Origin of Species… • 15. Recapitulation and conclusion (14)

≣  •  D a r w i n  (1 8 5 9,  1 8 7 2⁶)  •  15.  R e c a p i t u l a t i o n  a n d  c o n c l u s i o n  •  √it

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Now let us turn to the other side of the argument. Under domestication we see much variability, caused, or at least excited, by changed conditions of life; but often in so obscure a manner, that we are tempted to consider the variations as spontaneous. Variability is governed by many complex laws, — by correlated growth, compensation, the increased use and disuse of parts, and the definite action of the surrounding conditions. There is much difficulty in ascertaining how largely our domestic productions have been modified; but we may safely infer that the amount has been large, and that modifications can be inherited for long periods. As long as the conditions of life remain the same, we have reason to believe that a modification, which has already been inherited for many generations, may continue to be inherited for an almost infinite number of generations. On the other hand, we have evidence that variability when it has once come into play, does not cease under domestication for a very long period; nor do we know that it ever ceases, for new varieties are still occasionally produced by our oldest domesticated productions.

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[]  C h.  D a r w i n,  ‹T h e  O r i g i n  o f  S p e c i e s›,  J o h n  M u r r a y,  1 8 7 2⁶.
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