294 THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 



1. It is desirable but often very difficult to distinguish between fluctuations 

 which originate in heredity and those which originate in ontogeny. For example, 

 (a) certain bodily fluctuations, such as of the bones and muscles, may not be 

 due to heredity, but may be the anatomical expression of hereditary fluctuations 

 in the brain and nervous systems; for instance, the strong, active flight of the 

 bird, which generates strong muscles and large, well developed bones, may origi- 

 nate either in (a) fluctuations of those germ cells which give rise to those tissues, 

 or (6) in fluctuations of those germ cells which give rise to the nervous system. 1 



2. Environment may also exert a marked influence on ontogenic fluctuations 

 and cause them to appear as hereditary fluctuations. 



3. Marked anatomical changes produced by fluctuations in habit again may 

 find ontogenic (therefore non-inheritable) fluctuations in the anatomy. 



4. It is now questioned whether there are chromosomal or germinal fluctu- 

 ations in the true sense. 



Under characters of sudden origin, or saltations, we certainly must include 

 in part the "individual differences" of Darwin, also in part the "new characters" 

 of Darwin. These saltations have also been called "fortuitous variations," 

 "sports," "discontinuous variations" (Bateson). They are equivalent to the 

 "mutations of De Vries" but not to the "mutations of Waagen." 



The fact that these saltations are for the most part pure phenomena of 

 heredity is demonstrated by their hereditary stability. The question of the 

 fortuitous, that is, the indiscriminately adaptive and inadaptive character of 

 saltations, is a very important one. De Vries speaks of his "mutations" as 

 fortuitous in this sense and as preserved or destroyed by selection. 



4. SELECTION. 



Selection is not an active or creative factor in the sense of originating changes. 

 In the strict sense it acts upon the changes which are initiated by either environ- 

 ment, ontogeny or heredity; it conditions the outcome in survival or elimination 

 of the adjustments of internal and external relations; it thus acts as a sieve upon 

 the results of the interactions of environment, ontogeny, and heredity. Darwin s 

 own conception of the outcome can never be improved, namely, that this adapta- 

 tion or non-adaptation means success in the struggle for existence (through 

 ontogeny) and in leaving descendants (through heredity). Organisms which 

 would be eliminated under the safeguards afforded by heredity alone may be 

 saved through ontogeny, that is, through adaptability to new conditions. 



That the Darwinian sense of the word selection is the true sense is shown by 

 the misuse of the term. Under selection should not be included such processes 

 as " intra-selection " or "functional selection," which are purely ontogenic; 

 nor of "coincident selection" or "organic selection" (Morgan, Baldwin, 0sbor ^ 

 which are joint processes of ontogeny, or heredity, and of selection in the sen 



'It/ 



1 Analogy with man shows that these muscular, bony, and nervous fluctuations are no 



correlated. 



