Shadows of Forgotten Ancestors

Other commentators raised more substantial objections: No example of a beneficial mutation or hereditary change is known, it was said; Darwin must invoke enormous intervals of time before the epoch of the dinosaurs, and yet no sign of life could be found in the earlier geological record; transitional forms between one species and the other were said to be wholly lacking in the geological record. In fact Darwin stressed the almost total ignorance in his time of the nature of hereditary transmission and mutation, and he himself pointed to the sparseness of the geological record as a problem for the theory (although he also said he would produce the transitional fossils when his opponents showed him all the intermediate forms between wild dogs and greyhounds, say, or bulldogs). Since then, not only have the laws of inheritance by genes and chromosomes (which are made entirely of nucleic acids) been carefully worked out, but their detailed molecular structure is known; we even understand how a mutation can be caused by the substitution of a single atom for another. The geological record has been extended not only to before the time of the dinosaurs, but we now have spotty glimpses of life through the preceding 3.5 billion years. Despite his exhaustive studies of artificial selection, Darwin did not know of a single case history of natural selection in the wild; today we know of hundreds.⁸ The fossil evidence remains sparse, though: A few more transitional forms are now known—Archeopteryx, for example, a halfway house between reptile and bird—but still not nearly enough to show even the majority of the important evolutionary pathways. But the most powerful evidence for evolution comes, as we will see, from a science whose very existence was unknown in Darwin’s time—molecular biology.

A critique in The North American Review for April 1860 attempts to refute Darwin by a kind of unselfconscious sophism: The very long periods of geological time required for evolution are declared “virtually infinite.” Darwin himself used similarly loose mathematical language. Then the review goes on to assert that “the difference between such a conception and that of the strictly infinite, if any, is not appreciable.” Infinity, however, belongs not to science but to metaphysics, so the reviewer concludes that the theory of evolution is not scientific but metaphysical—“resting altogether upon the idea of ‘the infinite,’ which the human mind can neither put aside nor comprehend.”⁹ This last point would seem to apply, especially, to the reviewer. In fact, any two numbers, no matter how large or small, are equally distant from infinity, and 4.5 billion years is a respectably finite period of time. Infinity does not enter the evolutionary perspective. The speciousness of this argument (and other critiques) gives us a sense of how anxious people were to reject Darwin’s ideas. (His later suggestion that all living things including humans were still evolving, and that in the far future our descendants would not be human, was dismissed even by sympathetic reviewers as going too far.)

In The London Quarterly Review of July 1860, in an article called “Darwin’s Origin of Species,” Darwin is anonymously taken to task by his adversary Samuel Wilberforce, the Anglican Bishop of Oxford—among many other things, for “wantonness of conjecture” and “extravagant liberty of speculation.” His “mode of dealing with nature” is condemned asutterly dishonourable to all natural science, as reducing it from its present lofty level as one of the noblest trainers of man’s intellect and instructors of his mind, to being a mere idle play of the fancy, without the basis of fact or the discipline of observation.

He is accused of circumventing “the obstinacy of fact” by waving a magic wand and saying, “ ‘Throw in a few hundreds of millions of years more or less, and why should not all these changes be possible …?’ ”