ORIGIN OF SPECIES 



CHAPTER I 

 Variation under Domestication 



Causes of variability — Effects of habit and the use or disuse of parts- 

 Correlated variation — Inheritance — Character of domestic varie- 

 ties — Difificulty of distinguishing between varieties and species — 

 Origin of domestic varieties from one or more species — Domestic 

 pigeons, their differences and origin — Principles of selection, an- 

 ciently followed, their efifects — Methodical and unconscious 

 selection — Unknown origin of our domestic productions — Circum- 

 stances favourable 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 varia- 

 bility is due to our domestic productions 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 genera- 

 tions to new conditions to cause any great amount of varia- 

 tion; and that, when the organisation has once begun to 

 vary, it generally continues varying for many generations. 

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

 wnder cultivation. Our oldest cultivated plants, such as 



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