Written in Stone: Evolution, the Fossil Record, and Our Place in Nature

by Brian Switek

  The idea that the birth and death of organisms were regulated by natural laws was becoming more acceptable. This view was formally articulated by Charles Babbage in his unofficial Ninth Bridgewater Treatise. It was not enough to look at the pattern of nature and say, “This fossil reptile speaks of God,” Babbage argued, but the process by which the Creator’s thoughts were translated also required elucidation. For Babbage it seemed that relatively simple laws of mathematics and physics could build up to become components of even grander laws that regulated the machinations of the universe. If this was true then it was not unreasonable that the Creator regulated life by similar means.

  FIGURE 15 - The skeleton of an Ichthyosaurus.

  Babbage took the geological record, both of the rocks themselves and the remains of ancient life contained within them, as a proof of this trend. Strange forms flourished in ages past only to be wiped out and replaced by superior creatures better suited to the changing world. All of this, Babbage proposed, was governed by elegant, simple laws that the Creator imposed upon the matter of the universe, knowing full well from the beginning how history would unfold.

  Yet this new vision of change according to natural laws posed new problems. Whatever applied to the rest of nature applied to our species, too, so it could not be argued that our species was the product of a miracle when such intervention had been foresworn from the rest of nature. It was impossible not to recognize our resemblance to apes and monkeys, but to think that we had actually descended from such animals was still enough to make many naturalists shudder. Such fears over the bestialization of humanity made a tract anonymously published in 1844 an instanst sensation. Entitled Vestiges of the Natural History of Creation , it was both beloved and despised.

  Published anonymously by the Scottish publisher Robert Chambers, Vestiges complemented Babbage’s view of natural change. The fossil record, especially, provided unequivocal evidence that Providence had set laws to regulate evolution, but contrary to Darwin’s private notion that evolution was not progressive Chambers believed that life strove ever upward through time, with each stage forming the foundation for the next. Life followed the great hierarchy: fish, amphibians, reptiles, birds, and mammals all appeared according to the traditional order. This was closely tied to changes on the globe, with each group fitted to different environments by biological destiny.

  As far as vertebrates were concerned, Chambers believed embryos had a fixed destiny, and different groups diverged earlier in the process than others depending on the conditions of the environment at the time. If the development along this path was stopped early, a fish was produced; if it was allowed to progress a mammal was formed. The process could be sped up or slowed down, but external factors did not so much change embryos as bring about predestined changes:Thus, the production of new forms, as shewn in the pages of the geological record, has never been anything more than a new stage of progress in gestation, an event as simply natural, and attended as little by any circumstances of a wonderful or startling kind, as the silent advance of an ordinary mother from one week to another of her pregnancy. Yet, be it remembered, the whole phenomena are, in another point of view, wonders of the highest kind, for in each of them we have to trace the effect of an Almighty Will which had arranged the whole in such harmony with external physical circumstances, that both were developed upon our planet is but a sample of what has taken place, through the same cause, in all other countless theatres of being which are suspended in space.

  Written in a plain manner accessible to almost any adult reader, Vestiges was an immediate hit and began running through new editions quickly. Chambers’s conclusions were in doubt, but whether or not he was correct was overshadowed by the controversial idea that life was not locked into a static order. The vanguard of traditional religion was quick to respond. A reply published the following year by S. R. Bosanquet opened with a tsk, tsk at the public’s credulity, likening Chambers’s freewheeling discussion to a “wanton and deformed adulteress,” that seduced minds that should be focused on God. Others, while not so severe in their rhetoric, made similar charges, and for a time there was a small industry of books denouncing Vestiges. The scientific theorizing in the book was bad enough, but among the most vocal critics were those who were offended by Chambers’s theology.

  Charles Darwin, who had written out a private sketch of his evolutionary theory two years earlier, was both charmed and frustrated by Vestiges, especially since some readers attributed it to his hand. No one was quite sure what he was cooking up, but by the time Vestiges was published a number of naturalists knew that he was actively considering how life might evolve. He even cultivated a close group of expert friends—among them Charles Lyell, the botanist Joseph Hooker, and Richard Owen’s young rival Thomas Henry Huxley—to help him formulate his ideas on the subject.

  Hooker broached the subject of the Vestiges with Darwin soon after its publication, writing that he was “delighted” by its spirit even if it was scientifically unsound. Darwin replied that he was not nearly as amused, for “[Chambers’s] geology strikes me as bad, & his zoology far worse.” This made him feel “much flattered & unflattered” at the suggestion that he had written it. Even so, Vestiges provided a test whereby Darwin could see how people might react to such ideas. The withering criticisms Chambers’s book received confirmed that Darwin needed to make a solid, convincing case based upon hard evidence that would be respected by his naturalist peers. He already had the mechanism that would produce the expected pattern of life seen throughout history, but he would have to gather even more data to make the operation of this “secondary law” consistent with life both past and present.

