Chap.l Circumstantes fawiirable to Selection. 3X 



especially from ao pleasure **™Z beenfelt inthedisplay of distinct; 

 Ws • but the goose, under the conditions to which it is exposed 

 when domesticated, seems to have a singularly inflexible organisa- 

 tion, though it has varied to a slight extent, as I have elsewhere 



described. _ . . 



Some authors have maintained that the amount of variation m. 

 our domestic productions is soon reached, and can never afterwards- 

 he exceeded. It would be somewhat rash to assert that the limit 

 has been attained in any one case ; for almost all our animals and. 

 plants have been greatly improved in many ways within a recent 

 period ; and this implies variation. It would be equally rash to 

 assert that characters now increased to their utmost limit, could 

 not, after remaining fixed for many centuries, again vary under 

 new conditions of life. No doubt, as Mr. Wallace has remarked 

 with much truth, a limit will be at last reached. For instance,, 

 there must be a limit to the fleetness of any terrestrial animal, as 

 this will be determined by the friction to be overcome, the weight 

 of body to be carried, and the power of contraction in the muscular 

 fibres. But what concerns us is that the domestic varieties of the- 

 same species differ from each other in almost every character, which 

 man has attended to and selected, more than do the distinct species- 

 of the same genera. Isidore Geoffroy St. Hilaire has proved this in 

 regard to size, and so it is with colour and probably with the length 

 of hair. With respect to fleetness, which depends on many bodily 

 characters, Eclipse was far fleeter, and a dray-horse is incomparably 

 stronger than any two natural species belonging to the same 

 genus. So with plants, the seeds of the different varieties of the- 

 bean or maize probably differ more in size, than do the seeds of 

 the distinct species in any one genus in the same two families. 

 The same remark holds good in regard to the fruit of the several, 

 varieties of the plum, and still more strongly with the melon, as 

 well as in many other analogous cases. 



To sum up on the origin of our domestic races of animals and 

 plants. Changed conditions of life are of the highest importance in, 

 causing variability, both by acting directly on the organisation, and 

 indirectly by affecting the reproductive system. It is not probable 

 that variability is an inherent and necessary contingent, under all 

 circumstances. The greater or less force of inheritance and rever- 

 sion determine whether variations shall endure. Variability is 

 governed by many unknown laws, of which correlated growth is 

 probably the most important. Something, but how much we do- 

 not know, may be attributed to the definite action of the conditions 

 of life. Some, perhaps a great, effect may be attributed to the 



