And how did such a primordial form arise? In 1871, Darwin wistfully imagined, in a letter to his friend Joseph Hooker, “But if (and oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a proteine compound was chemically formed, ready to undergo still more complex changes …”5
If such a thing were possible, why isn’t it happening today? Darwin immediately foresaw one reason: “At the present day, such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.” In addition, we now know that the absence of the oxygen molecule in the atmosphere of the primitive Earth made the formation and survival of organic molecules then much more likely. (And vastly more organic molecules were falling from the sky than do so today in our tidied-up and regularized Solar System.) That warm little pond—or something like it—laboratory experiments show, could have quickly produced the amino acids. Amino acids, energized a little, readily join up to make something like “a proteine compound.” In related experiments, simple nucleic acids are made. Darwin’s guess, as far as it went, is today pretty well confirmed. The building blocks of life were abundant on the early Earth, although we certainly cannot yet say we fully understand the origin of life. But we humans, starting with Darwin, have only just begun to look into the matter.
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The publication of The Origin of Species met, as might have been expected, with a passionate response, both pro and con, including a stormy meeting of the British Association for the Advancement of Science shortly after publication. The larger debate can perhaps best be glimpsed by disinterring the literary reviews of the day. These magazines, generally published monthly, covered the widest range of topics—fiction and nonfiction, prose and poetry, politics, philosophy, religion, and science. Reviews of twenty printed pages were not uncommon. Almost all articles were unsigned, although many were written by the leading figures in their fields. Comparable publications in the English language seem sparse today, although The Times of London’s Literary Supplement and The New York Review of Books perhaps come closest.
The Westminster Review of January 1860 recognized that Darwin’s book might be of historic significance:If the principle of Modification by Natural Selection should be admitted to anything like the extent to which Mr. Darwin would carry it … a grand and almost untrodden field of inquiry will be opened … Our classifications will come to be, as far as they can be so made, genealogies; and will then truly give what may be called the plan of creation.6
The Edinburgh Review of April 1860 (in an unsigned critique by the anatomist Richard Owen) took a less charitable view:The considerations involved in the attempt to disclose the origin of the worm are inadequate to the requirements of the higher problem of the origin of man … To him, indeed, who may deem himself devoid of soul and as the brute that perisheth, any speculation, pointing, with the smallest feasibility, to an intelligible notion of the way of coming in of a lower organised species, may be sufficient, and he need concern himself no further about his own relations to a Creator … Mr. Darwin offers us … intellectual husks … endorsed by his firm belief in their nutritive sufficiency.7
The reviewer praises scientists “who trouble the intellectual world little with their beliefs, but enrich it greatly with their proofs,” and contrasts them to Darwin, who is said to have no more than “a discursive and superficial knowledge of nature.”
Professor Owen is much impressed by the work of Cuvier on the mummified ibises, cats, and crocodiles “preserved in the tombs of Egypt,” which prove “that no change in their specific characters has taken place during the thousands of years … which had elapsed … since the individuals of those species were the subjects of the mummifier’s skill.” Cuvier’s data, it is said, were of “far higher value” than the “speculations” of Darwin. But the mummified animals of ancient Egypt walked the Earth only a split second ago on the geological time scale—not nearly long enough ago to show major evolutionary change, which characteristically requires millions of years. Owen’s review ripples with florid scorn: “Prosaic minds,” it says, “are apt to bore one by asking for our proofs, and one feels almost provoked, when seduced to the brink of such a draught of forbidden knowledge as the [evolutionists] offer, to have the Circean cup dashed away” by more knowledgeable experts of a different opinion.
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.)