But however much Lyell may have "smoothed the road," Huxley, and most of the biologists of those thirty years, declined to go in thereat. It remained for an anonymous amateur, whom they thereupon with one accord fell to abusing, to point out the practicability of that highway. In the "Vestiges" and the "Explanations" Chambers urged the presumption from geological uniformitarianism with an effective use of concrete examples.[2]
If there is anything more than another impressed on our minds by the course of geological history, it is that the same laws and conditions of nature now apparent to us have existed throughout the whole time. Admitting that we do not now see any such fact as the production of new species, we at least know that, while such facts were occurring upon earth, there were associated phenomena of a perfectly ordinary character. For example, when the earth received its first fishes, sandstone and limestone were forming in the manner exemplified a few years ago in the ingenious experiments of Sir James Hall. . . . It was about the time of the first mammals that the forest of the Dirt Bed was sinking in natural ruin amidst the sea sludges, as the forests of the Plantagenets have been doing for several centuries upon the coast of England. In short, all the common operations of the physical world were going on in their usual simplicity, obeying the laws which we now see governing them; while the supposed extraordinary causes were in requisition for the development of the animal and vegetable kingdoms. There surely hence arises a strong presumption against any such causes.
It is a curious circumstance, however, that the argument from uniformitarianism cut both ways. As Wallace says:
One of the greatest, or perhaps we may say the greatest, of all the difficulties in the way of accepting the theory of natural selection as a complete explanation of the origin of species, has been the remarkable difference between varieties and species with respect to fertility when crossed."[3]
This difference, as Darwin said in the "Origin," seemed, on the face of it, "to make a broad and clear distinction between varieties and species." And the apparent existence of such a radical distinction between the varieties produced under domestication and true physiological species was an objection, not only against natural selection, but also against evolution itself; for it meant that we do not see now, nor within the limits of human observation, organisms actually getting
