438 PROGRESS OF SCIENCE IN THE CENTURY. 



process. Whether the selection theory is " all suf- 

 ficient/' as Weismann calls it, or " inadequate," as 

 Spencer says, it remains a potent theory. Given a 

 sufficiently abundant crop of variations, a persistent 

 struggle for existence, and a large draft on the bank 

 of Time, what may the selective process not ac- 

 complish ? 



But as aetiology has grown older and wiser, it has 

 begun to ask questions, the answers to which will 

 mean much progress. Thus there is a demand for 

 some serious attempt to measure the intensity of the 

 struggle in typical cases, and for evidence that the 

 absence of a particular variation in certain members 

 of the stock does really determine their elimination. 

 There are enquiries as to the frequency of discontinu- 

 ous or transilient variations — where a new character 

 is reached with apparent suddenness, for if these 

 are frequent this may lessen the claims which have 

 to be made on the selective process. It is asked 

 whether the task of elimination will not be further 

 lessened if the crop of variations is more definite and 

 less of the nature of random freaks than used to be 

 supposed. Information is wanted as to the degree 

 in which the struggle for existence is directly com- 

 petitive, or merely between the living creature and 

 its inanimate surroundings. Especially is it desired 

 that statistics be forthcoming to show how far the 

 elimination is discriminate, as when the pruner lops 

 off the less promiseful branches, or the breeder gets 

 rid of the unsuitable members of his stock, and how 

 far it is indiscriminate, as when the hastily driven 

 hoe strikes the cluster of seedlings. In other words, 

 evolutionists have awakened to the necessity of test- 

 ing natural selection in relation to actual cases. 



Isolation. — The raw materials of progress are fur- 



