Shadows of Forgotten Ancestors

by Carl Sagan

  … [H]ardly any one is so careless as to breed from his worst animals …

  If there exist savages so barbarous as never to think of the inherited character of the offspring of their domestic animals, yet any one animal particularly useful to them, for any special purpose, would be carefully preserved during famines and other accidents, to which savages are so liable, and such choice animals would thus generally leave more offspring than the inferior ones; so that in this case there would be a kind of unconscious selection going on …

  Man … can never act by selection, excepting on variations which are first given to him in some slight degree by nature …

  This preservation [in Nature] of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest Variations neither useful nor injurious would not be affected by natural selection …

  When we see leaf-eating insects green, and bark-feeders mottled-grey; the alpine ptarmigan white in winter, the red-grouse the colour of heather, we must believe that these tints are of service to these birds and insects in preserving them from danger …

  If it profit a plant to have its seeds more and more widely disseminated by the wind, I can see no greater difficulty in this being effected through natural selection, than in the cotton-planter increasing and improving by selection the down in the pods on his cotton-trees …

  There is no reason why the principles which have acted so efficiently under domestication should not have acted under nature. In the survival of favoured individuals and races, during the constantly-recurrent Struggle for Existence, we see a powerful and ever-acting form of Selection. The struggle for existence inevitably follows from the high geometrical ratio of increase which is common to all organic beings. This high rate of increase is proved by calculation,—by the rapid increase of many animals and plants during a succession of peculiar seasons, and when naturalised in new countries. More individuals are born than can possibly survive. A grain in the balance may determine which individuals shall live and which shall die,—which variety or species shall increase in number, and which shall decrease, or finally become extinct … The slightest advantage in certain individuals, at any age or during any season, over those with which they come into competition, or better adaptation in however slight a degree to the surrounding physical conditions, will, in the long run, turn the balance.4

  In his 1858 paper in the Linnaean Society Proceedings, he asks us to imagine a being who could continue selecting, with unfailing attention, for a single desired characteristic over “millions of generations.” Natural selection implies—in effect, although not literally—that such a being exists. “We have almost unlimited time” for evolution, he wrote.

  Darwin then went on to propose that, over such immense periods of time, continuing natural selection may generate such a divergence of an organism from its parental stock as to constitute a new species. Giraffes develop long necks because those whose necks are—by some spontaneous genetic variation—a little longer are able to browse on the topmost foliage, flourish when others are ill-fed, and leave more offspring than their shorter-necked fellows. He pictured a vast family tree, symbolic of the varied forms of life, slowly growing, branching, and anastomosing, organisms evolving to produce all the “exquisite adaptations” of the natural world.

  There is “grandeur,” he thought, in the fact that “from so simple a beginning, endless forms most beautiful and most wonderful have been, and are being evolved.”

  Analogy would lead me one step farther, namely, to the belief that all animals and plants are descended from some one prototype. But analogy may be a deceitful guide. Nevertheless all living things have much in common, in their chemical composition, their cellular structure, their laws of growth, and their liability to injurious influences.… [O]n the principle of natural selection with divergence of character, it does not seem incredible that, from such low and intermediate form, both animals and plants may have been developed; and, if we admit this, we must likewise admit that all the organic beings which have ever lived on this earth may be descended from some one primordial form.

  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.

  ——

  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 mummifie
r’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.)

  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 as

  utterly 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 …?’ ”

  The terrible implication is drawn that Darwin’s unexpressed supposition was that “man” might be only “an improved ape.” (Wilberforce on this point was not far from the mark; this is close to what Darwin thought.) That natural selection might apply to humans is denounced as “absolutely incompatible” with “the Word of God.” Moreover, “man’s derived supremacy over the earth; man’s power of articulate speech; man’s gift of reason; man’s free-will and responsibility; man’s fall and man’s redemption; the Incarnation of the Eternal Son; the indwelling of the Eternal Spirit, all are equally and utterly irreconcilable with the degrading notion of the brute origin of him who was created in the image of God, and redeemed by the Eternal Son.” The idea of evolution tends “inevitably to banish from the mind most of the peculiar attributes of the Almighty.” Darwin’s insights are compared to “the frenzied inspiration of the inhaler of mephitic gas.” His views are contrasted by Bishop Wilberforce with those of “a far greater philosopher,” Professor Owen, whom he quotes, a little tangentially, as advising teenagers:

  Oh! you who possess it in all the supple vigour of lusty youth, think well what it is that He has committed to your keeping. Waste not its energies; cull them not by sloth; spoil them not by pleasures! The supreme work of creation has been accomplished that you might possess a body—the sole erect—of all animal bodies the most free—and for what? for the service of the soul . . Defile it not.10

  The North British Review of May 1860, no less hostile, begins its critique: “If notoriety be any proof of successful authorship, Mr. Darwin has had his reward.” Darwin is compared with writers who “seem ever distrustful of views of nature which, even remotely, tend to set them or their readers in direct relation with a personal God.” As in many of the negative reviews, this one acknowledges Darwin’s reputation as an accomplished naturalist and praises his felicity of style. He is, though, a “charlatan” and guilty of “unbelief in the governing Creator.” The book’s “seeming depth is only darkness.” He is accused of setting a throne “somewhere, above Olympus, and the goddess of the author’s devotion is seated on it.” This goddess is Natural Selection. “The ‘chance’ of heathenism has developed into a higher form … Mr. Darwin’s work,” The North British Review concludes, “is in direct antagonism to all the findings of a natural theology, formed on legitimate inductions in the study of the works of God; and it does open violence to everything which the Creator Himself has told us in the Scriptures of truth.” The publication of The Origin of Species is said to have been a “mistake.” “Its author would have done well to science, and to his own fame, had he, being determined to write it, put it away among his papers, marked, ‘A Contribution to Scientific Speculation in 1720’ ” —that being the reviewer’s estimate of how retrogressive and passé Darwin’s argument was.11

  The process of natural selection, extracting order out of chaos as if by magic, was counterintuitive and disturbing to many, and Darwin was repeatedly accused of something not far short of idolatry. He answered the charge in these words:

  It has been said that I speak of natural selection as an active power or Deity; but who objects to an author speaking of the attraction of gravity as ruling the movements of the planets? Every one knows what is meant and is implied by such metaphorical expressions; and they are almost necessary for brevity. So again it is difficult to avoid personifying the word Nature; but I mean by Nature, only the aggregate action and product of many natural laws, and by laws the sequence of events as ascertained by us. With a little familiarity such superficial objections will be forgotten …

  As man can produce, and certainly has produced, a great result by his methodical and unconscious means of selection, what may not natural selection effect? Man can act only
on external and visible characters: Nature, if I may be allowed to personify the natural preservation or survival of the fittest, cares nothing for appearances, except in so far as they are useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life. Man selects only for his own good: Nature only for that of the being which she tends …

  It may metaphorically be said that natural selection is daily and hourly scrutinising, throughout the world, the slightest variations; rejecting those that are bad, preserving and adding up all that are good; silently and insensibly working … We see nothing of these slow changes in progress, until the hand of time has marked the lapse of ages, and then so imperfect is our view into long-past geological ages, that we see only that the forms of life are now different from what they formerly were.