No one ought to feel surprise at much remaining as yet unexplained in regard to the origin of species and varieties, if he makes due allowance for our profound ignorance in regard to the mutual relations of all the beings which live around us. Who can explain why one species ranges widely and is very numerous, and why another allied species has a narrow range and is rare? Yet these relations are of the highest importance, for they determine the present welfare, and, as I believe, the future success and modification of every inhabitant of this world. Still less do we know of the mutual relations of the innumerable inhabitants of the world during the many past geological epochs in its history. Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which most naturalists entertain, and which I formerly entertained--namely, that each species has been independently created--is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification. * * * * * {7} CHAPTER 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.