Charles Darwin’s theory of how life evolves through natural selection was first published more than 140 years ago. It’s a simple, elegant hypothesis with enormous power to explain the world we live in, yet paradoxically it remains misunderstood or ignored by many nonscientists. Indeed, as Steve Jones points out in Darwin’s Ghost, Charles Darwin’s magnum opus, The Origin of Species by Means of Natural Selection, is rarely read today. Nevertheless, the concept of Darwinian natural selection is still exerting an ever-expanding influence in a surprisingly broad range of academic disciplines.
In his opening pages Jones gives us a concise account of how natural selection works: “Errors of descent”—Jones’s shorthand for genetic variation caused by mutation—
are the stuff of evolution. Variation in the ability to copy them—natural selection—gives it a direction. Nature does not favor beauty, or strength, or ferocity; all it can do is to advance those best able to multiply themselves. Although its products include the most beautiful and most repulsive of beings there is no mystery to Darwin’s machine: it is no more than genetics plus time.
Jones calls natural selection “the factory for the almost impossible.” The concept is an important one, for the seemingly improbable idea that such complex organs as the eye result from evolution has long been a stumbling block to acceptance of Darwin’s theory for many. Jones writes that not only is the eye the result of evolution, but that
the eye happened…fifty times, and the problem of how to extract information from light has been solved in a dozen ways. The eye is as intricate as it needs to be, and no more. Its apparent perfection does not destroy but upholds the theory of evolution.
That is, the eye, in its various versions from fly to primate, improved the ability of very different creatures to multiply.
For George Bernard Shaw such explanations diminished the world. “When its [natural selection’s] whole significance dawns on you, your heart sinks into a heap of sand within you. There is a hideous fatalism about it, a ghastly and damnable reduction of beauty and intelligence, of strength and purpose, of honour and aspiration.” Perhaps such feelings are part of the reason why Darwin’s idea has met such resistance in the popular mind.
The desire to know how life began has been one of humanity’s enduring passions, and until the publication of Christopher Wills and Jeffrey Bada’s The Spark of Life, no explanation I know of has included natural selection as a factor. Indeed, as they make clear, until the nineteenth century investigations into life’s origin always mixed observation of the natural world with a touch of the divine. The Spark of Life commences with an engaging overview of these early researches. One of the first to approach the problem in a systematic manner was the seventeenth-century Florentine Francesco Redi, physician to the Medicis. Redi had become curious about where the maggots that consume corpses come from. Were they generated spontaneously from rotting flesh, or did they arrive from elsewhere? He left some meat exposed and other pieces under muslin. The screened meat did not become maggot-infested, indicating to Redi that the flies that swarmed over the uncovered meat had produced the maggots. Redi carried out this remarkably modern-sounding controlled experiment not in the spirit of science, but out of strict adherence to Creationist principles.
Bereshit—In the beginning—the great book rings out as it commences the story of the seven days of creation. Redi fervently believed the story, as do millions of Christians, Jews, and Muslims today. To them spontaneous generation of life after that seventh day is heretical.
Before humanity could inquire into the origins of life in a wholly secular way, a complete revolution in the way people thought about their place in the world had to occur. The critical moment in that revolution came in 1859 when Darwin published The Origin of Species. Yet even Darwin believed that “in the beginning” life was “breathed by the Creator into a few forms or into one” and that evolution via natural selection came later.
Before long, however, belief in the initiating role of a divine creator waned, and for nearly a century the majority of Darwinian thinkers inhabited a world where there was no one “in the beginning.” Life, they believed, arose in the distant past as a result of the interaction of organic chemicals in an ocean of “primordial soup.” Yet ideas about precisely how life might have arisen remained vague, largely because no experimental work was carried out. The reason for this is not discussed by Wills and Bada, but if Shelley’s Frankenstein speaks for the age, then perhaps some residual reverence for the divine prerogative in creation was responsible.
A major advance was made in 1953, when Stanley Lloyd Miller—a twenty-three-year-old second-year graduate student in the Department of Chemistry at the University of Chicago—decided to grasp the rudder of this directionless debate. He would attempt to be there, in the beginning, as the creator of life or its precursors, albeit in a flask.
What Miller did was relatively simple: he mixed methane, ammonia, hydrogen, and water vapor in a sealed glass flask, then sent electric sparks through the mixture. In doing so he created some of the basic building blocks of life—the amino acids that are found in proteins. His first experiment resulted in the creation of a small amount of glycine, the simplest amino acid. Later he was able to synthesize thirty-three different amino acids, including over half of the twenty found in proteins.
