CONTENTS. 



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 ^| 

 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 throughout 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 i\> organism the most important of all relations • • 



j. 



