THE WONDER OF LIFE 579 



adaptation of the vertebrate structure to a terrestrial life '. 

 It had not circumscribed its possibiUties, and perhaps 

 there is something in Professor Shaler's suggestion, that 

 the possession of an internal instead of an external skeleton 

 was a factor in giving free play to the evolutionary potency 

 which lay concealed in these unpromising amphibians of 

 the Carboniferous forest-swamps. 



The Fitness of the Environment. — ^A favourite idea 

 of olden times was expressed in the phrase the harmony of 

 nature, the theory being that the physical conditions, for 

 instance, were suitable for life. The universe was regarded 

 as distinctly friendly. This idea has been rehabihtated 

 in Professor Lawrence J. Henderson's recent essay on 

 The Fitness of the Environment (1913), to which we wish 

 briefly to refer. When a crust forms on a heavenly body, 

 hke our earth, the normal envelope is an atmosphere 

 containing water and carbonic acid gas, which are necessarily 

 and automatically formed in vast amounts by the cosmic 

 process. They are very fit things in themselves, and fitted 

 to play an important role in inorganic evolution, but the 

 point is that they also exhibit extraordinarily great and 

 detailed fitness in relation to the upbiiilding and susten- 

 ance of living creatures. Their exceptional properties 

 have contributed to the success of Mfe. There are no other 

 compounds which share more than a small part of the 

 qualities of fitness which water and carbonic acid possess ; 

 and no other elements which share those of carbon, hydro- 

 gen and oxygen. Living means trafficking with the environ- 

 ment ; to do this effectively organisms must be complex and 

 yet coherent, plastic and yet durable ; and they were able 

 to gain these qualities because of the fundamental pro- 

 perties of the primary constituents of the inanimate environ- 



