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wliicli arises almost spontaneously^ — ^if we are to assume 

 that there exists in every race the tendency to an un- 

 limited progressive improvement. There are certainly 

 no observations on record which would, in the smallest 

 degree, countenance such an hypothesis. Many animals 

 and plants, it is true, are capable of considerable modifi- 

 cations and changes, for the better, — very much more 

 than is the case with others. But what does this prove, 

 except that their capacity for advancement has a slightly 

 wider compass than that of their allies ? It touches not 

 the fact, that the boundaries of their respective ranges 

 are absolutely and critically defined. It is moreover a 

 siugular phsenomenon, and one ia which the strongest 

 proofs of design (or a primary adjustment of limits with 

 a view to the future) may be discerned, that the mem- 

 bers of the organic creation which display the greatest 

 adaptive powers, are those which were apparently des- 

 tined to become peculiarly attendant upon man. " The 

 best-authenticated examples," says Sir Charles Lyell, 

 "of the extent to which species can be made to vary 

 may be looked for in the history of domesticated animals 

 and cidtivated plants. It usually happens that those 

 species which have the greatest phabUity of organiza- 

 tion, those which are most capable of accommodating 

 themselves to a great variety of new circumstances, are 

 most serviceable to man. These only can be carried by 

 him into different climates, and can have their pro- 

 perties or instincts variously diversified by differences of 

 nourishment and habits. If the resources of a species 



