36 THE ORIGIN OF SPECIES 



same tree under uniform conditions, has been known sud- 

 denly to assume a new character; and as buds on distinct 

 trees, growing under different conditions, have sometimes 

 yielded nearly the same variety — for instance, buds on 

 peach-trees producing nectarines, and buds on commoQ 

 roses producing moss-roses — we clearly see that the nature 

 of the conditions is of subordinate importance in com- 

 parison with the nature of the organism in determining 

 each particular form of variation; — perhaps of not more 

 Importance than the nature of the spark, by which a 

 mass of combustible matter is ignited, has in determining 

 the nature of the flames. 



Effects of Habit and of the Use or Disuse of Parts; 

 Correlated Variation; Inheritance 



Changed habits produce an inherited effect, as in the 

 period of the flowering of plants when transported from 

 one climate to another. With animals the increased use 

 or disuse of parts has had a more marked influence; 

 thus I find in the domestic duck that the bones of the 

 wing weigh less and the bones of the leg more, in pro- 

 portion to the whole skeleton, than do the same bones in 

 the wild duck; and this change may be safely attributed 

 to the domestic duck flying much less, and walking 

 more, than its wild parents. The great and inherited 

 development of the udders in cows and goats in countries 

 where they are habitually milked, in comparison with 

 these organs in other countries, is probably another in- 

 stance of the effects of use. Not one of our domestic 

 animals can be named which has not in some country 

 drooping ears; and the view which has been suggested 

 that the drooping is due to disuse of the muscles of the 



