348 



AN INTRODUCTION TO MODERN GENETICS 



tical considerations. The Left usually wish to show that the differences 

 are entirely accounted for by the educational disadvantages under 

 which the poorer classes suffer, while the Right wish to regard them as 

 solely genetic. It is difficult to see any necessity for these attitudes. If 

 there is any injustice in the present distribution of the physical or 

 mental amenities of life, that injustice is not increased by showing that 

 the servant is as good as his master, nor lessened by demonstrating that 

 we are only kicking the weaker brethren. If these considerations are 



Fig. U3. Average I.Q. of Children according to the Father's Occupation. 



Data are given from four different investigations. 



borne in mind, it should be possible to approach the question with no 

 preconceived bias, and to obtain an objective scientific judgment on it. 

 It is extremely doubtful, however, if we yet have adequate data to 

 make a final decision as to the relative importance of heredity and en- 

 vironment in producing class differences. The study of twins and of 

 exceptional families makes it likely that hereditary differences such as 

 occur in the population can easily produce effects of the right order of 

 magnitude (p. 338). But so, clearly, can the environment, whose most 

 profound effects are seen in studies of "wild boys" who have been 

 abandoned far from the haunts of man and grown up entirely on their 

 own resources.^ James the Fourth of Scotland is said to have performed 

 the experiment of isolating a young child on an island in the Firth of 

 Forth; when visited some years later he was able to speak good Hebrew. 

 Most parts of the world are less like the Garden of Eden; the wild boys 



^ Itard 1932, Squires 1927. 



