1909.] CONKLIN— THE WORLD'S DEBT TO DARWIN. xlix 



seems wonderful simply because it is not common. Many of these 

 more uncommon adaptations have played an important part in the 

 discussions of the various theories of evolution which have been 

 advanced during the past century. As illustrations of adaptations 

 to particular conditions of life may be mentioned the fitness of 

 horses' limbs for running, those of seals for swimming, those of 

 birds for flight. Innumerable adaptations are found, also, among 

 animals and plants, for offense and defense, such as the sting of 

 the bee, the poison of serpents, the tusks, horns and armor of many 

 animals, the well-known structures and habits of the porcupine, the 

 rattlesnake, the opossum and the skunk. Again many animals, such 

 as the stick insect and the dead-leaf butterfly, are so like the objects 

 upon which they are commonly found that it is difficult to detect 

 them even when searching for them. 



The ability which many eggs, embryos and adults have of restor- 

 ing lost parts, and in general of resuming the typical form after 

 injury constitutes another class of fitness which is of the greatest 

 interest. Most remarkable also are the adaptations which certain 

 organisms show to desiccation, to extremes of temperature and to 

 various poisons. In particular the adaptations of organisms to 

 bacterial poisons and to snake venom, where every kind of poison 

 leads to the formation of a particular kind of anti-body which coun- 

 teracts the poison, are among the most surprising known. 



The list of such fitnesses it well-nigh endless and the question 

 of their origin forms one of the most striking and fundamental 

 problems of biology. How have lowly organisms learned to utilize 

 processes of chemistry and physics so subtle that intelligent man 

 only after centuries of civilization has come only to the place where 

 he can appreciate these processes but cannot duplicate them? 



Innumerable attempts have been made both by philosophers and 

 biologists to find a natural explanation of this fundamental phenom- 

 enon of life. One need only enumerate the " perfecting principle " 

 of Aristotle, the " active teleological principle " of Kant, Lamarck- 

 ism, Darwinism, several kinds of selection, and finally the " ente- 

 lechy " of Driesch to indicate over what a field these explanations 

 have ranged. 



If for the present we disregard those views which really attempt 



PROC. AMER. PHIL. SOC. XLVIII. I9I D*, PRINTED JULY /, I909. 



