Change is Normal 305 



to maintain it against growing adversity, or against compe- 

 tition of its own kind; sometimes to promote it or maintain 

 it better under nearly constant circumstances. If the effect 

 of a change is beneficial, the creature will prosper more for 

 it, and those deficient in it will prosper less; and so two 

 groups may be formed, and separated, except as they merge 

 by the interbreeding which sexual reproduction provides. In 

 time many or all of the race or group will have produced, 

 or adopted by blood relationship, the improvement, and it 

 will become established by persistent use and need; and 

 those who have it not, will either lapse into separate place 

 as an inferior variety, or will become extinct if it is of vital 

 value. Another fact corelated is that disuse of an endow- 

 ment for a long continued time will, by withdrawing the 

 stimulus of activity from it, allow it to deteriorate and even 

 to disappear. Examples are abundant showing a kind of 

 progress in certain desired abilities, obtained by a morpho- 

 logical change which is regressive. The foundation of the 

 single-toed foot of the horse by exaggerated development of 

 one toe of each foot, into strength and hardness of material, 

 is at the sacrifice of the others, which, being unused, become 

 slowly atrophied, generation by generation, until some dis- 

 appear from external view altogether. Geological specimens 

 of horses of antecedent form are well known, and they 

 afford examples of the transitional form of foot, when 

 the toes were not so fully transformed, the change being in 

 course of evolution. Also familiar is the change in the 

 human foot under civilization. It is well known that 

 savages, and even some civilized people, use the foot bare, 

 and with much use of the toes for prehensile and grasping 