  To this end Darwin corresponded with authorities, carried out breeding experiments with fancy pigeons, studied barnacles, and built up the solid base of observation required to support his theory. This would all culminate in what he referred to as the “Big Book,” tentatively called Natural Selection, which would present the full theory to his colleagues.

  A work of such importance could not be rushed, but not everyone would wait up for Darwin to get on with publishing. While Darwin settled down to a quiet life in the country with his wife and family, the tales of his adventures in South America aboard the Beagle inspired other younger naturalists. Among these were Henry Walter Bates and Alfred Russel Wallace, two Englishmen who resolved to travel to South America to solve the question of the origin of species.

  In 1848, Bates and Wallace sailed for Brazil, and once they arrived they pushed into the jungle along the Amazon River. They worked together at first, but after growing tired of one another’s company they split up and continued the endeavor separately. Their respective journeys would be very different. Whereas Bates remained in the Amazon until 1859, by 1852 Wallace had collected enough specimens to sell in England, including living birds, coatis, monkeys, and other vertebrates that Wallace had to pull along with him and feed every day. After an arduous journey back out of the jungle, Wallace made it to a port near the coast and was able to secure passage on a boat home.

  A few days later, Wallace watched as a fire that had started onboard consumed the ship, leaving him and his fellow passengers stranded at sea. Save for a few notes, everything was gone. It was ten days before another ship rescued him and the other survivors in the lifeboat.

  Once home, Wallace lacked the financial security that had been bequeathed to Darwin and, like other naturalists such as T. H. Huxley, he worked feverishly to pursue his passion. With the exception of a few esteemed professorships doled out by colleges or prestigious societies, there were no official jobs for naturalists. They had to make their own opportunities, either by entering the medical profession or becoming collectors and selling the exotic specimens they found. Wallace was a master at the latter craft, and after a stint of eighteen months (during which he introduced himself to the growing scientific elite of England through several books and papers), Wallace was off again, this time for the South Pacific, to collect more specimens. />
  Wallace arrived on the Malay Archipelago in 1854, and he would remain there for eight years. This time, though, he sent his findings back home at intervals. Among the most significant was an 1855 paper entitled, “On the Law Which Has Regulated the Introduction of Species.” While it did not explain precisely how organisms evolved, Wallace did notice that new species closely resembled those already in existence, meaning that evolutionary steps were built upon what had come before.

  This sounded very familiar to some naturalists back in England, particularly Charles Lyell and Edward Blyth, both of whom knew of Darwin’s thoughts on the same subject. Blyth, in particular, shot off a hastily written and rambling note about it to Darwin right after the paper’s publication, pointing out the similarities between what Wallace had been proposing and what Darwin had been working on for two decades. Darwin did not take the hint. He thought that Wallace was proposing another variation of progressive creation that was of no threat to his own nascent theory. Yet Wallace’s article was enough to get Lyell thinking more seriously about species change, and in 1856 Darwin finally explained his hypothesis to his mentor. Lyell did not agree but knew that if Darwin did not publish soon his primacy would be in danger. Rather than try to hide his theoretical ambitions, however, Darwin let Wallace in on what he had kept from so many other naturalists. On May 1, 1857, Darwin wrote to Wallace (who was still in Indonesia).

  FIGURE 16 -Alfred Russel Wallace, photographed in Singapore in 1862.

  I can plainly see that we have thought much alike & to a certain extent have come to similar conclusions. In regard to the Paper in Annals, I agree to the truth of almost every word of your paper; & I daresay that you will agree with me that it is very rare to find oneself agreeing pretty closely with any theoretical paper; for it is lamentable how each man draws his own different conclusions from the very same fact.—

  This summer will make the 20th year (!) since I opened my first-notebook, on the question how & in what way do species & varieties differ from each other.—I am now preparing my work for publication, but I find the subject so very large, that though I have written many chapters, I do not suppose I shall go to press for two years.—

  Wallace replied that he was glad that someone was at least interested in his paper (many of those who read it wished he would just get back to collecting and stop theorizing), and that he, too, intended to more fully explicate his hypothesis. Since Wallace planned to remain in the field for three or four more years, Darwin believed that he would have ample time to write up his unique perspective on evolution.

  Darwin was not prepared for the shock that hit on June 18, 1858. Enclosed in a letter was an essay Wallace had written that was strikingly similar to what Darwin had been working on for years. Wallace recognized that evolution could be affected by natural selection, and even used some of the same phrases that Darwin employed. Darwin panicked. He immediately wrote to Lyell that his “words have come true with a vengeance that I shd. be forestalled,” and was in such a frantic state that he rushed off two additional letters before Lyell replied to the first.

  Even though Wallace did not present specific instructions to publish the paper, Darwin could think of a no more honorable course. If he did not pass the paper along he would certainly be accused of suppressing Wallace’s work to the advantage of his own. Even worse, Darwin’s baby son, Charles, was sick with scarlet fever and passed away on June 28. It seemed like Darwin’s life was unraveling even as he approached the exposition of the idea he had labored over for so long.

  FIGURE 17 - Charles Darwin in 1854, just a few years prior to the publication of On the Origin of Species.

