228 CLASSICS OF MODERN SCIENCE 

 occur. Others have objected that the term selection implies conscious 

 choice in the animals which become modified ; and it has even been 

 urged that, as plants have no volition, natural selection is not ap- 

 plicable to them ! In the literal sense of the word, no doubt, natural 

 selection is a false term; but who ever objected to chemists speaking 

 of the elective affinities of the various elements? — and yet an acid 

 cannot strictly be said to elect the base with which it in preference 

 combines. It has been said that I speak of natural selection as an 

 active power or Deity ; but who objects to an author speaking of 

 the attraction of gravity as ruling the movements of the planets? 

 Everyone knows what is meant and is implied by such meta- 

 phorical expressions ; and they are almost necessary for brevity. 

 So again it is difficult to avoid personifying the word Nature; but 

 I mean by Nature, only the aggregate action and product of many 

 natural laws, and by laws the sequence of events as ascertained by 

 us. With a little familiarity such superficial objections will be for- 

 gotten. 



We shall best understand the probable course of natural selection 

 by taking the case of a country undergoing some slight physical 

 change, for instance, of climate. The proportional numbers of its 

 inhabitants will almost immediately undergo a change, and some 

 species will probably become extinct. We may conclude, from what 

 we have seen of the intimate and complex manner in which the in- 

 habitants of each country are bound together, that any change in 

 the numerical proportions of the inhabitants, independently of the 

 change of climate itself, would seriously affect the others. If the 

 country were open on its borders, new forms would certainly immi- 

 grate, and this would likewise seriously disturb the relations of some 

 of the former inhabitants. Let it be remembered how powerful the 

 influence of a single introduced tree or mammal has been shown to 

 be. But in the case of an island, or of a country partly surrounded 

 by barriers, into which new and better adapted forms could not freely 

 enter, we should then have places in the economy of nature which 

 would assuredly be better filled up, if some of the original inhabitants 

 were in some manner modified ; for, had the area been open to im- 

 migration, these same places would have been seized on by intruders. 

 In such cases, slight modifications, which in any way favoured the 

 individuals of any species, by better adapting them to their altered 



