A Short History of Nearly Everything Part 2

CHAPTER 25: DARWIN'S SINGULAR NOTION

IN THE LATE summer or early autumn of 1859, Whitwell Elwin, editor of the respected British journal theQuarterly Review , was sent an advance copy of a new book by the naturalist Charles Darwin. Elwin read the book with interest and agreed that it had merit, but feared that the subject matter was too narrow to attract a wide audience. He urged Darwin to write a book about pigeons instead. Everyone is interested in pigeons, he observed helpfully.Elwin's sage advice was ignored, andOn the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life was published in late November 1859, priced at fifteen s.h.i.+llings. The first edition of 1,250 copies sold out on the first day. It has never been out of print, and scarcely out of controversy, in all the time since-not bad going for a man whose princ.i.p.al other interest was earthworms and who, but for a single impetuous decision to sail around the world, would very probably have pa.s.sed his life as an anonymous country parson known for, well, for an interest in earthworms.Charles Robert Darwin was born on February 12, 1809,[41]in Shrewsbury, a sedate market town in the west Midlands of England. His father was a prosperous and well-regarded physician. His mother, who died when Charles was only eight, was the daughter of Josiah Wedgwood, of pottery fame.Darwin enjoyed every advantage of upbringing, but continually pained his widowed father with his lackl.u.s.ter academic performance. You care for nothing but shooting, dogs, and rat-catching, and you will be a disgrace to yourself and all your family, his father wrote in a line that nearly always appears just about here in any review of Darwin's early life. Although his inclination was to natural history, for his father's sake he tried to study medicine at Edinburgh University but couldn't bear the blood and suffering. The experience of witnessing an operation on an understandably distressed child-this was in the days before anesthetics, of course-left him permanently traumatized. He tried law instead, but found that insupportably dull and finally managed, more or less by default, to acquire a degree in divinity from Cambridge.A life in a rural vicarage seemed to await him when from out of the blue there came a more tempting offer. Darwin was invited to sail on the naval survey s.h.i.+p HMSBeagle, essentially as dinner company for the captain, Robert FitzRoy, whose rank precluded his socializing with anyone other than a gentleman. FitzRoy, who was very odd, chose Darwin in part because he liked the shape of Darwin's nose. (It betokened depth of character, he believed.) Darwin was not FitzRoy's first choice, but got the nod when FitzRoy's preferred companion dropped out. From a twenty-first-century perspective the two men's most striking joint feature was their extreme youthfulness. At the time of sailing, FitzRoy was only twenty-three, Darwin just twenty-two.FitzRoy's formal a.s.signment was to chart coastal waters, but his hobby-pa.s.sion really-was to seek out evidence for a literal, biblical interpretation of creation. That Darwin was trained for the ministry was central to FitzRoy's decision to have him aboard. That Darwin subsequently proved to be not only liberal of view but less than wholeheartedly devoted to Christian fundamentals became a source of lasting friction between them.Darwin's time aboard HMSBeagle, from 1831 to 1836, was obviously the formative experience of his life, but also one of the most trying. He and his captain shared a small cabin, which can't have been easy as FitzRoy was subject to fits of fury followed by spells of simmering resentment. He and Darwin constantly engaged in quarrels, some bordering on insanity, as Darwin later recalled. Ocean voyages tended to become melancholy undertakings at the best of times-the previous captain of theBeagle had put a bullet through his brain during a moment of lonely gloom-and FitzRoy came from a family well known for a depressive instinct. His uncle, Viscount Castlereagh, had slit his throat the previous decade while serving as Chancellor of the Exchequer. (FitzRoy would himself commit suicide by the same method in 1865.) Even in his calmer moods, FitzRoy proved strangely unknowable. Darwin was astounded to learn upon the conclusion of their voyage that almost at once FitzRoy married a young woman to whom he had long been betrothed. In five years in Darwin's company, he had not once hinted at an attachment or even mentioned her name.In every other respect, however, theBeagle voyage was a triumph. Darwin experienced adventure enough to last a lifetime and acc.u.mulated a h.o.a.rd of specimens sufficient to make his reputation and keep him occupied for years. He found a magnificent trove of giant ancient fossils, including the finestMegatherium known to date; survived a lethal earthquake in Chile; discovered a new species of dolphin (which he dutifully namedDelphinus fitzroyi ); conducted diligent and useful geological investigations throughout the Andes; and developed a new and much-admired theory for