356 GENERAL ZOOLOGY 



It does not seem probable that we shall ever again have 

 to renew the old contest between evolution and special 

 creation. 



"But this is not enough. We can never remain satisfied 

 with a negative conclusion of this kind. We must find out 

 what natural causes bring about variations in animals and 

 plants; we must also find out what kinds of variation are 

 inherited, and how they are inherited. If the circumstan- 

 tial evidence for qrganic evolution, furnished by comparative 

 anatomy, embryology and palaeontology is cogent, we 

 should be able to observe evolution going on at the present 

 time, i.e., we should be able to observe the occurrence of 

 variations and their transmission. This has actually been 

 done by the geneticist in the study of mutations and Men- 

 delian heredity." 



Delage and Goldsmith in their "Theories of Evolution" 

 (1913) make the following statements: 



"Two important phenomena mark the evolution of the 

 organic world; one is the appearance of the different species, 

 the differentiation of the various groups recognized in the 

 classification of animals and plants, the increasing com- 

 plexity of organisms, their evolution from the lowest to the 

 highest forms; the other is the adaptation of living things to 

 the conditions and necessities of their environment. The 

 two processes, while simultaneous, differ entirely in their 

 natures and are never superimposed." 



Delage and Goldsmith are supporters of Lamarck's 

 theory and therefore attach special importance to the trans- 

 mission of characters acquired through environmental in- 

 fluences. Morgan may be looked upon as the most recent 

 supporter of the natural selection theory, though his defini- 

 tion of "selection" is different from that given by Darwin. 

 To the Lamarckian, adaptation to environment is of equal 

 importance with evolution; to the selectionist, adaptation is 

 the natural result of evolution. There is no question that 

 animals have followed certain more or less arbitrary lines 

 during their evolution on account of the inflexibility of 



