Chap. XX. SELECTION. 221 



the whole structure is admirably co-ordinated for certain pur- 

 poses, it has been supposed that all the parts must have been 

 simultaneously modified ; and it has been argued that, on the 

 principle of natural selection, this is scarcely possible. But in 

 thus arguing, it has been tacitly assumed that the variations must 

 have been abrupt and great. No doubt, if the neck of a ruminant 

 were suddenly to become greatly elongated, the fore limbs and 

 back would have to be simultaneously strengthened and modified ; 

 but it cannot be denied that an animal might have its neck, or 

 head, or tongue, or fore-limbs elongated a very little without 

 any corresponding modification in other parts of the body ; and 

 animals thus slightly modified would, during a dearth, have a 

 slight advantage, and be enabled to browse on higher twigs, and 

 thus survive. A few mouthfuls more or less every day would 

 make all the difference between life and death. By the repeti- 

 tion of the same process, and by the occasional intercrossing 

 of the survivors, there would be some progress, slow and fluc- 

 tuating though it would be, towards the admirably co-ordinated 

 structure of the giraffe. If the short-faced tumbler-pigeon, with 

 its small conical beak, globular head, rounded body, short wings, 

 and small feet — characters which appear all in harmony — had 

 been a natural species, its whole structure would have been 

 viewed as well fitted for its life ; but in this case we know that 

 inexperienced breeders are urged to attend to point after point,, 

 and not to attempt improving the whole structure at the same 

 time. Look at the greyhound, that perfect image of grace, 

 symmetry, and vigour ; no natural species can. boast of a more 

 admirably co-ordinated structure, with its tapering head, slim 

 body, deep chest, tucked-up abdomen, rat-like tail, and long 

 muscular limbs, all adapted for extreme fleetness, and for 

 running down weak prey. Now, from what we see of the 

 variability of animals, and from what we know of the method 

 which different men follow in improving their stock — some chiefly 

 attending to one point, others to another point, others again 

 correcting defects by crosses, and so forth— we may feel assured 

 that if we could see the long line of ancestors of a first-rate 

 greyhound, up to its wild wolf-like progenitor, we should behold 

 an infinite number of the finest gradations, sometimes in one 

 character and sometimes in another, but all leading towards our 



