EVOLUTION TODAY 429 



tion of living matter and its properties is not an explanation of 

 life. 



Lamarckian Theories. In the work of Lamarck and his sup- 

 porters we find the only explanation of how change; occurs in 

 organisms. Lamarck's law of use and disuse and the modern 

 recognition of its principles refer the matter of organic change to 

 definite causes, viz., a definite heritage in living matter, expressing 

 itself according to stimuU received from the surrounding environ- 

 ment. If this were the whole story we might happily become 

 Lamarckians in the strictest sense, but unfortunately it merely 

 carries us into another incomplete conception. We can see change 

 taking place in individual organisms all about us from year to 

 year, sometimes in direct response to environmental conditions, 

 but we have never been able to see the change take place in a 

 species. Here we encounter the serious obstacle which has been 

 called the inheritance of acquired characters and the theory be- 

 comes even less useful than the others because it fails in a vital 

 particular and is therefore not even a partial explanation of 

 evolution. 



The existing theories of evolution are therefore of little indi- 

 vidual value as nuclei for an explanation of the process of evolution. 

 We cannot be selectionists or mutationists or Lamarckians without 

 subjecting ourselves to the limitations which accompany such 

 views, but we can recognize the value which exists in all of them 

 and avoid their limitations readily. 



What Must an Adequate Theory Explain? It is improbable 

 that an unbiased point of view can lead at once to a thorough 

 understanding of evolution, but it can at least make for progress 

 along sound lines. Two fundamental points must be met before 

 the processes of evolution can be known to us: (1) The source 

 of variations must be explained, not in terms of axiomatic occur- 

 rence as properties of living matter, but in terms of intelligible 

 forces of a more fundamental nature; (2) The perpetuation of 

 some characters in organisms from generation to generation and 

 the elimination of others must be explained by an intelligible 

 process or series of processes. The various fields of biology 

 have contributed so many sound facts to our knowledge of the 

 behaviour of organisms that it seems profitable to begin in- 

 quiry with an examination of the fundamental factors in 

 Ufa. 



