86 PROBLEMS OF EVOLUTION 



for the evolution of species, and Lord Kelvin doles out the 

 millions of years available with a parsimonious hand. If it be 

 objected that the circumstances are artificial, that breeders upset 

 the ways of nature, the answer is easy ; the breeder is a new 

 environment, hence a new kind of variation finds favour, but the 

 question of the maintenance of a large variation through pre- 

 potency remains unaffected. 



It has been maintained that all production of new species has 

 been due to large variations suddenly appearing. But this can 

 hardly be the case. Among domesticated animals and plants 

 such variations occur, there is reason to believe, more often than 

 in wild nature, but breeders while making use of them when 

 they have occurred have steadily accumulated the small changes 

 through long series of generations. The results are patent. 

 And what has been done by man we cannot doubt that Nature 

 also has done. In some ways she has had the advantage, in 

 other ways she has been at a disadvantage. She has begun at 

 the bottom of the scale and so has had plastic material to work 

 upon : she has had millions of years to elaborate each form. 

 Man has worked upon species that were already highly special- 

 ised and whose range of variation was, therefore, limited, and he 

 has had comparatively but a few years for his experiments. On 

 the other hand he has usually sought to produce only one or 

 two characters, the rest he has left as he found them. In the 

 horse he has aimed only at speed or strength ; teeth and hoofs he 

 has left as they were. Nature has striven after a combination of 

 characters, a more difficult feat in breeding. But we cannot feel 

 sure that several have been attained in the same period. It is 

 highly probable that Nature has often, so to speak, bred for 

 the improvement of some new character and merely for the 

 maintenance of others that were well established. 



Take as an imaginary instance, a race of vultures that re- 

 quired greater keenness of sight; all enhancement of wing 

 power may have been shelved till this was attained. Supposing 

 that many members of the race through defective sight could 

 not find carrion or arrived only after other scavengers had 

 disposed of it, selection would undoubtedly be on these lines. 



