io8 PROBLEMS OF EVOLUTION 



in wild nature may have been equally rapid. The following 

 argument is one which has weight with me. All the main 

 groups have been long established and their chief characteristics 

 date from pre-historic ages. But there was a time when in the 

 vertebrates the characteristic features were recent attainments, 

 and consequently, if the view of breeders is correct, were more 

 likely to vary ; there was a time when in the bird-reptile or 

 reptile-bird feathers were a novelty and the great possibilities 

 that lay in them were only vaguely suggested. This opens the 



A possible question whether there is a limit to evolution along any particular 

 evolution ^ ne wnetner > for instance, a swift's wing has been so perfected 



on partic- that no further advance is possible ; so that, if there is to be a 

 es more perfect living flying-machine, nature must start low down 

 in the scale on another plan and from there work upward. On 

 such a subject we can merely speculate, but for myself, I cannot 

 help believing that in some cases the greatest perfection attain- 

 able on the lines followed has been already attained. At any 

 rate we know enough of the methods and of the course of 

 evolution to feel certain that the range of variation for the 

 highest species is limited. It is absurd to demand, as has been 

 demanded, that in order to prove the Darwinian theory, a new 

 kind of animal should be produced by scientific breeding, that 

 the breeder of horses should turn out not merely a new variety 

 of horse but a breed different enough to rank as an entirely new 

 species. If such a thing is possible, it is for nature to prove it, 

 not for man. It would require hundreds of thousands of years, 

 an experiment such as nature alone can make. And it may be 

 that even she in order to produce any striking novelty would 

 have to begin with some more simple form and work laboriously 

 upward. 



But for nature as for man, I think it is now impossible to 

 begin low down in the scale of animal life and from that develop 

 some higher form. Even the lower types of life are highly 

 specialised. The Ornithorhyncus, the lowest of mammals, is 

 near to perfection on his own level. The Hydra is little but 

 a stomach and tentacles to catch food for the stomach. True, 

 but the tentacles are marvels of adaptation. The fact is that 



