172 



HABIT AND INTELLIGENCE. 



[chap. 



Habit ift 

 change- 

 able, 



which is easily taught to point because his ancestors have 

 been taught before him, is similar to that of a man who 

 once learned to practise an art or to speak a language, 

 and, though he has forgotten it, can learn it again much 

 more easily than he could if he had never known it. The 

 fact of the dog's ancestors having learned to point gives 

 the same facility to the dog himself in learning it, which 

 the fact of the man having once learned an art gives him 

 in learning it again. -^ 



Another most important law of habit must be formally 

 stated, though it is implied in what has been said about 

 the acquisition of new habits. It is, that all habits are 

 in some degree changeable. New habits are constantly 

 produced by change of circumstances, and by education, 

 which indeed is only a special and artificial set of circum- 

 stances : and this could not be the case if habits were not 

 in some degree changeable, 

 and spon- But besides the cliangecLbility of habit as the result of 

 ^^^rf br''^ changing circumstances, there is a certain amount of spon- 

 taneous variability, which does not depend — at least not 

 directly — on change of circumstances. I^o child is exactly 

 like either of its parents, and no two children of the same 

 parents are exactly alike. These differences might be 

 attributed to differences of circumstances acting on the 

 offspring through the parents ; but such an explanation is 

 shown to be at least insufficient, by the fact that the same 

 differences are found to exist between twins, though, in 

 general, in a somewhat less degree than between other 

 children of the same parents ; and it is obvious that twins 

 have been subjected to precisely the same influences. The 

 same is very generally true of those domesticated races of 

 animals which produce several young at a birth. 



It is a most important, and a much debated question, 

 whether there is any limit to spontaneous variation. 

 Variation in a single generation is beyond doubt confined 

 within very narrow limits : no such variations appear to 

 be possible (among the higher animals and vegetables at 

 least) as would be implied in " gathering grapes of thorns 



' See l$aiu on the Emotions and the Will, Appendix C. 



