INTRODUCTIONPhysical characters like measurements of head and face, colour of skin, form of hair, etc., have been a basis of racial classification for over a century. This classification, with the help of information fiom historical, archaeological, linguistic and other fields, has enabled a building up of the story of early migrations of man on the earth's surface.Hirszfeld I% Hirszfeld (1 9 19) introduced the distribution of human blood groups as a new basis of classification. An enormous mass of information haa accumulated since then on the distribution of ABO blood groups. Distribution of other genetical characters like taste reactions to phenylthiocarbamide (P.T.c.), the later discovered blood groups, eta, are a h being studied gradually.The use of genetical characters offers a special advantage over the physical characters for understanding the dynamics of human populations. Wright (1937) has derived mathematical expressions for the immediate factors that tend to cause systematic changes in gene frequency. These factors are: (a) mutation pressure, (6) immigration pressure, (c) selection pressure and (d) the random variations, due to accidents of sampling. The most important factor for van'.cltions in gene frequency of the human genetical characters discovered 80 far seems to be the random variations due to accidents of sampling. This factor, according to Wright, would demand a knowledge of the genetically effective population size ' N '. Wahlund (1928) and Dahlberg (1929) pointed out much earlier that the number of individuala among whom a person may c h o w his or her mate is limited by several factors. This number measures an 'isolate', a concept related to Wright's concept of ' N ' . Dahlberg (1938) and Dunn (1947) have attempted to estimate the average size of isolates by studying the frequency of consanguineous marriages in a population.
THEPROBLEMPeople of India* are almost under an experimental environment, broken up into a large number of mutually exclusive groups, whose members are forbidden, by an inexorable social hw, to marry outside their own group. The origin and evolution of a large majority of these groups are lost in a distant past which critical history cannot trace. Some of these groups have remained socially isolated for a hundred generations or more.The purpose of this paper is to present the distribution of genetical characters of some selected endogamous groups. Only those groups are selected whose physical characters were studied previously by others, and conclusions have been arrived at aa to their racial composition. It is intended to compare their conclusions based on physical measurements with the results of the present study bamd on genetical characters.During the course of the present investigation ABO, A,A, , M N and Rh blood groups, taste reactions to P.T.C. and colour blindness of the red-green type were studied for six endogamous Throughout this paper, the word 'India' connotea the whole of the Indian subcontinent 88 before its political pertition in August 1947. L. D....
