Origin of Species Variorum

Comparison with 1861

Circumstances favourable to Natural Selection .—

This is an extremely intricate subject. A large amount of variability will evidently be favourable for the work of natural selection, but mere individual differences probably suffice. A large number of individuals, by giving a better chance for the appearance within any given period of profitable variations, will compensate for a lesser amount of variability in each individual, and is, I believe, an extremely important element of success. Though Nature grants vast periods of time for the work of natural selection, she does not grant an indefinite period; for as all organic beings are striving ... to seize on each place in the economy of nature, if any one species does not become modified and improved in a corresponding degree with its competitors, it will soon be exterminated. Unless favourable variations be inherited by some at least of the offspring, nothing can be effected by natural selection. Non-inheritance of any new character is, in fact, the same thing as reversion to the character of the grandparents or more remote ancestors; and no doubt the tendency to reversion may often have checked or prevented the action of natural selection; but its importance has been greatly exaggerated by some writers. If the tendency to reversion has not prevented man from creating innumerable hereditary races in the animal and vegetable kingdoms, why should it have stopped the process of natural selection?

In man's methodical selection, a breeder selects for some definite object, and free intercrossing will wholly stop his work. But when many men, without intending to alter the breed, have a nearly common standard of perfection, and all try to get and breed from the best animals, much improvement and modification surely but slowly follow from this unconscious process of selection, notwithstanding a large amount of crossing with inferior animals. Thus it will be in nature; for within a confined area, with some place in its polity not so perfectly occupied as might be, natural selection will always tend to preserve all the individuals varying in the right direction, though in different degrees, so as better to fill up the unoccupied place. But if the area be large, its several districts will almost certainly present different conditions of life; and then if natural selection be modifying and improving a species in the several districts, there will be intercrossing with the other individuals of the same species on the confines of each. ↑ And in

Circumstances favourable to Natural Selection. —

This is an extremely intricate subject. A large amount of inheritable and diversified variability is favourable, but I believe mere individual differences suffice for the work. A large number of individuals, by giving a better chance for the appearance within any given period of profitable variations, will compensate for a lesser amount of variability in each individual, and is, I believe, an extremely important element of success. Though nature grants vast periods of time for the work of natural selection, she does not grant an indefinite period; for as all organic beings are striving, it may be said, to seize on each place in the economy of nature, if any one species does not become modified and improved in a corresponding degree with its competitors, it will soon be exterminated. ↑