  Darwin’s confidants Hooker and Lyell devised a compromise. In a public joint announcement before the Linnean Society, Wallace’s essay would be presented with one of Darwin’s sketches of his ideas and a few letters; it was all that Darwin could put together on such short notice, even though he had never intended for them to be read publicly.

  The ideas presented in the documents were very similar, yet not exactly identical. Darwin, for his part, couched his mechanism in explicitly Malthusian terms:Now, can it be doubted, from the struggle each individual has to obtain subsistence, that any minute variation in structure, habits, or instincts, adapting that individual better to the new conditions, would tell upon its vigour and health? In the struggle it would have a better chance of surviving; and those of its offspring which inherited the variation, be it ever so slight, would also have a better chance. Yearly more are bred than can survive; the smallest grain in the balance, in the long run, must tell on which death shall fall, and which shall survive. Let this work of selection on the one hand, and death on the other, go on for a thousand generations, who will pretend to affirm that it would produce no effect, when we remember what, in a few years, Bakewell effected in cattle, and Western in sheep, by this identical principle of selection?

  The analogy to the modification of domesticated animals was important. Everyone knew that a judicious farmer, by determining which individuals of his stock could breed, could create entirely distinct varieties of livestock in a matter of years. If humans could do it, why not nature? Yet this was just one part of what Darwin was proposing. If there really is a struggle for existence we should expect for nature to produce a diverse variety of species such that numerous organisms could all live in the same place.

  The varying offspring of each species will try (only few will succeed) to seize on as many and as diverse places in the economy of nature as possible. Each new variety or species, when formed, will generally take the place of, and thus exterminate its less well-fitted parent. This I believe to be the origin of the classification and affinities of organic beings at all times; for organic beings always seem to branch and sub-branch like the limbs of a tree from a common trunk, the flourishing and diverging twigs destroying the less vigorous—the dead and lost branches rudely representing extinct genera and families.

  Darwin did not imagine evolution as striving to a preconceived end as Chambers and others did, but it could be said that each new species was superior (or at least better adapted to the new conditions) than its ancestor and so would outcompete its progenitor. Thus the origin and death of species were inextricably tied together as life branched out to fill all available spaces.

  Wallace, however, started on a different tack. He began by saying that domesticated animals were not a good example of how evolution might work, for it was well known that domesticated animals released into the wild would eventually return to the “wild type.” It was only natural selection in the wild that could effect permanent change, but from there Wallace’s remarks are eerily similar to Darwin’s. Just like Darwin, Wallace saw variations providing advantages to some individuals and not others, and under times of extreme environmental stress the newly formed species would be superior to the parent stock. There were plenty of dead branches in the tree of life. Evolution by natural selection made sense of both the process and pattern of evolution, leaving Wallace to conclude:This progression, by minute steps, in various directions, but always checked and balanced by the necessary conditions, subject to which alone existence can be preserved, may, it is believed, be followed out so as to agree with all the phenomena presented by organized beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit.

  The Linnean Society was not impressed. Natural selection was a well-known phenomenon and was thought to have no great effect on nature. At best it was a preserving force that caused species to remain stable, and at worst it was a destructive force that was the antithesis of creative power. The naturalist Patrick Matthew, for one, had anticipated what Darwin and Wallace called natural selection in 1831 when he published a passage on the mechanism as a preserving force in the appendix of the obscure volume On Naval Timber and Arboriculture. The fact that he buried it in such an out-of-the-way place gives some indication of his estimation of its importance. The head of the Lin
nean Society, Thomas Bell, had a similar estimation of evolution by natural selection. According to him, 1858 passed without a single idea of special importance coming up in the society.

  FIGURE 18 - The only illustration in On the Origin of Species—a diagram of evolution’s branching pattern.

  Both Darwin and Wallace were disappointed by the way other scientists shrugged off the idea that both had been working on for so long, but for Darwin, at least, this was something of a blessing. If the idea was not given special attention, neither did it generate the firestorm of controversy he had for so long feared. Now he had to quickly publish an abstract of his full views before someone else scooped him. This abstract, a shadow of what Natural Selection was meant to be, was called On the Origin of Species by Means of Natural Selection.

  Darwin opened his book by recapitulating the development of his ideas. “When on board H.M.S. ‘Beagle,’ as a naturalist,” Darwin explained, “I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent.” The “succession of types” Darwin saw firsthand had set him on the trail of “that mystery of mysteries,” evolution, but at that time the fossil record presented more problems than solutions.

  According to Darwin’s theory, evolution was gradual. This did not mean that evolution proceeded at a constant pace, but that it happened in a graded, stepwise fashion. There was a continuity of forms, and if these forms could all be traced they would coalesce into a nested hierarchy of successively older common ancestors. In 1859 the fossil record as a whole was consistent with what evolution predicted, with the appearance of different vertebrate types occurring in a sensible fashion (fish before amphibians, amphibians before reptiles, etc.), but a direct fossil confirmation of what Darwin was proposing was, as yet, unidentified.