the formation of coral atolls, which suggested, not coincidentally, that atolls could not form in less than a million years-the first hint of his long-standing attachment to the extreme antiquity of earthly processes. In 1836, aged twenty-seven, he returned home after being away for five years and two days. He never left England again.One thing Darwin didn't do on the voyage was propound the theory (or even a theory) of evolution. For a start, evolution as a concept was already decades old by the 1830s. Darwin's own grandfather, Erasmus, had paid tribute to evolutionary principles in a poem of inspired mediocrity called The Temple of Nature years before Charles was even born. It wasn't until the younger Darwin was back in England and read Thomas Malthus'sEssay on the Principle of Population (which proposed that increases in food supply could never keep up with population growth for mathematical reasons) that the idea began to percolate through his mind that life is a perpetual struggle and that natural selection was the means by which some species prospered while others failed. Specifically what Darwin saw was that all organisms competed for resources, and those that had some innate advantage would prosper and pa.s.s on that advantage to their offspring. By such means would species continuously improve.It seems an awfully simple idea-it is an awfully simple idea-but it explained a great deal, and Darwin was prepared to devote his life to it. How stupid of me not to have thought of it! T. H. Huxley cried upon readingOn the Origin of Species . It is a view that has been echoed ever since.Interestingly, Darwin didn't use the phrase survival of the fittest in any of his work (though he did express his admiration for it). The expression was coined five years after the publication ofOn the Origin of Species by Herbert Spencer inPrinciples of Biology in 1864. Nor did he employ the wordevolution in print until the sixth edition ofOrigin (by which time its use had become too widespread to resist), preferring instead descent with modification. Nor, above all, were his conclusions in any way inspired by his noticing, during his time in the Galapagos Islands, an interesting diversity in the beaks of finches. The story as conventionally told (or at least as frequently remembered by many of us) is that Darwin, while traveling from island to island, noticed that the finches' beaks on each island were marvelously adapted for exploiting local resources-that on one island beaks were st.u.r.dy and short and good for cracking nuts, while on the next island beaks were perhaps long and thin and well suited for winkling food out of crevices-and it was this that set him to thinking that perhaps the birds had not been created this way, but had in a sense created themselves.In fact, the birdshad created themselves, but it wasn't Darwin who noticed it. At the time of theBeagle voyage, Darwin was fresh out of college and not yet an accomplished naturalist and so failed to see that the Galapagos birds were all of a type. It was his friend the ornithologist John Gould who realized that what Darwin had found was lots of finches with different talents. Unfortunately, in his inexperience Darwin had not noted which birds came from which islands. (He had made a similar error with tortoises.) It took years to sort the muddles out.Because of these oversights, and the need to sort through crates and crates of otherBeagle specimens, it wasn't until 1842, six years after his return to England, that Darwin finally began to sketch out the rudiments of his new theory. These he expanded into a 230-page sketch two years later. And then he did an extraordinary thing: he put his notes away and for the next decade and a half busied himself with other matters. He fathered ten children, devoted nearly eight years to writing an exhaustive opus on barnacles (I hate a barnacle as no man ever did before, he sighed, understandably, upon the work's conclusion), and fell prey to strange disorders that left him chronically listless, faint, and flurried, as he put it. The symptoms nearly always included a terrible nausea and generally also incorporated palpitations, migraines, exhaustion, trembling, spots before the eyes, shortness of breath, swimming of the head, and, not surprisingly, depression.The cause of the illness has never been established, but the most romantic and perhaps likely of the many suggested possibilities is that he suffered from Chagas's disease, a lingering tropical malady that he could have acquired from the bite of a Benchuga bug in South America. A more prosaic explanation is that his condition was psychosomatic. In either case, the misery was not. Often he could work for no more than twenty minutes at a stretch, sometimes not that.Much of the rest of his time was devoted to a series of increasingly desperate treatments-icy plunge baths, dousings in vinegar, draping himself with electric chains that subjected him to small jolts of current. He became something of a hermit, seldom leaving his home in Kent, Down House. One of his first acts upon moving to the house was to erect