440 TJie Doctrine of Evolution. 



intimately related one with another, and that all may be 

 brought under contribution in illustrating the history of 

 cosmical events. Thus, in one way and another, about the 

 time when Mr. Darwin set out on his memorable voyage 

 around the world, men were beginning to arrive at a vague 

 general conception of evolution as an orderly succession of 

 phases of nature, in which any given phase is produced from 

 an antecedent phase through the agency of causes which are 

 like those now in operation, and which must therefore ad- 

 mit of definite scientific study and explanation. 



The time had at length arrived when the facts of organic 

 life could be brought under this general conception. As 

 long as it was supposed that each geologic period was sepa- 

 rated from the periods immediately before and after it by 

 Titanic convulsions which revolutionized the face of the 

 globe, it was possible for men to acquiesce in the supposi- 

 tion that these convulsions wrought an abrupt and whole- 

 sale destruction of organic life, and that the lost forms were 

 replaced by an equally abrupt and wholesale supernatural ' 

 creation of new forms at the beginning of each new period. 

 But as people ceased to believe in the convulsions, such an 

 explanation began to seem very improbable, and it was com- 

 pletely discredited by the fact that many kinds of plants 

 and animals have persisted with little or no change during 

 several successive periods, side by side with other kinds in 

 which there has been extensive variation and extinction. It 

 was further observed that between the forms of successive 

 periods in the same geographical regions there was a mani- 

 fest family likeness, indicating that the later were connected 

 with the earlier through the ordinary bonds of physical de- 

 scent. A host of facts from comparative morphology and 

 embryology went to confirm this inference ; and so, when 

 after nearly twenty years of incubation Mr. Darwin was 

 ready to plant the seeds of his remarkable theory, he found 

 the soil very thoroughly prepared and fertilized in which to 

 plant them. All that men were waiting for was the discov- 

 ery of a vera causa. All that was wanted was to be able to 

 point to some one agency, similar to agencies now in opera- 

 tion and therefore intelligible, which could be proved to be 

 capable of making specific changes in plants and animals. 

 Mr. Darwin's solution of the problem was so beautiful, it has 

 become so generally accepted and so deeply interfused into 

 all the thinking of our time, it seems now so natural and so 

 inevitable, that we may be in danger of forgetting that the 



