[In reference to the belief that species were independently created] To admit this view is, as it seems to me, to reject the real for the unreal, or at least an unknown, cause. It makes the works of God a mere mockery and deception; I would almost soon believe that the old and ignorant cosmologists, that fossil shells had never lived, but but had been created in stone so as to mock the shells living of the sea-shore.
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Any part or organ developed to an extraordinary size or in an extraordinary manner, in comparison with the same part or organ in the allied species, must have gone through an extraordinary amount of modification since the genus arose; and thus we can understand why it should often still be variable in a much higher degree than other parts; for variation is a long-continued and slow process, and natural selection will in such cases not as yet have had time to overcome the tendency to further variability and to reversion to a less modified state.
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On the theory of natural selection we can clearly understand the full meaning of that old canon in natural history, 'Natura non facit saltum.' This canon, if we look only to the present inhabitants of the world, is not strictly correct, but if we include all those of past times, it must by my theory be strictly true.
"Natura non facit saltum" meaning Nature does not make jumps. Here Darwin is saying that, though things may jarring and random when looking at the development of species, evolution comes into focus when looking at a species history.
He who believes that some ancient form was transformed suddenly through an internal force or tendency into, for instance, one furnished with wings, will be almost compelled to assume, in opposition to all analogy, that many individuals varied simultaneously. It cannot be denied that such abrupt and great changes of structure are wildly different from those that most species have apparently undergone. He will further be compelled to believe that many structures beautifully adapted to all of the other parts of the same creature and the surrounding conditions, have been suddenly produced; and of such complex and wonderful co-adaptations, he will not be able to assign a shadow of an explanation. He will be forced to admit that these great and sudden transformations have left no trace of their action on the embryo. To admit all this is, as it seems to me, to enter into the realms of miracle, and to leave those of Science.
In Mivart's criticisms of natural selection, he sees an "internal force" at work in the evolution of each species. Here Darwin forcefully counters this while at the same time giving a tremendous amount of fuel to his critics who believe in a scriptural interpretation of evolution which he implicitly dismisses here as well.
