108 THE EVOLUTION THEORY 



a small one. But if there arise within it a variation in the food- 

 instinct whereby a second and it may be a commoner plant becomes 

 available, then the normal number of the species will rise, and perhaps 

 the original number of individuals may be more than doubled. It is, 

 however, by no means necessary to assume that the species was 

 previously in process of decadence : on the contrary its normal number 

 may have remained quite constant. 



So, in the case of the mimetic butterflies, we do not need to 

 assume that they all previously required protection in the sense that 

 they would have become extinct had they not assumed a likeness to 

 an immune species. We may indeed conclude, on other grounds, that 

 it was the rarer species which increased their number of individuals 

 by the mimetic protection, and in doing so they certainly enhanced 

 at the same time their chance of survival as a species. In the 

 more abundant species mimetic resemblance to species whose unpalata- 

 bility rendered them immune could not have been evolved, as it 

 would have been disadvantageous, not only for the model, but for the 

 mimicking species itself, while in species less rich in individuals, such 

 resemblance would necessarily have a protective value, no matter 

 whether the species was in danger of extinction or not. The process 

 of selection must have started simply because the mimetic individuals 

 survived more frequently than the others, and the mimetic resem- 

 blance must have gone on increasing as long as the increase brought 

 with it a more effective protection. It is, therefore, a fallacious 

 objection to say that a species, whose existence was threatened, 

 would, considering the slowness of the process of selection, have 

 died out altogether before it could have acquired effective protection 

 by mimicking an immune species. The assumption is false — the 

 widespread, hazy idea that the process of natural selection can only 

 begin when the existence of the species is threatened. On the 

 contrary, every species utilizes every possibility of improvement ; and 

 every improvement for which variation supplies the necessary 

 material is possible. The augmentation of the profitable variations 

 follows as a necessity from the more frequent survival of the best- 

 adapted individuals, and this ' more frequent survival ' will be not 

 only a relative one, due to the fact that the better adapted indi- 

 viduals will be less decimated, it will also be absolute, because more 

 individuals of the species will survive than before. Of this Papilio 

 inxerope may serve as an example : in Madagascar in now flies about 

 only slightly varied from the original form, var. meriones. Here, 

 therefore, the species is maintained, without the aid of mimetic 

 protection. We do not know if the reason for this lies in the absence 



