510 THE WONDER OF LIFE 



activities, where one might attribute some of the effective- 

 ness to practice, is equally true of activities which are only- 

 occasional, e.g. those connected with animal courtship 

 and parenthood. Almost every detail of specific structure 

 and specific behaviour may be interpreted as adaptive. 

 This term might simply mean that the structure or function 

 in question is fit, effective, well adjusted, making for the 

 preservation or well-being of the individual or of the species ; 

 but in biological usage it has also a theoretical imphcation 

 — that the detail in question, if it be part of the hereditary 

 constitution or some expression of it, is the resuU of a 

 process of evolution. It was not always as it is now, it has 

 a history behind it, it is a product of the factors of evolu- 

 tion, whatever these may be. 



There can be no doubt that no small part of the pleasure 

 we have in the contemplation of hving creatures is related 

 to their effective fitness. As Sir J. Burdon Sanderson once 

 said in a lecture, ' the dehght and interest with which the 

 forms, colours, and structure of animals and plants fiU us is 

 derived from the conscious or unconscious perception by 

 our minds of their adaptation — their fitness for the place 

 they are intended to occupy '. He even went so far as to 

 declare his behef that our artistic perception of beauty 

 in nature is in great measure derived from the same source. 



In working towards a clear idea of one of the fimdamental 

 facts of biology — ^the adaptiveness of structure and func- 

 tion — ^it may be useful to consider three other facts — 



(1) Effectiveness of response; (2) plasticity; and 

 (3) modifiability. 



(1) Effectiveness of response. — As we have already 

 seen, effectiveness of response is one of the distinctive pecu- 

 liarities of living creatures. Many inanimate things 



