xlviii THE DARWIN CENTENARY. [Februarys, 



III. 



Darwin's theory of evolution includes much more than the doc- 

 trine of descent; it attempts to explain by natural causes the won- 

 derful and exquisite adaptations of organisms to their conditions 

 of life. The deepest and most mysterious problems of biology do 

 not center in the structure of organisms, nor in their functions, nor 

 even in their oigin, but in their fitness. Everywhere the universe 

 is a cosmos and not a chaos ; " Order is heaven's first law ; " but this 

 order is especially evident in the organic world. The subject of 

 organic adaptations is undoubtedly a dangerous one for the scientist, 

 full of pitfalls for the unwary and with many alluring calls to meta- 

 physical speculation, but it is a subject which lies in the background 

 of every biological problem. " Life is," as Professor Brooks taught, 

 " response to the order of nature," and it is the element of useful, 

 apparently purposive, response, which more than anything else 

 distinguishes the living from the lifeless, and separates the methods 

 of biology from those of chemistry and physics. Indeed Herbert 

 Spencer defined life as " continuous adjustment of internal relations 

 to external relations"; lack of such adjustment invariably leading 

 to death. 



One cannot speak of any organ or tissue of an animal or plant 

 without illustrating such adjustment. Consider the fitness of the 

 skeleton for support, of the muscles for contraction, of the alimen- 

 tary system for digestion and absorption, of the heart with its valves 

 for pumping and the blood vessels for circulating blood. Consider 

 the truly remarkable contrivances for insuring cross-fertilization in 

 animals and plants and for the protection and nourishment of the 

 young. Consider the fitness of the nervous system for receiving 

 and transmitting stimuli ; the fitness of the eye for seeing, of the 

 ear for hearing, of the tongue for tasting. Think of the fitness of 

 every organ for its particular use, and then consider the peculiar 

 fitness with which these organs are coordinated into an harmonious 

 whole. Viewed in this light, " What a piece of work is man," or 

 any other organism ! 



Such adaptations to general conditions of existence are so com- 

 mon that to most persons they do not seem remarkable, while some 

 peculiar adaptation, such as the leaf insect, or the Venus fly-trap, 



