CHAPTER I 



Variation Under Domestication 



Causes of Variability — Effects of Habit and the Use or Disuse of Parts — 

 Correlated Variation — Inheritance — Character of Domestic Varieties — 

 Difficulty of distinguishing between Varieties and Species — Origin of Do- 

 mestic Varieties from one or more Species — Domestic Pigeons, their 

 Differences and Origin — Principles of Selection, anciently followed, their 

 Effects — Methodical and Unconscious Selection — Unknown Origin of 

 our Domestic Productions — Circumstances favorable to Man's Power 

 of Selection. 



CAUSES OF VARIABILITY 



When we compare the individuals of the same variety or sub- 

 variety of our older cultivated plants and animals, one of the 

 first points which strikes us is, that they generally differ more 

 from each other than do the individuals of any one species or 

 variety in a state of nature. And if we reflect on the vast diversity 

 of the plants and animals which have been cultivated, and which 

 have varied during all ages under the most different climates and 

 treatment, we are driven to conclude that this great variability is 1/ 

 due to our domestic productions having been raised under condi- 

 tions of life not so uniform as, and somewhat different from, those 

 to which the parent species had been exposed under nature. There 

 is, also, some probability in the view propounded by Andrew 

 Knight, that this variability may be partly connected with excess 

 of food. It seems clear that organic beings must be exposed dur- / 

 ing several generations to new conditions to cause any great 

 amount of variation; and that, when the organization has once 

 begun to vary, it generally continues varying for many genera- 

 tions. No case is on record of a variable organism ceasing to vary 

 under cultivation. Our oldest cultivated plants, such as wheat, still 

 yield new varieties; our oldest domesticated animals are still 

 capable of rapid improvement or modification. 



As far as I am able to judge, after long attending to the sub- 

 ject, the conditions of life appear to act in two ways — directly 

 on the whole organization or on certain parts alone, and indirectly 

 ^by affecting the reproductive system. With respect to the direct 



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