THE HUMAN SPECIES 511 



group AB has the genotype AB. From these data the frequencies of the genes 

 0, A, and B can be calculated for any population in which the phenotypic fre- 

 quencies are known. 



It turns out that gene B is high in the populations of interior and southwestern 

 Asia and declines in all directions away from that center, being low in Europe 

 and apparently absent in Australian natives and American Indians. Gene A, on 

 the contrary, occurs all over the world, varying sharply from region to region and 

 sometimes from tribe to tribe. The recessive gene is, of course, everywhere 

 present in inverse ratio to the combined proportion of A and B. Boyd analyzed 

 in similar fashion the distribution of gene frequencies for the subgroups of gene 

 A, and for the MN and Rh series of alleles. 



On the basis of the blood-group genes, bolstered by what little is 

 known of the genetics of other traits, Boyd divides mankind into six great 

 races: (1) Hypothetical Early European; (2) European or Caucasoid; 

 (3) African or Negroid; (4) Asiatic or Mongoloid; (5) American Indian; 

 and (6) Australian. Considering his devastating and sometimes caustic 

 critique of the older morphological approach to race study, it is inter- 

 esting to see how closely his racial divisions conform to those of earlier 

 classifications. 



Phenotypic traits and measurements. It will probably be a long time 

 before we know enough about human genetics to be able to discuss racial 

 classification solely in terms of gene frequencies. In the meantime we have 

 the evidence of our eyes and of our measuring instruments to guide us. 

 The traits in which men differ are the phenotypic expressions of genetic 

 factors. This means that many traits must include a variable and undeter- 

 mined environmental response, that we may often confuse similar pheno- 

 typic effects of different genes, and that we can deal only with differences 

 that are visible or measurable. In spite of these limitations it seems 

 evident that heredity must be the preponderant factor responsible for 

 the observable differences between men; the agreement between geneti- 

 cally based and morphologically based classifications supports this 

 conclusion. 



The traits with which we deal are relatively trivial differences, relating 

 to the skin and its appendages and to the proportions of the body and its 

 parts. Such things as hair form, coloration, variations in facial features, 

 and stature are apparent to the eye and together with cultural charac- 

 teristics are the basis for the easy judgements we all tend to make about 

 the race of individuals we encounter. (It would not be so easy if we saw 

 these same people naked and clean-shaven.) Other traits are best revealed 

 by measurement of various body parts, especially those of the head or 

 skull. From these may be obtained indices expressing ratios, such as width 

 to length of head, length of forearm to that of arm, and the like. By ob- 

 servation and measurement of numerically large samples of populations 



