88 CHARLES DARWIN 



sophical a biologist may be regarded as the high-water 

 mark of evolutionary thinking up to the date of the 

 appearance of Wallace and Darwin's theory : 



'Even could the supporters of the development 

 hypothesis merely show that the production of species 

 by the process of modification is conceivable, they 

 would be in a better position than their opponents. 

 But they can do much more than this ; they can show 

 that the process of modification has effected and is 

 effecting great changes in all organisms, subject to 



modifying influences they can show that any 



existing species animal or vegetable when placed 

 under conditions different from its previous ones, imme- 

 diately begins to undergo certain changes of structure 

 fitting it for the new conditions. They can show that 

 in successive generations these changes continue until 

 ultimately the new conditions become the natural ones. 

 They can show that in cultivated plants and domesti- 

 cated animals, and in the several races of men, these 

 changes have uniformly taken place. They can show 

 that the degrees of difference, so produced, are often, as 

 in dogs, greater than those on which distinctions of 

 species are in other cases founded. They can show 

 that it is a matter of dispute whether some of these 

 modified forms are varieties or modified species. They 

 can show too that the changes daily taking place in 

 ourselves ; the facility that attends long practice, and 

 the loss of aptitude that begins when practice ceases ; 

 the development of every faculty, bodily, moral or in- 

 tellectual, according to the use made of it, are all ex- 

 plicable on this same principle. And thus they can 

 show that throughout all organic nature there is at 