a mirror outside his study window so that he could identify, and if necessary avoid, callers.Darwin kept his theory to himself because he well knew the storm it would cause. In 1844, the year he locked his notes away, a book calledVestiges of the Natural History of Creation roused much of the thinking world to fury by suggesting that humans might have evolved from lesser primates without the a.s.sistance of a divine creator. Antic.i.p.ating the outcry, the author had taken careful steps to conceal his ident.i.ty, which he kept a secret from even his closest friends for the next forty years. Some wondered if Darwin himself might be the author. Others suspected Prince Albert. In fact, the author was a successful and generally una.s.suming Scottish publisher named Robert Chambers whose reluctance to reveal himself had a practical dimension as well as a personal one: his firm was a leading publisher of Bibles.Vestiges was warmly blasted from pulpits throughout Britain and far beyond, but also attracted a good deal of more scholarly ire. TheEdinburgh Review devoted nearly an entire issue-eighty-five pages-to pulling it to pieces. Even T. H. Huxley, a believer in evolution, attacked the book with some venom, unaware that the author was a friend.[42]Darwin's ma.n.u.script might have remained locked away till his death but for an alarming blow that arrived from the Far East in the early summer of 1858 in the form of a packet containing a friendly letter from a young naturalist named Alfred Russel Wallace and the draft of a paper,On the Tendency of Varieties to Depart Indefinitely from the Original Type , outlining a theory of natural selection that was uncannily similar to Darwin's secret jottings. Even some of the phrasing echoed Darwin's own. I never saw a more striking coincidence, Darwin reflected in dismay. If Wallace had my ma.n.u.script sketch written out in 1842, he could not have made a better short abstract.Wallace didn't drop into Darwin's life quite as unexpectedly as is sometimes suggested. The two were already corresponding, and Wallace had more than once generously sent Darwin specimens that he thought might be of interest. In the process of these exchanges Darwin had discreetly warned Wallace that he regarded the subject of species creation as his own territory. This summer will make the 20th year (!) since I opened my first note-book, on the question of how & in what way do species & varieties differ from each other, he had written to Wallace some time earlier. I am now preparing my work for publication, he added, even though he wasn't really.In any case, Wallace failed to grasp what Darwin was trying to tell him, and of course he could have no idea that his own theory was so nearly identical to one that Darwin had been evolving, as it were, for two decades.Darwin was placed in an agonizing quandary. If he rushed into print to preserve his priority, he would be taking advantage of an innocent tip-off from a distant admirer. But if he stepped aside, as gentlemanly conduct arguably required, he would lose credit for a theory that he had independently propounded. Wallace's theory was, by Wallace's own admission, the result of a flash of insight; Darwin's was the product of years of careful, plodding, methodical thought. It was all crus.h.i.+ngly unfair.To compound his misery, Darwin's youngest son, also named Charles, had contracted scarlet fever and was critically ill. At the height of the crisis, on June 28, the child died. Despite the distraction of his son's illness, Darwin found time to dash off letters to his friends Charles Lyell and Joseph Hooker, offering to step aside but noting that to do so would mean that all his work, whatever it may amount to, will be smashed. Lyell and Hooker came up with the compromise solution of presenting a summary of Darwin's and Wallace's ideas together. The venue they settled on was a meeting of the Linnaean Society, which at the time was struggling to find its way back into fas.h.i.+on as a seat of scientific eminence. On July 1, 1858, Darwin's and Wallace's theory was unveiled to the world. Darwin himself was not present. On the day of the meeting, he and his wife were burying their son.The DarwinWallace presentation was one of seven that evening-one of the others was on the flora of Angola-and if the thirty or so people in the audience had any idea that they were witnessing the scientific highlight of the century, they showed no sign of it. No discussion followed. Nor did the event attract much notice elsewhere. Darwin cheerfully later noted that only one person, a Professor Haughton of Dublin, mentioned the two papers in print and his conclusion was that all that was new in them was false, and what was true was old.Wallace, still in the distant East, learned of these maneuverings long after the event, but was remarkably equable and seemed pleased to have been included at all. He even referred to the theory forever after as Darwinism. Much less amenable to Darwin's claim of priority was a Scottish gardener named Patrick Matthew who had, rather remarkably, also come up with the principles of