70 



MY LIFE 



[Chap. 



charm of the study of nature. People continually ask, " If 

 scented leaves are such a protection, why do not all plants 

 have them ? If so many can do without them they cannot 

 be of any use." And the same objection is made to all the 

 other wonderful modes of protection by concealing colours or 

 patterns, by resembling uneatable or dangerous species, by the 

 production of spines or various kinds of armour. " Why are 

 not all protected ? " they say. " You admit that the majority 

 are without these kinds of protection, yet they all continue 

 to exist. The whole idea is therefore a delusion." And they 

 think they have thus destroyed a large part of Darwin's theory. 

 But all this shows that they are either ignorant of, or forget, 

 the main facts on which that theory is founded — the enormous 

 rate of possible increase of all organisms, the intensity there- 

 fore of the struggle to exist, since only the few best adapted 

 of these enormous numbers can survive to produce offspring ; 

 and also the undoubted fact that species vary enormously in 

 population, some being common over large areas, some com- 

 paratively scarce, others confined to very limited areas, others 

 again only existing in such small numbers and in such 

 restricted areas that they are very rarely found. Now, if 

 some great change of climate comes on slowly, such a mixed 

 population of species will be affected in different ways and 

 will require different modifications to become adapted to it. 

 Some will become extinct, some will be adapted in one way, 

 some in quite a different way, depending partly on the kind 

 and amounts of variation that occurs in each species. Some 

 will therefore become more numerous in individuals, others 

 less ; and when the complete change of climate has been 

 effected, we should find a new set of species, some differing 

 very little, others very greatly from the former inhabitants 

 of the district, but all fairly well adapted to live under the 

 new conditions. Taking the one case of the protected leaves, 

 it would be only those which were in some danger of exter- 

 mination by insect and other enemies that would develop 

 the various forms of protection by oil-glands, or hairs, or 

 spines, or by attracting stinging ants ; while many which 

 existed in great numbers and over wide areas, and which 



