70 Heredity and Environment 



found that there is a marked correlation (represented by the num- 

 ber .55 when complete correlation is I.) between tuberculous 

 parents and tuberculous children, but there is very little evidence 

 that the child is ever infected before birth. What is inherited in 

 this case is probably slight resistance to the tubercle bacillus. 

 There is evidence that almost all adult persons have been infected 

 at one time or another by this bacillus, but it has not developed 

 far in all of them because some have superior powers of resistance. 

 Such greater or smaller resistance, stronger or weaker build, is 

 inherited, and while diminished resistance is not the direct cause 

 of tuberculosis it is a predisposing cause. The same is probably 

 true of many other diseases, the immediate causes of which are 

 extrinsic, while only the more remote, or predisposing causes, 

 are hereditary. 



(d) Psychological characters appear to be inherited in the 

 same way that anatomical and physiological traits are ; indeed all 

 that has been said regarding the correlation of morphological and 

 physiological characters applies also to psychological ones. No 

 one doubts that particular instincts, aptitudes and capacities are 

 inherited among both animals and men, nor that different races 

 and species differ hereditarily in psychological characteristics. 



Certain breeds of dogs such as the mastiff, the bull dog, the ter- 

 rier, the collie and many others are characterized by peculiarities 

 of temperament, affection, intelligence and disposition. No one 

 who has much studied the subject can doubt that different human 

 races and families show characteristic differences in these same 

 respects. It is quite futile to argue that exceptional individuals 

 may be found in one race with the mental characteristics of an- 

 other race; the same could be said of different breeds of dogs, or 

 of the sizes of different races of beans or of Paramecia (Fig. 22). 

 The fact is that racial characteristics are not determined by excep- 

 tional and extreme individuals but by the average or mean quali- 

 ties of the race ; and measured in this way there is no doubt that 

 certain types of mind and disposition are characteristic of certain 

 families. 