The reason Miller mixed the chemicals he did, then passed an electric charge through them, lay in his understanding of what the Earth might have been like when life arose. Now we know much more about that world of four billion years ago—enough to see the limitations of Miller’s work—and to cause us to marvel at the way life has changed planet Earth.
No rocks survive from that ancient time before life, but tiny zircon crystals found embedded in younger rocks in Canada and at a place called Mount Narryier in western Australia do. Mount Narryier is a forbidding place—a weathered brown knob of a hill standing over an endless sea of sand, where life is reduced to a few spiny shrubs and bizarre, rock-imitating lizards.
The Spark of Life takes us on an imaginary stroll along a beach that must have existed somewhere near Mount Narryier four billion years ago, and then the region was even more hostile. In order not to die upon inhaling your first breath, its authors warn us,
you must wear a space suit, for there is no oxygen in the atmosphere. And the suit will have to be Teflon coated, because nasty gases present in the thick air, such as hydrogen sulfide and the vapors of sulphuric and hydrochloric acids, would certainly kill you very quickly by eating through any protective suit made of ordinary chemicals.
Can you see your surroundings? Not very well—the atmosphere is so smoggy that little or no light can penetrate to the surface, even at high noon. But lightning flashes do give you brief, lurid glimpses of your immediate neighborhood. And you might be able to see the red glow of a nearby active volcano.
A vast ocean stretches away into the darkness and murk. During the brief lightning flashes, you can see that it is covered by lumps of oily material. The color of the water between the lumps is a muddy reddish brown, stained by large quantities of organic substances. Great waves crash on the shore, built up unimpeded to awesome size as they cross the vast stretches of ocean that girdle the planet. As they break, strong winds whip the sea up into a roiling mass of foam. Gusts of rain slash across the landscape.
Winds and tides together have produced the huge, sandy intertidal zone across which you are trudging.
This was a dynamic landscape indeed, a dynamism clearly absent from Miller’s tranquil experiment in a bottle. Wills and Bada see the tide as the most important life-creating force acting on this world, and the tide was then formidable. The moon, newly wrenched from the earth by the impact of a Mars-sized planet, was much closer than at present. Casting a huge shadow across the planet’s face, its pull was such that even the Earth’s crust (which was then less rigid) rose and fell an extraordinary sixty meters twice each day. Wills and Bada do not give an example of the amplitude of the tide at that time, but it must have been truly awesome.
The tides are important to Wills and Bada’s argument both because they are regular and because they possess enormous potential to sort matter. One of the great stumbling blocks to understanding how life might have arisen is the necessarily dilute nature of amino acids in the ancient seas. Unless these building blocks could somehow be concentrated and separated from the chemical chaos surrounding them, there was little prospect that they could interact to create more complex molecules.
Wills and Bada have developed a model that overcomes this difficulty, which they dub “an ancient laboratory on a beach.” As you can see on any beach, tides sort out matter. Here you find a line or cluster of shells, there a line of finer or coarser sand. A beach, with its varying layers of silica and calcium carbonate fragments of differing size and shape, can act as a filter. When that filter is powered by a tide sweeping it twice each day, a beach has the capacity to sort molecules according to size and weight in a highly efficient manner. This process of separating molecules by size and weight is called chromatography—so named because it was first used in the laboratory to separate colored dyes.
Wills and Bada envisage their ancient laboratory on a beach as producing a constantly sifted chemical array. When they reached certain levels in the sand, organic chemicals would become concentrated. Tides might remove some, which the authors envisage as having “died,” while new ones would be washed in and become fixed, thus having been “born” into the chemical community that would ultimately form life. “The result,” they say, “would have been layers of organic molecules that would be constantly growing and changing, increasing in thickness and complexity.” Eventually “the mixture…acquired a definite structure that had been shaped by the ‘birth’ and ‘death’ process” wrought by chromatography and subsequent internal modification.
Here, Wills and Bada controversially claim to have discerned a sort of “proto-Darwinism,” which they nickname “Darwin Lite.” They metaphorically place Darwin where the great biologist himself saw only God at work, writing, “It is Darwin who sped up the origin of life from the primordial soup…and it is Darwin who will aid our efforts to duplicate those events in the laboratory.” If they are correct, then Darwin’s great engine of change partly explains the nonliving as well as the living worlds. This is a major extension of the concept of natural selection, and their argument will doubtless promote a vigorous debate among scientists, most of whom dispute that natural selection can occur in the absence of reproduction, inheritance, or anything that could be called metabolism.
