344 AN INTRODUCTION TO MODERN GENETICS 



unjustified. Not only are nations not necessarily races, but we know 

 very little about the mental differences which presumably exist between 

 different racial groups. 



A few attempts have been made to investigate such differences and 

 evaluate them in genetical terms. American negroes, for instance, 

 nearly always give lower average I.Q. scores than whites, from whom 

 they differ "racially" as well as culturally,^ Typically, the average negro 

 I.Q. is about 75-80 per cent of that of the whites. But there is con- 

 siderable overlap when individuals are considered, and about 25 per 

 cent of negroes equal or surpass the white average. The genetic signifi- 

 cance of the results is very difficult to assess. Unfavourable environ- 

 ment certainly plays some part in lowering the negro attainment; thus 

 negroes from northern states score better than those from the poorer 

 southern states, and when the negroes and whites live imder approxi- 

 mately the same conditions, as in the small island near Jamaica investi- 

 gated by Davenport and Steggerda,^ their average scores are more 

 nearly the same (but in the former case there may have been some 

 selection of better negroes in the northern states and in the latter of 

 poorer whites to five on the island). Tests on negro infants of 2-11 

 months, on whom the external environment has not had much time to 

 act, show that they also score slightly lower than white infants in the 

 so-called Baby Tests, but the difference is not so large as when adults 

 are compared. Even at this age, the negro children are somewhat 

 inferior to the whites in physical development, so that it is probable 

 that their environment, including pre-natal environment, had been 

 inferior. There is as yet no way of telling whether these environmental 

 effects can account for the whole difference between whites and negroes; 

 it is perhaps rather unlikely that they can. It must be remembered, 

 however, that the I.Q. tests do not measure aU aspects of personality, 

 and there may be other respects in which negroes surpass whites. 



A large-scale investigation of natio-racial differences was made at 

 the time conscription was introduced in the United States in 19 17. 

 Brigham^ found that most immigrant peoples, except those from nor- 

 thern Europe, made lower average scores than native-bom Americans. 

 But the scores of Americans from different states were quite highly 

 correlated with the expenditure of the state on education, and there 

 was also a high correlation between the national scores and the rating 

 of the educational facilities provided in the coimtries of origin. It 



^ Rev. Freeman 1934. 



^ Davenport and Steggerda 1929. ^ Brigham 1922. 



