DARWIN'S METHOD 215 



differences between races and between conditions, he sought to ac- 

 count for the former by the latter. 1 His very learning and the skill 

 with which he used it contributed, through exhaustion of materials, 

 to render the task of his successors difficult. The actuality of 

 evolution was proved and the method of evolution demonstrated, 

 but many problems of heredity remained. A great deal of splendid 

 work was done subsequently, but it was felt that our knowledge of 

 wild plants and animals was very vague, and an impression spread 

 that laboratory methods alone were capable of supplying information 

 sufficiently exact. 



354. But, clearly, if we are able to trace precisely the changes 

 a race undergoes as a reaction to the conditions under which it 

 dwells, if we are able to establish clearly the connections between 

 causes and effects, we observe nothing less than an actual, a very 

 perfect experiment. Such an experiment, since it is conducted by 



sciences which deal with phenomena in which artificial experiments are impossible 

 (as in the case of astronomy), or in which they have a very limited range (as in 

 mental philosophy, social science, and even in physiology), induction from direct 

 experience is practised at a disadvantage in most cases equivalent to impracti- 

 cability ; from which it follows that the methods of those sciences, in order to 

 accomplish anything worthy of attainment, must be to a great extent, if not 

 principally, deductive. This is already known to be the case with the first of 

 the sciences we have mentioned, astronomy ; that it is not generally recognized 

 as true of the others is probably one of the reasons why they are not in a more 

 advanced state " (op. cit., III. vii. 3). 



1 " If what is called observation is at so great a disadvantage, compared with 

 artificial experimentation, in one department of the direct exploration of pheno- 

 mena, there is another branch in which the advantage is all on the side of the 

 former. 



" Inductive inquiry, having for its object to ascertain what causes are connected 

 with what effects, we may begin this search at either end of the road which leads 

 from one point to the other ; we may either inquire into the effects of a given cause 

 or into the causes of a given effect. The fact that light blackens chloride of silver 

 might have been discovered either by experiments on light, trying what effect 

 it would produce on various substances, or by observing that portions of the 

 chloride had repeatedly become black, and inquiring into the circumstances. 

 The effect of the urali poison might have become known either by administering 

 it to animals, or by examining how it happened that the wounds that the Indians 

 of Guiana inflict with their arrows prove so uniformly mortal. Now it is manifest 

 from the mere statement of the examples, without any theoretical discussion, 

 that artificial experimentation is applicable only to the former of these modes of 

 investigation. We can take a cause and try what it will produce ; but we cannot 

 take an effect and try what it will be produced by. We can only watch till we see 

 it produced, or are enabled to produce it by accident. 



" This would be of little importance, if it always depended on our choice from 

 which of the two ends of the sequence we would undertake our inquiries. But 

 we seldom have any option. As we can only travel from the known to the 

 unknown, we are obliged to commence at whichever end we arc best acquainted 

 with." (Op. cit., III. vii. 4.) 



