396 OUTLINES OF EVOLUTIONARY BIOLOGY 



As we saw in a previous chapter, the forms, colours and scents 

 of many flowers are probably the result of unconscious selection 

 by insects, extending over countless generations. It may be said 

 that the advantage gained in this case is mutual ; the insect gets 

 the honey and the flower gets fertilized. This of course is true, 

 but exactly the same is true of human selection. The sheep gets 

 the pasture and man gets the wool. 



It seems impossible to explain on any other hypothesis than 

 that of the natural selection and gradual accumulation of chance, 

 favourable variations, those marvellous adaptations of animals 

 which lead to protective resemblance and mimicry, for although 

 we may admit that an organ which is actively employed may be 

 modified by the efforts of an animal to maintain itself by the 

 use of that organ, we can hardly extend the same principle to 

 such passive features as colour and ornamentation, or the out- 

 growth of leaf -like dermal appendages and so forth. It may be 

 questioned if, even with the aid of natural selection, we can fully 

 account for all the wonderful phenomena of mimicry, for why, if 

 it be an advantage to some species to adopt a common warning 

 colour and band themselves together in synaposematic groups, 

 should it be desirable for others to do just the reverse and split 

 up into a number of differently coloured forms, each of which 

 mimics some particular model ? We can only say that we do 

 not know all the factors of the environment, and that until we do 

 our inability to solve the problem cannot be justly considered as 

 an argument against the efficacy of natural selection. 



It is, of course, extremely difficult, if not impossible, to obtain 

 direct evidence of the action of natural selection in modifying 

 species in a state of nature. Human life is all too brief to 

 admit of our making very satisfactory observations concerning 

 processes which extend perhaps over millions of years. Man 

 has, however, in a comparatively short space of time, so changed 

 the conditions of life for many of the lower animals as to lead, 

 albeit unintentionally, to the more or less complete extermina- 

 tion of many species, and by studying these cases we may hope 

 to arrive at sound conclusions as to what takes place in a state of 

 nature. After all, mankind is a part of nature and we have no 

 just reason for excluding his influence in our consideration of 

 the factors which have brought about the present condition of 

 the organic world. 



It is well known that many of the birds of various remote 



