216 THE PHILOSOPHY OF BIOLOGY 



the elements were originally arranged. That would be 

 radical finalism. 



Science must reject this notion as it rejects that of 

 special creation, since it introduces indeterminism 

 into the evolutionary process. It must regard the 

 organism and its environment as a physico-chemical 

 system studied from without. It must avoid all 

 attempts to acquire an intuitive knowledge of the 

 actions of the organism, for the latter, and the things 

 which environ it, are only bodies moving in nature. 

 In the systems studied by it time must be the inde- 

 pendent variable, and there must be a strict function- 

 ality between the parts of the organism and the parts 

 of the reacting environment, so that any change in 

 the one must necessarily be dependent on a change 

 in the other. Such a system and series of interactions 

 is that which is described in a mechanistic hypothesis 

 of transformism. 



All this is indeed suggested to ordinary and aided 

 methods of observation. The plant or animal acts 

 upon, and is acted on by, the environment, though it 

 is usually the modification of the organism to which 

 we attend. A man's face becomes reddened by wind 

 and sun and rain ; manual labour roughens his hands 

 and develops callosities ; in the summer he sweats 

 and loses heat ; in the winter the blood-vessels of his 

 skin contract and heat is economised. In the winter 

 months the fur of many animals becomes more luxu- 

 riant and may change in colour. Fishes which inhabit 

 lightly coloured sand are lightly pigmented, but their 

 skins become dark when they move on to darkly 

 coloured sea-bottoms ; prawns which are brown when 

 they live on brown weed, become green when they 

 are placed on green weed. Birds migrate into warmer 

 countries, and vice versa, when the seasons change. 



