of natural selection in the study of human genetics and population dynamics are briefly discussed.