148 



The theories may be grouped as pre-Darwinian, Darwinian and 

 post-Darwinian. 



(<?) Pre-Darwinian. (Chiefly static.) 



1. The environment (many of the factors of which are known) 

 directly causes organisms to change. (Lamarck, de Maillet, 

 NageH, and others.) 



2. The inheritance of the effects of use and disuse is a causal 

 factor in the change. (Lamarck, Spencer.) 



(d) Darwinian. (Partly static.) 



The changes of variation (howe\'er caused) are of the kind 

 known as continuous. Certain of these changes are perpetuated 

 by natural, /. t., environmental, selection. The fittest only sur- 

 vive. (Darwin, Wallace.) There have been several modifica- 

 tions of Darwinism as originally proposed by Darwin. Darwm, 

 and especially Huxley, recognized the fact that variations might 

 be spontaneous (kinetic). 



{c) Post-Darwinian. 



1. The variations of evolutionary significance are spontaneous 

 (kinetic), and discontinuous (mutations). One method of evolu- 

 tionary ad\-ance is by the operation of natural selection on 

 mutations. Hybridization is also a factor. (De Vries.) 



2. The variations involved in evolution are continuous and 

 spontaneous (kinetic), resulting entirely from interbreeding {sym- 

 basis). Natural selection is not a factor in evolution. (O. F. 

 Cook.) 



This last hypothesis is most fully elaborated in " Aspects of 

 Kinetic Evolution." According to the author, " The kinetic 

 theory of evolution finds in the facts of organic development in- 

 dications that the characters of species change spontaneously, or 

 without environmental causation (p. 197), and holds "that evo- 

 lution arises from the association of organisms into interbreeding 

 groups, or species" (p. 290). 



Evolution, "the process of change by which the members of 

 an organic group become different from their predecessors, or 

 from other groups of common origin" (p. 277), differs from spe- 

 ciation, or " the attainment of differential characters by segregated 

 groups of organisms, that is, by subdivision of older species (p. 



