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COOK 



acquired from the environment are those which contribute in a 

 definite manner to evolution. The kinetic interpretation en- 

 ables us to understand the probability that a character is pre- 

 served for the same reason for which it appears in the first 

 place. 



The name Darwinism is commonly, though rather unjustly, 

 limited to the gradual or selective theory under which variations 

 gained genetic significance only when they were favored by 

 partial or complete isolation, brought about either by the elim- 

 ination of the less efficient parental form during the struggle for 

 existence, or through geographical or other accidents prevent- 

 ing the swamping effects of intercrossing. This meant that 

 variations did not tend to be preserved, that they tended only 

 to continue their fluctuations around the stationary specific 

 average. This conception was based, as already indicated, on 

 the choice of the fluctuating variations or unspecialized het- 

 erism and artism as representing the variations on which evolu- 

 tion proceeds. 



Under the assumption that organisms are normally stationary 

 it was natural to ascribe variations to new conditions. It may 

 be found, however, that the facts can be accommodated as well 

 or better by supposing that new conditions of nutrition and 

 growth afford more facilities for variation. Variations, once 

 produced, tend to repeat themselves ; not, it may be, in all of the 

 offspring, but at least in some of them. The object of varia- 

 tions, the value of variations for the species, lies not so much in 

 giving them new characters as in giving them a diversity of 

 characters. Variations which appear in a part of the offspring, 

 but not in all, serve most efficiently the purposes of increasing 

 and maintaining heterism, and of insuring diversity of descent, 

 after the manner of the many secondary sexual characters which 

 appear to be quite useless except for this physiological purpose. 



The kinetic theory differs from all its predecessors in recog- 

 nizing physiological reasons for holding that new characters 

 are prepotent. From the fact that they afford opportunity for 

 organic readjustment, they enjoy an advantage over the un- 

 modified type both in accentuation of characters and in vitality 

 and fecundity of offspring. The evolutionary possibilities of a 



