CHAPTER I 



VARIATION UNDER DOMESTICATION 



Causes of Variability — Effects of Habit — Correlation of Growth- 

 Inheritance— Character of Domestic Varieties— Difficulty of dis- 

 tinguishing between Varieties and Species — Origin of Domestic 

 Varieties from one or more Species — Domestic Pigeons, their 

 Differences and Origin — Principle of Selection anciently followed, 

 its Effects — Methodical and Unconscious Selection — Unknown 

 Origin of our Domestic Productions — Circumstances favourable 

 to Man's power of Selection. 



When we look to 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. When 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, I think we are driven 

 to conclude that this great variability is simply due to 

 our domestic productions having been raised under con- 

 ditions of life not so uniform as, and somewhat different 

 from, those to which the parent- species have been 

 exposed under nature. There is also, I think, some 

 probability in the view propounded by Andrew Knight, 

 that this variability may be partly connected with 

 excess of food. It seems pretty clear that organic 

 beings must be exposed during several generations to 

 the new conditions of life to cause any appreciable 

 amount of variation ; and that when the organisation 

 has once begun to vary, it generallv continues to varv 



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