THEORIES OF EVOLUTION 141 



reaction of the adaptation upon the germ cells 

 produced in the same body. 



Many experiments bearing on Lamarckian prob- 

 lems have been made and some of their results are 

 interesting and suggestive, but they make possible 

 only one conclusion: that further investigation is 

 greatly to be desired. An excellent summary and 

 discussion of many of these experiments has been 

 published by Cunningham, ^o With laudable care 

 he notes the apparently positive results of these 

 experiments and their serious weaknesses, and 

 limits himself, an avowed Lamarckian, to the 

 position that the Lamarckian view best explains 

 evolution on a hypothetical basis. This is as much 

 as can be said. Proof is lacking, but experiments 

 have given results which point clearly to the need 

 for more searching and more conclusive experi- 

 ments in the future. 



Out of the contributions of the past we derive 

 little absolute knowledge of evolutionary processes. 

 The various theories have served a valuable pur- 

 pose in directing and stimulating scientific inquiry, 

 but they provide only a partial explanation of 

 evolution, and that on a theoretical basis at the 

 best. Together they have led to the accumulation 

 of a wealth of experimental evidence and observa- 

 tions bearing on this theoretical framework, from 

 the sum of which we may draw useful conclusions 



*° Modern Biology, 1928. 



