The third reason why most naturalists around 1835 were slow to admit the fact of evolution was neither a religious nor a moral objection. It was a purely intellectual one. By now it has been almost completely forgotten, no doubt because we labor under the handicap of hindsight. But it was a well-founded objection at the time.
If someone says a certain thing has happened, and it is of a kind which has never been actually witnessed by anyone, it is reasonable to doubt what he says, if no one can think of any explanation of what he says has happened. It is on this principle that you would doubt my word, if I were to tell you (for example) that electrical storms follow me wherever I go. Now this was exactly how matters stood with evolutionism around i835.
No naturalist claimed, of course, to have ever seen a new species evolve out of an older one. Yet the evolutionists said that, whenever new species do come into existence, that is the way they do it. But what could be the explanation of one species’ giving rise to another? What causes or forces are there, already known to exist in nature, which would make one kind of grass or fish or mammal evolve into a different kind? Where is the vera causa, as they used to say, or (as we would say), where is the mechanism, which could drive this alleged process of evolution?
It should go without saying that this was not only a purely intellectual objection, but a good objection, to evolutionism. The main evidence for evolution was the fossil record, which reveals in countless instances the arrival of a new species which is closely related to an earlier one. In 1835 most naturalists regarded these new species as brought about by exercises of God’s creative power; whereas the evolutionists regarded them as developments or evolutions of the older species in question. No one had ever witnessed any of these exercises of Divine power, of course, but then exactly the same was true of evolutions of one species into another; no one had ever witnessed an instance of that, either. And then, to ascribe new species to God’s creative power is at least an explanation of a kind, though doubtless not of a very satisfactory kind. But the evolutionists, for their part, had no explanation of any kind to suggest for their alleged process of evolution.
Darwin, being a rational man, naturally felt the force of this objection, just as strongly as did his fellow naturalists who were not evolutionists. For several years around 1836, it weighed heavily on his mind. These were the very same years when the reality of evolution was being constantly impressed upon him, by the multitude of facts which would be explained if it were true. But the trouble, and a very big trouble, was that he could not think of anything which would explain evolution. That was the rub, and it seemed to Darwin that he was staring at a blank wall.
Given the intellectual circumstances of the time, it is not surprising that, just a few years later, another young naturalist found himself brought to a standstill by exactly the same blank wall. This was Alfred Wallace. Though neither of them knew it, his early intellectual career had been exactly the same as Darwin’s. On the one hand, he had become convinced of the reality of evolution; but on the other, he was altogether at a loss as to how to explain it.
Why should there be any evolution at all? Why should not the species which exist at a given time exist forever, without any new ones ever being added, or old ones subtracted? But it is not the subtractions which are the problem: presumably climatic or topographical changes, and general wear and tear, will sometimes bring about the extinction of a species. The problem is the new additions. Why should any new species ever come into existence at all? That is the mystery of the origin of species, which both Darwin and Wallace long brooded over in vain.
To ordinary observation, of course, it does not look as though new species ever do come into existence. But it is clear from the fossil record that the reality is very different. In countless thousands of instances, new species of organisms have appeared on earth. Organic nature is in fact, whatever else it is, a gigantic species-generating engine. Now, why in the world would it be that? What force can it possibly be, which drives this gigantic engine? It might reasonably be thought to be some Divine force, in view of the irresistibility of its operations, and the length of time that those operations have been going on all over the earth. But if it is not a Divine force, what force is it?
David Stove, Darwinian Fairytales: Selfish Genes, Errors of Heredity, and Other Fables of Evolution (New York, NY: Encounter Books, 1995), 24-26. (Emphasis Added)