Wills and Bada point out that researchers use two avenues to explore the origins of life, which they characterize as the bottom-up and top-down approaches. They describe these two approaches as “working toward the golden spike” of the creation of life, just as the western and eastern teams of the Union and Central Pacific Railroads did as they raced toward each other, finally meeting on Promontory Summit near Ogden, Utah, on May 10, 1869. It’s a curious analogy, drawn from the American frontier, and as becomes apparent later in their book, the search for life’s origins is intimately tied to the endeavors of the last American frontiersmen, the astronauts of NASA.
The Spark of Life is largely devoted to a discussion of the bottom-up approach, which progresses through experiments such as Miller’s, and through trying to determine from paleontological, astronomical, and chemical studies what the world might have been like at the time that life arose. The top-down approach is conducted via analysis of the chemistry of life, particularly the genetic material contained in all living things. It aims to find the common genetic features shared by all life in order to deter-mine what the original genetic configuration might have been like. Because genetic mutation occurs at a fairly regular rate (giving rise to the so-called molecular clock), the top-downers also hope that by calculating how many mutations have occurred they will be able to pinpoint just when life arose.
At about 11:00 AM on September 28, 1969, the bottom-up school received a gift from the heavens, a sort of Rosetta Stone which fell to earth near the town of Murchison, Victoria, in southern Australia. The Murchison meteorite, as it is now known, is a fragment of a “planetesimal” or small, solid fragment that condensed out of the solar nebula as the solar system formed. Most planetesimals aggregated to form planets, but the Murchison meteorite somehow escaped incorporation. It wandered the void of space for over four billion years until that September day in 1969, when it belatedly became incorporated into planet Earth.
The meteorite comprises 2.5 percent organic matter that is very similar to the organic goo generated by Miller in his experiments. The bottom-up school believe that this demonstrates that “somewhere in the far reaches of space, about 4.5 billion years ago… nature had carried out an experiment almost identical to Miller’s,” though just how this might have occurred remains unclear.
The Murchison meteorite is referred to repeatedly throughout Wills and Bada’s book. Analysis of its chemistry has formed the basis for new experiments, as well as reviving old ideas about how life might have been formed. The fact that when the organic matter from the meteorite is dissolved in water it forms bubbles, for example, has given new life to the idea, first postulated then discarded decades ago, that life might have begun in greasy bubbles which concentrated organic molecules and acted as primitive cell membranes.
So prestigious is the search for life’s origin that The Spark of Life is littered with the names of Nobel laureates, whose contributions are carefully documented, as is their institutional affiliation. Its final chapters concern the search for life beyond Earth. NASA looks set to champion this venture, for Daniel Goldin, its chief administrator, has become an enthusiastic supporter of the search for extraterrestrial life.
NASA is, like the transcontinental railway, a creature of the frontier, and if it is to survive in the current age it must identify green pastures somewhere beyond the known. Increased interest in the search for extraterrestrial life must have seemed like a godsend for the organization.
Many searchers for life beyond Earth seem to be possessed of an almost Panglossian optimism, and since their speculations include the entire universe, their optimism might seem justified; yet Wills and Bada document many earlier hopes that resulted in nothing but disappointment. In the early nineteenth century the moon was widely believed to be inhabited by four-foot-tall humanoids with wings. So convincing were the reports that the women of Boston began planning to contact the moon-dwellers in an attempt to convert them to Christianity. By the early twentieth century the focus had shifted to Mars and its apparently regularly laid out canals. For many Martian life seemed to be a certainty, though curiously, one of the stoutest skeptics of the idea of life on Mars was Alfred Russel Wallace, co-publisher with Darwin of the theory of evolution by natural selection. In 1907 Wallace (who lived a long life) wrote that because of a lack of water, “Mars is not only uninhabited by intelligent beings…but is absolutely UNINHABITABLE.” Only with the Mars landing, and its finding that Martian soil contains a highly reactive element that is apparently inimical to life, have most scientists been won over to Wallace’s view. And yet a few die-hards from NASA hold out, claiming to have found traces of life in a Martian meteorite, a finding now widely disbelieved.
