ASPECTS OF KINETIC EVOLUTION 211 



proving that all characters have arisen as useful adaptations, 

 other methods and causes of evolution must be sought. To 

 question the adequacy of selective and environmental causes is 

 to admit at least the possibility that such theories are completely 

 erroneous, for any causes which are adequate to produce and 

 develop useless characters can produce, a fortiori^ useful ones. 



There are enough adaptations to occupy many naturalists for 

 many life-times. They can, if they prefer, live and die without 

 hesitating to entertain doubts of the efficiency of enviromental 

 causation. And yet the fact will remain that the great majority 

 of the differences between related species and between the indi- 

 viduals of the same species have no environmental utility at all, 

 and are quite unlikely to have had any. This is not to be as- 

 certained by denying or affirming the theoretical utility or use- 

 lessness of a few selected characters, but by observing whole 

 orders and classes of organisms to learn the general proportions 

 between differences of characters and differences of environ- 

 mental relations, and by perceiving that the former vastly out- 

 number the latter. 



The fitness which the individuals of a species of plants can 

 attain by adjusting themselves to the special conditions is, as we 

 have seen, a kind of stepping aside, a morphological motion, 

 put forth by the organism itself as truly as are the coordinated 

 muscular acts which enable the higher animals to move 

 from place to place and thus to choose their own environ- 

 ments. A perennial plant must arrange to tolerate whatever 

 extremes of temperature, moisture, and exposure to sunlight its 

 habitat may provide. Its powers of making such adjustments 

 may be reckoned as functions of its tissues and organs in quite 

 the same sense as locomotion and sustained high temperature 

 are functions of the animal organism. The plant withstands a 

 temperature range of a hundred degrees and more, but mammals 

 and birds establish their own temperatures and keep them ad- 

 justed to tenths of degrees. It is a regular custom for many of 

 them to travel annually for thousands of miles to find congenial 

 conditions. The arctic plover is said to fly every year the whole 

 length of the continent from Greenland to Patagonia and back 

 again. 1 



' Knowlton, F. H. 1902. The Journeyings of Birds, Pop. Sci. Mon. 60 : 323. 