natural selection-in fact, in the very year that Darwin had set sail in theBeagle.Unfortunately, Matthew had published these views in a book calledNaval Timber and Arboriculture , which had been missed not just by Darwin, but by the entire world. Matthew kicked up in a lively manner, with a letter toGardener's Chronicle , when he saw Darwin gaining credit everywhere for an idea that really was his. Darwin apologized without hesitation, though he did note for the record: I think that no one will feel surprised that neither I, nor apparently any other naturalist, has heard of Mr. Matthew's views, considering how briefly they are given, and they appeared in the Appendix to a work on Naval Timber and Arboriculture.Wallace continued for another fifty years as a naturalist and thinker, occasionally a very good one, but increasingly fell from scientific favor by taking up dubious interests such as spiritualism and the possibility of life existing elsewhere in the universe. So the theory became, essentially by default, Darwin's alone.Darwin never ceased being tormented by his ideas. He referred to himself as the Devil's Chaplain and said that revealing the theory felt like confessing a murder. Apart from all else, he knew it deeply pained his beloved and pious wife. Even so, he set to work at once expanding his ma.n.u.script into a book-length work. Provisionally he called itAn Abstract of an Essay on the Origin of Species and Varieties through Natural Selection -a t.i.tle so tepid and tentative that his publisher, John Murray, decided to issue just five hundred copies. But once presented with the ma.n.u.script, and a slightly more arresting t.i.tle, Murray reconsidered and increased the initial print run to 1,250.On the Origin of Specieswas an immediate commercial success, but rather less of a critical one. Darwin's theory presented two intractable difficulties. It needed far more time than Lord Kelvin was willing to concede, and it was scarcely supported by fossil evidence. Where, asked Darwin's more thoughtful critics, were the transitional forms that his theory so clearly called for? If new species were continuously evolving, then there ought to be lots of intermediate forms scattered across the fossil record, but there were not.[43]In fact, the record as it existed then (and for a long time afterward) showed no life at all right up to the moment of the famous Cambrian explosion.But now here was Darwin, without any evidence, insisting that the earlier seasmust have had abundant life and that we just hadn't found it yet because, for whatever reason, it hadn't been preserved. It simply could not be otherwise, Darwin maintained. The case at present must remain inexplicable; and may be truly urged as a valid argument against the views here entertained, he allowed most candidly, but he refused to entertain an alternative possibility. By way of explanation he speculated-inventively but incorrectly-that perhaps the Precambrian seas had been too clear to lay down sediments and thus had preserved no fossils.Even Darwin's closest friends were troubled by the blitheness of some of his a.s.sertions. Adam Sedgwick, who had taught Darwin at Cambridge and taken him on a geological tour of Wales in 1831, said the book gave him more pain than pleasure. Louis Aga.s.siz dismissed it as poor conjecture. Even Lyell concluded gloomily: Darwin goes too far.T. H. Huxley disliked Darwin's insistence on huge amounts of geological time because he was a saltationist, which is to say a believer in the idea that evolutionary changes happen not gradually but suddenly. Saltationists (the word comes from the Latin for leap) couldn't accept that complicated organs could ever emerge in slow stages. What good, after all, is one-tenth of a wing or half an eye? Such organs, they thought, only made sense if they appeared in a finished state.The belief was surprising in as radical a spirit as Huxley because it closely recalled a very conservative religious notion first put forward by the English theologian William Paley in 1802 and known as argument from design. Paley contended that if you found a pocket watch on the ground, even if you had never seen such a thing before, you would instantly perceive that it had been made by an intelligent ent.i.ty. So it was, he believed, with nature: its complexity was proof of its design. The notion was a powerful one in the nineteenth century, and it gave Darwin trouble too. The eye to this day gives me a cold shudder, he acknowledged in a letter to a friend. In theOrigin he conceded that it seems, I freely confess, absurd in the highest possible degree that natural selection could produce such an instrument in gradual steps.Even so, and to the unending exasperation of his supporters, Darwin not only insisted that all change was gradual, but in nearly every edition ofOrigin he stepped up the amount of time he supposed necessary to allow evolution to progress, which pushed his ideas increasingly out of favor. Eventually, according to the scientist and historian Jeffrey Schwartz, Darwin lost virtually all the support that still remained among the