Chap. I. VARIATION UNDER DOMESTICATION. 



CHAPTEK I. 



Variation under Domestication. 



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

 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 — 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 much 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 greater 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 ex- 

 posed 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 generally continues to vary for many generations. 



