Natural Selection in Man: The ABO(H) Blood Group System
Buettner-Janusch, John. American Anthropologist September, 1959 Vol. 61(3):437-451.
In this article Buettner-Janusch contends that natural selection is still active in today's civilized societies. While many believe that technological advancements leading to disease prevention and economic policies that, for the most part, limit starvation have diminished the role of natural selection in human evolution. Buettner-Janusch believes that polymorphic human populations imply that the forces of natural selection are still at work. "Polymorphism is the condition that exists when two or more discontinuous forms of a species share the same habitat and the frequency of the least common of them is to great to be accounted for by the effect of natural mutation"(Ford, 1940). Buettner hypothesizes that it is natural selection that supports this polymorphism. In order to support his original hypothesis, Buettner-Janusch puts forth an argument based upon studies done on the ABO(H) blood group system. The basic premise is as follows:
- There is a unique distribution in the four different blood phenotypes in every population group.
- The polymorphism is balanced. For example, it appears that individuals of phenotypes A and B are naturally eliminated at birth, while natural mechanisms eliminate the O phenotypes at later ages.
- The frequencies of the different genes appear to vary with geographical location.
He supports his claims with numerous statistics and data. One support for his argument is the apparent ABO(H) compatibility problem. Specifically, there appears to be a reduced number of A and B children among the offspring of O woman in a large set of matings which were heterospecific with respect to the ABO(H) phenotypes. Since there are more childless matings in the heterospecific group, it appears that natural selection operates against the A and B phenotypes. Another piece of research that indicates the presence of natural selection is the correlation between disease and the ABO(H) groups. There appears to be a strong relationship between phenotype O and duodenal ulceration, between phenotype A and carcinoma of the stomach, and between the secretor phenotype and resistance to rheumatic sequelae of streptococcus infections. In these two ways, Buettner-Janusch supports the existence of naturally selective processes still at work in civilized society. 
American Anthropologist Archives