ranks of fellow natural historians and geologists.Ironically, considering that Darwin called his bookOn the Origin of Species , the one thing he couldn't explain was how species originated. Darwin's theory suggested a mechanism for how a species might become stronger or better or faster-in a word, fitter-but gave no indication of how it might throw up a new species. A Scottish engineer, Fleeming Jenkin, considered the problem and noted an important flaw in Darwin's argument. Darwin believed that any beneficial trait that arose in one generation would be pa.s.sed on to subsequent generations, thus strengthening the species.Jenkin pointed out that a favorable trait in one parent wouldn't become dominant in succeeding generations, but in fact would be diluted through blending. If you pour whiskey into a tumbler of water, you don't make the whiskey stronger, you make it weaker. And if you pour that dilute solution into another gla.s.s of water, it becomes weaker still. In the same way, any favorable trait introduced by one parent would be successively watered down by subsequent matings until it ceased to be apparent at all. Thus Darwin's theory was not a recipe for change, but for constancy. Lucky flukes might arise from time to time, but they would soon vanish under the general impulse to bring everything back to a stable mediocrity. If natural selection were to work, some alternative, unconsidered mechanism was required.Unknown to Darwin and everyone else, eight hundred miles away in a tranquil corner of Middle Europe a retiring monk named Gregor Mendel was coming up with the solution.Mendel was born in 1822 to a humble farming family in a backwater of the Austrian empire in what is now the Czech Republic. Schoolbooks once portrayed him as a simple but observant provincial monk whose discoveries were largely serendipitous-the result of noticing some interesting traits of inheritance while pottering about with pea plants in the monastery's kitchen garden. In fact, Mendel was a trained scientist-he had studied physics and mathematics at the Olmutz Philosophical Inst.i.tute and the University of Vienna-and he brought scientific discipline to all he did. Moreover, the monastery at Brno where he lived from 1843 was known as a learned inst.i.tution. It had a library of twenty thousand books and a tradition of careful scientific investigation.Before embarking on his experiments, Mendel spent two years preparing his control specimens, seven varieties of pea, to make sure they bred true. Then, helped by two full-time a.s.sistants, he repeatedly bred and crossbred hybrids from thirty thousand pea plants. It was delicate work, requiring them to take the most exacting pains to avoid accidental cross-fertilization and to note every slight variation in the growth and appearance of seeds, pods, leaves, stems, and flowers. Mendel knew what he was doing.He never used the wordgene -it wasn't coined until 1913, in an English medical dictionary-though he did invent the termsdominant andrecessive . What he established was that every seed contained two factors or elemente, as he called them-a dominant one and a recessive one-and these factors, when combined, produced predictable patterns of inheritance.The results he converted into precise mathematical formulae. Altogether Mendel spent eight years on the experiments, then confirmed his results with similar experiments on flowers, corn, and other plants. If anything, Mendel wastoo scientific in his approach, for when he presented his findings at the February and March meetings of the Natural History Society of Brno in 1865, the audience of about forty listened politely but was conspicuously unmoved, even though the breeding of plants was a matter of great practical interest to many of the members.When Mendel's report was published, he eagerly sent a copy to the great Swiss botanist Karl-Wilhelm von Nageli, whose support was more or less vital for the theory's prospects. Unfortunately, Nageli failed to perceive the importance of what Mendel had found. He suggested that Mendel try breeding hawkweed. Mendel obediently did as Nageli suggested, but quickly realized that hawkweed had none of the requisite features for studying heritability. It was evident to him that Nageli had not read the paper closely, or possibly at all. Frustrated, Mendel retired from investigating heritability and spent the rest of his life growing outstanding vegetables and studying bees, mice, and sunspots, among much else. Eventually he was made abbot.Mendel's findings weren't quite as widely ignored as is sometimes suggested. His study received a glowing entry in theEncyclopaedia Britannica -then a more leading record of scientific thought than now-and was cited repeatedly in an important paper by the German Wilhelm Olbers Focke. Indeed, it was because Mendel's ideas never entirely sank below the waterline of scientific thought that they were so easily recovered when the world was ready for them.Together, without realizing it, Darwin and Mendel laid the groundwork for all of life sciences in the twentieth century. Darwin saw that all living things