ii2 PIONEERS OF EVOLUTION PART 



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, decided changes, in all 

 organisms subject to modifying influences. . . . 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, domesticated animals, and in the several 

 races of men, such alterations have taken place. 

 They can show that the degrees of difference so pro- 

 duced are often, as in dogs, greater than those on 

 which distinctions of species are in other cases 

 founded. 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 strengthening of 

 passions habitually gratified, and the weakening of 

 those habitually curbed the development of every 

 faculty, bodily, moral, or intellectual, according to 

 the use made of it are all explicable on this same 

 principle. And thus they can show that throughout 

 all organic nature there is at work a modifying in- 

 fluence of the kind they assign as the cause of these 

 specific differences ; an influence which, though slow 

 in its action, does, in time, if the circumstances 

 demand it, produce marked changes an influence 

 which, to all appearance, would produce in the 

 millions of years, and under the great varieties of 

 condition which geological records imply, any amount 

 of change. 1 



This quotation shows, as perhaps no other 



