x VARIATION UNDER DOMESTICATION 31 



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only a few being kept by poor people, and little attention paid to 

 their breeding; for recently in certain parts of Spain and of the 

 United States this animal has been surprisingly modified and im- 

 proved by careful selection ; in peacocks, from not being very easily 

 reared and a large stock not kept; in geese, from being valuable 

 only for two purposes, food and feathers, and more especially from 

 no pleasure having been felt in the display of distinct breeds ; but 

 the goose, under the conditions to which it is exposed when domes- 

 ticated, seems to have a singularly inflexible organization, though 

 it has varied to a slight extent, as I have elsewhere described. 



Some authors have maintained that the amount of variation in 

 our domestic productions is soon reached, and can never afterward 

 be 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 

 the body to be carried, and the power of contraction in the mus- 

 cular 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 Saint Hilaire has 

 proved this in regard to size, and so it is with color, 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 comparably stronger, than any two natural species be- 

 longing to the same genus. So with plants, the seeds of the dif- 

 ferent 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 organization, 

 and indirectly by affecting the reproductive system. It is not prob- 

 able that variability is an inherent and necessary contingent, under 

 all circumstances. The greater or less force of inheritance and re- 





