INTRODUCTION 6 



is the second major feature of organic evolution and, ap- 

 parently, is controlled by a separate principle. This prin- 

 ciple operates to control the ultimate character of the 

 organisms present in any stage of the progress of evolution ; 

 in other words, it determines the retention or destruction 

 of species on the earth. The third major feature of organic 

 evolution is concerned with direction or progress. This 

 feature has been spoken of as the principle of progressive 

 evolution. Biologists are quite agreed that there is a 

 "something" directing organic evolution toward an ever 

 more complex and specialized end. There are many ex- 

 amples of individual groups (genera) of animals which do 

 not follow the general law, but exhibit regressive characters. 

 However, regressive forms are explainable exceptions, and 

 do not destroy the general principle of progressive 

 evolution. 



A great amount of confusion has existed in the ranks of the 

 evolutionists. This confusion, it appears, has been largely 

 due to a lack of proper evaluation of the cardinal features 

 involved in organic evolution. The discussions have 

 centered chiefly about Darwin's explanations. In Natural 

 Selection, Darwin has established one of the cardinal 

 principles that is operative. Natural Selection determines 

 the character of life at any period in evolution; it is the 

 principle that controls the retention or destruction of formed 

 species. Darwin, apparentlj^, recognized the insufficiency 

 of Natural Selection to produce new species and introduced 

 other factors to fill this gap in the explanation of organic 

 evolution. These subsidiary factors have not been ac- 

 ceptable to a large group of biologists. Modern writers 

 have recognized the insufficiency of Darwin's hjTDothesis 

 to explain the origin of species. The "unknown factor" 

 in organic evolution has been especially emphasized by 

 Osborne, Bateson, Kellog, and other recent writers. This 

 "unknown factor" is especially concerned with the origin 



