VARIATION UNDER DOMESTICATION. 



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 Domestic Varieties from one or more Species 



— Domestic Pigeons, their Differences and Origin — Principles of 

 Selection, anciently followed, their Effects — Methodical and Un- 

 conscious Selection — Unknown Origin of our Domestic Produc- 

 tions — 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 con- 

 clude that this great variability is due to our domestic pro- 

 ductions having been raised under conditions 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 during several generations to new conditions to cause 

 any great amount of variation ; and that, when the organiza- 

 tion has once begun to vary, it generally continues varying 

 for many generations. No case is on record of a variable 

 organism ceasing to vary under cultivation. Our oldest cul- 

 tivated plants, such as wheat, still yield new varieties ; our 

 oldest domesticated animals are still capable of rapid improve- 

 ment or modification. 



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

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

 directly on the whole organization or on certain parts alone, 