In our own time Venus has been the field of speculation, Carl Sagan suggesting in 1967 that the planet might be inhabited by floating, balloonlike beings; yet closer inspection has made the existence of any life on Venus appear unlikely. Through all of these disproofs, the optimism of the true believers has remained invulnerable. In support of their conviction they quote statisticians who can prove that life must exist somewhere in the vastness of the universe. This debate, incidentally, remains vigorous, with some researchers postulating that millions of planets must support life, while others argue that we are most likely alone. Surely, these skeptics argue, if extraterrestrial life were at all common then the earth would have been colonized from space during its four-billion-year history. The doubters also dispute the value of spending the half-billion dollars that it will cost just to determine whether life exists on the latest frontier of the optimists—below the tens of kilometers of ice that cover Jupiter’s moon Europa.
The skeptics believe that the obsession with finding extraterrestrial life is unwarranted on other grounds, among them how poorly we understand life on our own planet. Steve Jones, in Darwin’s Ghost, does credit to their arguments, for he astonishes the reader with an analysis of life on Earth that makes Sagan’s Venusians look dull. Jones is an unabashed admirer and emulator of Darwin. “The Origin of Species is,” he writes, “without doubt, the book of the millennium… the high point of the literature of fact.” He describes his own work as an attempt “to read Charles Darwin’s mind with the benefit of scientific hindsight.” To do this, Jones uses the structure of Darwin’s Origin, filling out the arguments with modern examples, and reproducing verbatim Darwin’s own summaries of each of the chapters, along with Darwin’s recapitulation and conclusion.
Jones is not one to tolerate the slighting of his hero. We learn that in 1858, when Darwin and Wallace presented their ideas on evolution to the Linnaean Society of London, the society’s president, Thomas Bell, proclaimed that it had been a dull year, not being “marked by any of those striking discoveries which at once revolutionise…the department of science on which they bear.” Jones has made his own inquiries into Bell, describing him as “a dentist with an interest in reptiles” and later as a “reptilian dentist,” who published Kalygonomia, or the Laws of Female Beauty “with plates bound in a separate volume to allow them to be locked away from inquisitive eyes.”
Having disposed of Mr. Bell, Jones informs us that “science (unlike the arts) can be detached from those who do it,” and for that reason he includes the name of no living scientist in his book. Given the author’s adulation of Charles Darwin this is a curious decision, and one which makes it very difficult to track authority in this unreferenced work.
Apparently unafraid of appearing immodest, Jones tells us, “There is no obvious reason why the theory of evolution should attract the finest science writers, but it is so,” and Jones is indeed an entertaining writer, despite having spent thirty years studying snails. At his best he is capable of almost Johnsonian pronouncements, such as “age is a tax on sex, levied by natural selection.” Organization, however, is not his strong card, nor is continuity of argument or full explication of interesting facts. He moves through his material at such a breathtaking pace that the reader can feel that he or she is traversing a field of disconnected if sparkling examples on a runaway horse. Jones’s writing shares some characteristics with that of my favorite eccentric author, John Aubrey, for both are highly entertaining, yet somehow occasionally seem to miss the mark. (In Brief Lives Aubrey glosses William Shakespeare thus: “His father was a Butcher, and…when he was a boy he exercised his father’s Trade, but when he kill’d a calf, he would doe it in a high style, and make a speech… he had but little Latin, and lesse Greeke.”)
Darwin’s Ghost commences with a lambasting of American creationism, then jumps to a discussion of HIV-AIDS, which Jones informs us “contains in its brief history the entire argument of The Origin of Species: variation, a struggle for existence, and natural selection that in time leads to new forms of life.” Then on to the evolution of whales, where he includes a discussion of why Moby Dick was white (“an inherited defect in the ability to make the dark pigment called melanin”) and cetacean retroviruses. Next come our animal companions, where we learn in passing that in Darwin’s England “cats [were] not wholly despised as an article of diet” and that a notorious gang of cat-eaters in West Bromwich meant that fanciers couldn’t “keep a favourite a week.” Then Jones follows Darwin into the arcane world of the pigeon fancier (but not going so far as to join London’s smartest pigeon club, the Philoperisteron, as did Darwin). While a contemporary reader of Darwin lamented that The Origin had not included enough on pigeons (predicting that it “would soon be on every library table” if this section were lengthened), Jones cuts short discussion of the feathered tribes. Instead we get an exceedingly brief treatise on the domestication of wheat, followed by that of dogs. We learn that Linnaeus characterized man’s best friend by its possession of an upturned tail, the fact that it licks its wounds, is often infected with gonorrhea, and frequently urinates upon hearing certain music. Linnaeus clearly knew some strange dogs, among them, Jones informs us, the Naked Dog, the Fat Alco, and the Techichi.
