In considering the Origin of Species, it is quite conceivable that a naturalist, reflecting on the similarities of organic beings, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified so as to acquire that perfection of structure and co-adaptation which most justly excites our admiration.
It is, therefore, of the highest importance to gain a clear insight into the mechanism of change. At the start of my observations it seemed to me probable that a careful study of domesticated animals and of cultivated plants would offer the best chance of solving this obscure problem. Nor have I been disappointed; in this and in all other perplexing cases I have invariably found that our knowledge, imperfect though it be, of variation under domestication, afforded the best and safest clue.
Although much remains obscure, and will long remain obscure, I am certain, after the most deliberate study and dispassionate judgement 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 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. urthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification.
