Problems and Concepts of Evolution 23. 



and it seems to me that that " phyletic type " is nothing more than a chance 

 association of gametic factors, such that it is disrupted with extreme difficulty, 

 but which has also great capacity for adjustment to meet widely varying con- 

 ditions of existence, capacity for slight added changes, and nothing more. If 

 this is true, then it is to be expected that at some future time it will be possible 

 to dissociate the various factors productive of a phyletic type and perhaps 

 change the phyletic type experimentally. This may be something which will 

 not be accomplished for a long time, but it is not unthinkable that it may be 

 accomplished at any moment with the methods now available. Likewise from 

 the same basis of factorial composition long trends of evolution which one finds 

 are but the potentialities present in these types for the continued successful 

 addition, reconstruction, and rearrangement within localized or trivial portions 

 of the original factorial composition of the race. This view finds more or less 

 of confirmation in the expressed opinion frequently given by paleontologists 

 that evolution after all consists merely in the specialization or in the reduction 

 of the characters of the original progenitors of the group, and this conception 

 does account for and provide us with an experimental basis from which to 

 investigate the condition characterized as orthogenetic. 



In physical operations, given a specific composition and conditions in the 

 medium, a given cause wiU produce a reaction only in one direction, and this 

 reaction will follow through a definite predetermined series of steps which are 

 entirely due to the relations existing between the factors of composition within 

 the mass and the process of decomposition, rearrangement, and loss of factors, 

 and it is probable that the orthogenetic sequences where they exist at all are due 

 entirely to this cause, which is purely naturalistic and is capable of exact 

 experimental production and investigation. 



The factorial conception is certain to prove the most usable working hypoth- 

 esis available at the present time. No doubt its formulation at the present 

 moment, and our description of the factors and the designation of them, are in 

 crude terms a pragmatic personification, but it is recognized that these are at 

 present only symbolizations ; nevertheless there can be no reason to doubt the 

 existence of these factors and the type of their reactions in the gamete, which 

 are characterized as germinal factors, any more than to doubt that there exists 

 in the mediimi various physical agents which are external factors in evolution 

 operations. 



