158 ORTHOGENETIC EVOLUTION IN PIGEONS. 



unit-characters to those first organized. Furthermore, these unit-characters are 

 held to be essentially unchangeable, and hence the species compounded of them are 

 viewed also as essentially immutable. A unit-character, it is true, may undergo 

 transmutation — i.e., it may become a wholly new unit-character. Such transmu- 

 tation, however, is always sudden, never by slow, intermediate degrees. Any slow 

 and gradual transition, such as Darwin and Wallace maintained, never, under any 

 circumstances, according to de Vries, could lead to the formation of a new species. 

 The utmost that could be attained by such variation would be only an improved 

 race — i.e., merely a better variety of the same species, a variety that remains better 

 only so long as cultivated under favorable conditions, reverting to the common 

 level as soon as left to itself under normal conditions. 2 

 The fundamentals in the mutation-theory, then, are: 



(1) Every species consists of a fixed number of unit-characters. 



(2) The species and the component units are alike sudden in origin and unchang- 

 ing in type. 



(3) Old characters may be suddenly transmuted into new ones, but between 

 the two there is always a gulf of absolute discontinuity, with no possible bridge of 

 gradual modification. 



(4) Continuous intergradations may connect a species with an improved race, 

 but never one species with another species. 



(5) Species-formation is kaleidoscopic — i.e., chance-wise in direction — never re- 

 sulting from a tendency to vary in any one determinate direction. 



(6) Natural selection can not give origin to new species; it can only weed out 

 from those already in existence such as are incapable of sustaining themselves. 



Of these fundamentals, that of "unit-characters" is the pivot on which all the 

 others revolve. This conception implies that every character of the adult organism 

 preexists in some rudimentary form in the germ-cell from which the organism 

 develops. These assumed unit-characters must be as fixed in number and constitu- 

 tion in the fertilized egg as in the adult. Moreover, unless we assume that these 

 units may mutate at any stage of development, we must suppose that all mutations 

 destined to appear in adult stages must originate in the very first stage of existence 

 of the primordial units. Thus mutation would be carried back to the "pre- 

 mutation" not easily reached by investigation. Such conceptions help us in no 

 wise to understand the origin of species. To claim that we can actually see muta- 

 tion performed is the climax of absurdity. 



De Vries has seen offspring differing more or less constantly from the mother 

 plants. These visible differences are referred to invisible differences in one or more 

 of the invisible unit-characters conjectured to exist in the seed before germination. 

 The initial differences, in which, ex hypothesi, the whole mutation is given, de Vries 

 has never seen and probably never expects to see. If there be any such thing as 

 mutation, as conceived by de Vries, it is safely beyond human ken, and it remains 

 to be seen if it be approachable through experimental investigation. 



This theory of mutation coincides well with Batcson's doctrine of "disconti- 

 nuity." Discontinuity in evolution has all the elusiveness of mutation. The dis- 

 covery of such a negative is tantamount to a failure to discover anything just where 

 the instantia crucis is most manifest. A new form appears; it differs in one or more 



'Several quotations from de Vries at this and other points are omitted. — Ed. 