Zoos also receive a cursory examination—“In one, the gorillas were given sausages and a pint of beer for breakfast…. When Philadelphia Zoo opened in 1874, its sloth was poked to death by umbrellas within a week”—in which is included an interesting discussion of how zoo animals respond to the selection imposed by their unnatural environment. Jones makes the point that zoo animals are under intense selective pressure for particular characteristics, not least of which is simply the ability to survive in such an alien environment. Human selective pressure can also be intense, as is made clear by the proliferation of albino tigers (with more than one hundred bred at Cincinnati Zoo alone), all of which are descended from a single male. The albinos are preferred by zookeepers simply because they draw such large crowds. Such selective breeding, along with the propensity of zookeepers to weed out savage, nervous, or intractable individuals, means that zoo animals are rapidly diverging from their wild ancestors.
It is perhaps inevitable that the great mass of material accumulated in Darwin’s Ghost includes some unfortunate errors, which become rather dense when Jones delves into the Southern Hemisphere. He tells us mistakenly that “dogs got to most of the world (except Africa…) as soon as humans did,” ignoring the 50,000-year gap between the arrival of dogs and humans in Australasia. He writes that “South Australia was once covered with a spiny scrub called the jarrah.” This “spiny scrub” is in fact a majestic, nonprickly eucalypt that reaches 135 feet in height and is restricted to high-rainfall areas in southwestern Australia. To state that South African fynbos, Australian kwongan, and Californian chaparral are “fire-resistant” is strange, for they are among the most fire-promoting plant communities known, with fynbos being reduced to little but ash after a blaze. Jones writes wistfully of the lungfish: “Now a mere half dozen kinds are left. They live a dreary existence,…shrouded in mud for much of the year. They are fossils, reminders of a universe now lost.” While it is true that the African and South American lungfish can spend considerable periods shrouded in mud, their Australian relative has no such ability and lives entirely in free water, as did many of its ancient relatives. By the time I reached the false assertions that “the southern beech of South America has close kin in…South Africa,” that “frogs are absent from all oceanic islands,” and that the aquatic form of the axolotl lacks legs, I was becoming skeptical of some of Jones’s more outlandish claims.
Despite its imperfections Darwin’s Ghost has a great deal of material to pique the reader’s interest and challenge the mind. Jones tackles the seemingly intractable problem of the evolution of imitation among butterflies. Some butterflies bear bright markings, which they have evolved as a warning to predators that they are poisonous or distasteful. Various nontoxic species of butterfly have come to imitate their intricate colors. They evidently evolved from well-camouflaged species that must have forsaken their protective coloring. Jones shows that both camouflage and mimicry offer protection, but any intermediate stage seems suicidal. “Quite how the insects traversed the valley of death…is not clear,” he writes with some understatement. In a more homely mood, Jones asks, “Why are twice as many left shoes as right washed ashore in Holland, while the opposite is true for Scottish beaches?” A curious fact indeed, and one for which Wills and Bada’s chromatographic potential of the tides might be invoked, but by this stage I was beginning to doubt whether even Jones’s basic “fact” is correct, and, if it isn’t, we are left with nothing to explain.
Charles Darwin once referred to his mind as “a machine for grinding general laws out of a large collection of facts.” Ever mindful of producing the most robust possible “general laws,” Darwin was careful about the “facts” he fed into his incredible machine, for their veracity was utterly essential to what he was trying to do. Here lies the greatest contrast between Darwin and his “ghostwriter” Jones.
A profound difference also exists between Wills and Bada’s The Spark of Life and Darwin’s The Origin of Species. Despite the fact that Darwin’s work would eventually open the way for removing the divine from the creation of life, nature and all of its creatures are treated with a sense of awe and wonder verging on reverence. “It is interesting to contemplate an entangled bank,” wrote Darwin at the end of his world-changing thesis,
clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us…. There is grandeur in this view of life,…[that] from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
Wills and Bada’s The Spark of Life succeeds admirably in its goal of informing us of the state of research into life’s origin. Jones’s Darwin’s Ghost provides a witty, wide-ranging discourse on natural selection. In the end, however, neither combines erudition with humility and a sense of wonder at the world as Darwin did. Perhaps this is because our human society is becoming ever more like Darwin’s tangled river bank. It’s filling with highly specialized professionals, each capable of doing his or her job spectacularly well, but none able to view life as a whole, and wonder at it.
November 2, 2000