Chapter *18 



RACES AND THE ORIGIN 

 OF SPECIES 



I 



'n cross-fertilizing species, differ- 

 ent individuals in a population 

 are heterozygous for different 

 genes (see Chapter 16), even though the 

 gene pool is at equilibrium with the factors 

 that cause shifts in gene frequency — namely, 

 mutation, selection, drift, and migration. In 

 other words, in reaching genetic equilibrium, 

 all the members of cross-fertilizing popula- 

 tions do not eventually become homozygotes, 

 nor do they all become heterozygotes. Such 

 populations, therefore, do not become either 

 genetically pure or uniform with the passage 

 of time. 



Although any given population is poly- 

 morphic for some genes, it is not necessarily 

 polymorphic with regard to a particular gene. 

 For example, Indians in South America are 

 almost all of O blood type, being homozy- 

 gous (//) in this respect, but have a poly- 

 morphic pool with respect to other genes. 

 Moreover, an allele, like I B , may be rare 

 or absent in one population, as in certain 

 North American Indians, and relatively fre- 

 quent in the gene pool of another population, 

 as in central Asia. Thus, populations lo- 

 cated in different parts of the world may 

 differ both in the types and frequencies of 

 alleles carried in their gene pools. For many 

 purposes it is desirable to identify a popula- 

 tion with certain gene pool characteristics as 

 a race. 



Races 



An investigator may choose to define races 

 only according to the distribution of the / /; 

 241 



gene for ABO blood type. He might define 

 populations that do or do not contain I' : 

 in their gene pool as different races. On 

 this basis there would be only two races of 

 man, the South American Indian (without 

 I 11 ) and all the other people (with l B in their 

 gene pool). 



On the other hand, an investigator may 

 decide to define races on the basis of the 

 relative frequency of i and / /; in the popula- 

 tion. The frequency of these alleles in the 

 gene pool has been determined for many 

 populations all over the world. The results 

 show that in western Europe, Iceland, Ire- 

 land, and parts of Spain, three-fourths of the 

 gene pool is i, but this frequency begins to 

 decrease as one proceeds eastwardly from 

 these regions. On the other hand, I B is most 

 frequent in central Asia and some popula- 

 tions of India but becomes gradually less and 

 less frequent as one gets farther away from 

 this center. Since the change in frequency 

 of these alleles is gradual, any attempt to 

 sharply separate people into races having 

 different gene frequencies would be arbitrary. 



In practice, therefore, the number of races 

 recognized is a matter of convenience. For 

 some purposes separating mankind into only 

 two races is adequate; for other reasons, as 

 many as two hundred have been recognized. 

 As a rule, most anthropologists recognize 

 about half a dozen basic races but may in- 

 crease the number to about thirty when con- 

 sidering finer population details. Regardless 

 of the number of races defined, however, 

 each is best characterized according to the 

 genes it contains. Since the people in a 

 population are either A, B, AB, or O in 

 blood type and intermediates do not occur, 

 no average genotype exists for the ABO 

 blood group, nor is there an average geno- 

 type for any other polymorphic gene. Be- 

 cause a population has no average genotype. 

 a race should be defined according to the 

 relative frequency of alleles contained in its 

 gene pool. Without an average genotype, 



