CONTENTS. 



paos 



introduction 1 



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 unconscious selection — Unknown 

 origin of our domestic productions — Circumstances favor- 

 able to man's power of selection 6 



CHAPTER II. 



VARIATION UNDER NATURE. 



Variability — Individual differences — Doubtful species — Wide 

 ranging, much diffused, and common species, vary most — 

 Species of the larger genera in each country vary more fre- 

 quently than the species of the smaller genera — Many of the 

 species of the larger genera resemble varieties in being very 

 closely, but unequally, related to each other, and in having 37 

 restricted ranges 



CHAPTER III. 



STRUGGLE FOR EXISTENCE. 



Its bearing on natural selection — The term used in a wide sense 

 — Geometrical ratio of increase — Rapid increase of natural- 

 ized animals and plants — Nature of the checks to increase--— 

 Competition universal — Effects of climate — Protection from 

 the number of individuals — Complex relations of all animals 

 and plants througbout nature — Struggle for life most severe 

 between individuals and varieties of the same species: often 

 severe between species of the same genus — The Relation of 

 organism to organism the most important of all relatione . • 



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