ASPECTS OF KINETIC EVOLUTION 3OI 



tion, selection pertaining not to the characters themselves, but 

 to the determinants which might repeat the characters in the 

 next generation. Further elaboration of the doctrine of deter- 

 minants has been made in the belief that the external conditions, 

 while unable to act through the body of the organisms, might 

 act directly upon the reproductive cells. Others assume con- 

 flicts or struggles between determinants (germinal selection) as 

 possible factors in evolutionary motion. 



As a suggestion that evolution might be the result of external 

 influences, and as a means whereby characters imposed by the 

 environment could be transmitted, Darwin invented the theory 

 of pangenesis, to the effect that the germinal material carrying 

 reproductive influences was assembled from all parts of the body 

 of the parent organism. Direct evidence for this supposition 

 has never been found ; indeed, the contrary proposition, that 

 acquired characters are not and cannot be inherited, has com- 

 manded the belief of Professor Weismann and his numerous 

 followers. Having cut loose, as it were, from environment, 

 which had been the chief resource of static theories, they have 

 sought the explanation of the evolutionary problem in a so-called 

 " hereditary mechanism," by which the characters of successive 

 generations are held to be predetermined in the reproductive 

 cells. The structure of the living cell has accordingly received 

 the attention of many earnest investigators and a new science of 

 cytology has been rapidly built up. But, as in the pursuit of 

 her somewhat older sister, embryology, no general uniformity 

 of structure or processes has been discovered. Biology has 

 been enriched by the addition of a vast number of interesting 

 facts, but the minute structure and internal organs of plants and 

 animals, including the structure and organs of the component 

 cells themselves, have been found to share the general diversity 

 of nature, and to be as much in need of evolutionary explana- 

 tion as the external characteristics of the various natural groups. 



With an infinity of biological facts to draw upon, no theory 

 need remain without support, real or apparent. An evolu- 

 tionary inference warranted in one group may be quite false as 

 a general law, and in this sense an inadequate theory may be 

 more misleading than one which is actually erroneous. Thus 



