508 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



character are independently inherited. Similarly a particular combi- 

 nation of blood groups of different systems may be common, but again 

 a study of their inheritance will show that those of each system are 

 independently inherited. It ought, however, perhaps to be said that 

 the phenomenon of linkage, which occurs when the genes for two sets 

 of characters are at different places on the same chromosome, may 

 affect the independence of the characters when studied in individual 

 families, but, unless the linkage is extremely close, it will not affect 

 their independence as anthropological markers. 



In 1940 the very important Rh or Rhesus blood-group system was 

 added to the three already known, and in the succeeding years a 

 further seven have been discovered which are of anthropological in- 

 terest, in addition to a number of rare blood groups which have each 

 been found only in a very few individuals or families throughout the 

 world. 



OTHER HUMAN GENETICAL CHARACTERS 



Until about 1950, the genetical characters known in man nearly 

 all fell into two classes, the rare congenital diseases, of little anthropo- 

 logical interest, and the blood groups. Already a few other genetically 

 determined biochemical characters had been discovered, such as the 

 ability to secrete blood-group substances in the saliva, or to perceive 

 a bitter taste in the simple organic compound, phenylthiocarbamide. 

 Since then, however, the number of known biochemical characters 

 under genetical control has multiplied greatly and many of the sys- 

 tems involved have proved to be of considerable anthropological 

 interest. 



Without doubt the most remarkable and instructive example is that 

 of the hemoglobins. Since their population genetics are simpler and 

 more fully worked out than those of the blood groups, we shall consider 

 them somewhat fully, as a possible guide to the situations which may 

 be expected to arise in the study of the much more complex blood 

 groups, and of the other more recently discovered biochemical factors. 



By the year 1949 it had long been known that certain Negroes have 

 red blood cells which, when examined on a microscope slide under 

 a cover-slip, do not remain round but become crescentic or sickle 

 shaped. It had also been established for many years that some of 

 these persons suffer from a severe and intractable hemolytic or blood- 

 destructive anemia, and that the condition tends to be familial. In 

 that year Pauling, Itano, Singer, and Wells showed that the cells which 

 tend to form sickle shapes, or sickle-cells, carry an abnormal type 

 of hemoglobin molecule, with a higher positive electrical charge than 

 normal adult hemoglobin, and with a lower solubility in body fluids 

 in the unoxygenated state. In the healthy persons with sickle-cells 

 this type is present together with normal hemoglobin while in the 



