ASPECTS OF KINETIC EVOLUTION 297 



refuse to support the theory which has led to their discovery, 

 but this does not render the facts of less value for practical pur- 

 poses, nor even for use in other and better theories. It is as 

 idle to condemn theories as to worship them ; it is the old 

 counsel of using and not abusing. 



Theories of evolution have been made thus far from the facts 

 of variation, the differences which exist among the members of 

 the same species. In each of the different systems it has been 

 assumed that a certain kind or group of variations represented 

 steps in the evolutionary journey. The philosophical circles of 

 doctrine have been described in different planes in accordance 

 with the selection of particular lines of samples from the multi- 

 tudinous facts of variation. 



The theory of natural selection is supported by the facts of 

 adaptation and geographical distribution. The theory of direct 

 adaptation was based on variations of accommodation, on the 

 fact that organisms are often able to adjust themselves to a con- 

 siderable range of environmental conditions. Nageli's deter- 

 minant theory was based on the fact that the plants most care- 

 fully studied by him showed tendencies of variation in definite 

 directions. The theory of mutation rests on facts of abrupt 

 modifications in the form and structure. 



The kinetic interpretation claims the consideration of believers 

 in the other doctrines because it affords a larger outlook upon 

 the facts of nature. Adaptation and mutation no longer appear 

 as unconnected or contradictory phenomena, but are completely 

 reconciled under one simple inference. 



The kinetic theory differs from its predecessors not merely 

 nor principally in dependence upon a different series of facts of 

 variation, but also in the method of combining them. It is not 

 merely a circle cut in one plane or described on one cross- 

 section of data, but considers all three dimensions of space. It 

 permits us to understand that variations are not all of the 

 same character or of the same evolutionary significance. It 

 also recognizes that as species are networks of descent and not 

 mere aggregates of similar organisms, so evolution is not merely 

 a summary or integration of variations, but is accomplished only 

 through the normal extension of the specific reticulum. 



