152 CONCLUSION [ch. 



that sucli a change should appear suddenly, complete 

 from the start. And if so there is no difficulty in sup- 

 posing that it might be of some advantage to its 

 possessor through the resemblance to an unpalatable 

 form. Even were the advantage but a slight one it 

 is clear from previous discussion (p. 96) that the new 

 variety would more or less rapidly replace the form 

 from which it had sprung. With the continued 

 operation of natural selection the new form would 

 entirely supplant the original one, but it is not im- 

 possible that in some cases the selecting agent may be 

 removed before this result has been achieved. In this 

 event the proportions of the new and the old form 

 would faU into a condition of equilibrium as in P. 

 polytes in Ceylon, until some other selective agent 

 arose to disturb the balance. On this view natural 

 selection is a real factor in connection with mimicry, 

 but its function is to conserve and render preponderant 

 an already existing Ukeness, not to build up that like- 

 ness through the accumulation of small variations, as 

 is so generally assumed. Recent researches in heredity 

 and variation all point to this restriction of the scope 

 of natural selection. Hitherto an argument in favour 

 of the older view has been that derived from the study 

 of adaptation — of an apparent purpose, which, at first 

 sight, appears to be behind the manner in which 

 animals fit into their surroundings. For many the 

 explanation of this apparent purpose has been found 

 in the process of natural selection operating gradually 

 upon small variations, accumulating some and rejecting 



