216 SUMMARY 



nature under natural conditions, spreads over a great number of 

 generations, includes the largest possible number of families and 

 individuals, and results eventually in definite and unmistakable 

 changes of considerable magnitude, is superior to any inquiry that 

 can be devised in the laboratory, where only a very few generations 

 can be studied, and where, since our power of observing and 

 measuring the lesser variations is very limited, it is impossible to 

 observe gradual but cumulative change. Provided the conditions 

 of accurate observation are present, I think no thoughtful biologist 

 would maintain that the method of comparing races is scientifically 

 unsound. He might insist, however, that such conditions are never 

 met. Undoubtedly they are difficult or impossible to find when 

 we study natural species of plants and lower animals, and the 

 study of domestic varieties is misleading. But one vast field of 

 research has been left practically untilled by students of heredity 

 the human species. Here, if only because we are very familiar 

 with the subjects of observation and, therefore, able to note small 

 differences, our knowledge is more definite and precise than in the 

 case of any other species. In certain particulars at least we are 

 able to watch, under conditions insuring great accuracy, the 

 tremendous and crucial experiments made by nature. 1 We may 

 see the differentiation of races occurring in such a way as enables 

 us to trace the connexion between cause and effect. In a real sense 

 we may extend our observations over hundreds of generations and 

 thousands of years, for, in many instances, by comparing con- 

 temporary races, we are able to ascertain exactly the ancestral 

 type of a race that has changed under the influence of a precisely 

 known agent. 



355. Occasionally I have expressed myself very positively in 

 the preceding pages, and this will be displeasing to some readers. 

 But the evidence on which my conclusions are founded is given in 

 detail, and certitude is not necessarily dogmatic nor unscientific. I 

 have tried, as best I am able, to test my thinking. I can only ask 

 my readers, while bearing the evidence in mind, to think out the 

 greater problems of heredity for themselves to ask themselves 

 whether evolution is ever anything but adaptation, whether it is 

 possible for any class of characters to be in any true sense more 

 innate or inheritable than any other, whether it is conceivable that 

 the development of the individual can occur otherwise than by 

 recapitulation, and therefore, whether retrogression can ever be 

 other than reversion, whether the main mass of retrogression is 



1 See footnote, 53. 



