222 HUMAN DISEASES 



and negroes has a germinal origin, whereas that between English- 

 men at home and in India is merely acquired. So, also, the mental 

 difference between a naturally intelligent race and a naturally 

 dull one is not the same as that between two races, one of which 

 has been rendered more intelligent than the other by a better 

 system of mental training. By such terms as evolution, racial 

 change, progression, and retrogression we shall always in the 

 present work imply germinal change. By so doing we shall 

 follow an established biological custom, which, as a rule, is in- 

 fringed only when the writer mistakes acquirements for germinal 

 changes. It is often very difficult to disentangle the two, and the 

 attempt to do so will form a main part of our future task. 



365. Accepting for the moment, then, the hypothesis that racial 

 progression is invariably due to selection, whereas retrogression 

 results, as a rule, from cessation of selection, it is evident that, if 

 we seek to ascertain the direction in which a human race is under- 

 going germinal change, we must study the causes of death. If we 

 find that inferiority in any character results in a considerable 

 mortality, or in a diminution of the average number of offspring, 

 we may assume that in all probability the trait in question is 

 undergoing progression ; for here we have evidence that the 

 race is not yet well adapted to the environment. On the other 

 hand, total loss of utility, implying as it does cessation of selection, 

 implies also a tendency to retrogression. 



366. During the last few thousands of years man has altered his 

 environment in one very important way and in that one way only. 

 He has become increasingly civilized. Civilization implies, on the 

 one hand, protection from most of the dangers which beset wild 

 animals, and, therefore, cessation or diminished stringency of 

 selection along those lines of evolution which raised man in the 

 animal scale and ultimately made him human. On the other hand, 

 it implies a fuller command over the resources of nature, which in 

 turn implies a more abundant and regular supply of food, and that 

 again implies a more crowded and settled population. The problem 

 before us is whether this vast alteration of environment has resulted 

 in appreciable germinal change in appreciable progression or 

 retrogression. Civilized man differs in many striking ways from 

 the modern savage, and probably, therefore, from his remote 

 ancestors. Our task is to ascertain how much of this difference is 

 innate and how much due merely to a differential play of stimuli. 

 We shall study first man's physical characters, reserving mind 

 for a later section of this book. 



