EVOLUTION — CONKLIN 219 



found exclusively in the environment, in this conception the organ- 

 ism itself also selects or eliminates. There is no mechanistic ex- 

 planation of this property of life, but the same is true of many 

 other properties of living things. Because we cannot at present 

 explain mechanistically the properties of the organization of proto- 

 plasm and its capacities of assimilation, reproduction, and sensi- 

 tivity is no ground for denying that these properties exist, and the 

 same is true of the property of organic adaptation. But given these 

 properties, science can explain in a mechanistic, that is, in a causal 

 manner, multitudes of structures and functions and reactions that 

 have arisen in the course of evolution. 



It seems to me that recent theories of evolution have too often 

 left out of account these fundamental properties of life. Assigning 

 all evolution to externally caused mutations and to environmental 

 selection neglects the fact that the organism is itself a living, acting, 

 and reacting system. Life is not merely passive clay in the hands 

 of environment, but is active in response to stimuli ; it is not merely 

 selected by the environment but is also itself ever selecting in its 

 restless seeking for satisfaction. Macfarlane (1918) has called this 

 property of organisms " proenvironment " and has assigned to it an 

 important function in evolution. Cuenot (1911) has shown that 

 many animals seek and find by a process of trial and error those 

 environments for which they are by nature best adapted, and he calls 

 this " preadaptation." By a similar process, namely the elimination 

 of unsatisfactory responses, most of the individually acquired adap- 

 tations of organisms may be explained. Such acquired adaptations 

 as the repair of injuries, the regeneration of lost parts, acclimatiza- 

 tion to high altitudes or temperatures, neutralization of poisons, and 

 immunity to disease, which were at one time hailed as a " deathblow 

 to Darwinism ", may be explained by an extension of the Darwinian 

 principle of the elimination of the unfit to the multitudinous reac- 

 tions of organisms. 



From my earliest introduction to the science of biology I have 

 been an admirer of August Weismann. Of late it has become 

 fashionable to decry the speculations and theories of Weismann, 

 since they were not based on experiment. But no one can truthfully 

 deny that his logical deductions were a powerful stimulus to research 

 and that many of them have been confirmed in a truly remarkable 

 manner by recent work. He maintained, long before it was demon- 

 strated by genetics and cytology, that the hereditary substance 

 consists of discrete particles, his determinants, arranged in a linear 

 series in the chromosomes. His prediction that one of the matura- 

 tion divisions in the formation of the egg and sperm must lead to 

 the reduction of the chromosomes in those cells to one-half the 