are connected, that ultimately they trace their ancestry to a single, common source, while Mendel's work provided the mechanism to explain how that could happen. The two men could easily have helped each other. Mendel owned a German edition of theOrigin of Species , which he is known to have read, so he must have realized the applicability of his work to Darwin's, yet he appears to have made no effort to get in touch. And Darwin for his part is known to have studied Focke's influential paper with its repeated references to Mendel's work, but didn't connect them to his own studies.The one thing everyone thinks featured in Darwin's argument, that humans are descended from apes, didn't feature at all except as one pa.s.sing allusion. Even so, it took no great leap of imagination to see the implications for human development in Darwin's theories, and it became an immediate talking point.The showdown came on Sat.u.r.day, June 30, 1860, at a meeting of the British a.s.sociation for the Advancement of Science in Oxford. Huxley had been urged to attend by Robert Chambers, author ofVestiges of the Natural History of Creation , though he was still unaware of Chambers's connection to that contentious tome. Darwin, as ever, was absent. The meeting was held at the Oxford Zoological Museum. More than a thousand people crowded into the chamber; hundreds more were turned away. People knew that something big was going to happen, though they had first to wait while a slumber-inducing speaker named John William Draper of New York University bravely slogged his way through two hours of introductory remarks on The Intellectual Development of Europe Considered with Reference to the Views of Mr. Darwin.Finally, the Bishop of Oxford, Samuel Wilberforce, rose to speak. Wilberforce had been briefed (or so it is generally a.s.sumed) by the ardent anti-Darwinian Richard Owen, who had been a guest in his home the night before. As nearly always with events that end in uproar, accounts vary widely on what exactly transpired. In the most popular version, Wilberforce, when properly in flow, turned to Huxley with a dry smile and demanded of him whether he claimed attachment to the apes by way of his grandmother or grandfather. The remark was doubtless intended as a quip, but it came across as an icy challenge. According to his own account, Huxley turned to his neighbor and whispered, The Lord hath delivered him into my hands, then rose with a certain relish.Others, however, recalled a Huxley trembling with fury and indignation. At all events, Huxley declared that he would rather claim kins.h.i.+p to an ape than to someone who used his eminence to propound uninformed twaddle in what was supposed to be a serious scientific forum. Such a riposte was a scandalous impertinence, as well as an insult to Wilberforce's office, and the proceedings instantly collapsed in tumult. A Lady Brewster fainted. Robert FitzRoy, Darwin's companion on theBeagle twenty-five years before, wandered through the hall with a Bible held aloft, shouting, The Book, the Book. (He was at the conference to present a paper on storms in his capacity as head of the newly created Meteorological Department.) Interestingly, each side afterward claimed to have routed the other.Darwin did eventually make his belief in our kins.h.i.+p with the apes explicit inThe Descent of Man in 1871. The conclusion was a bold one since nothing in the fossil record supported such a notion. The only known early human remains of that time were the famous Neandertal bones from Germany and a few uncertain fragments of jawbones, and many respected authorities refused to believe even in their antiquity.The Descent of Man was altogether a more controversial book, but by the time of its appearance the world had grown less excitable and its arguments caused much less of a stir.For the most part, however, Darwin pa.s.sed his twilight years with other projects, most of which touched only tangentially on questions of natural selection. He spent amazingly long periods picking through bird droppings, scrutinizing the contents in an attempt to understand how seeds spread between continents, and spent years more studying the behavior of worms. One of his experiments was to play the piano to them, not to amuse them but to study the effects on them of sound and vibration. He was the first to realize how vitally important worms are to soil fertility. It may be doubted whether there are many other animals which have played so important a part in the history of the world, he wrote in his masterwork on the subject,The Formation of Vegetable Mould Through the Action of Worms (1881), which was actually more popular thanOn the Origin of Specieshad ever been. Among his other books wereOn the Various Contrivances by Which British and Foreign Orchids Are Fertilised by Insects (1862),Expressions of the Emotions in Man and Animals (1872), which sold almost 5,300 copies on its first day,The Effects of Cross and Self Fertilization in the Vegetable Kingdom (1876)-a subject that came improbably close to Mendel's own work, without attaining anything like the same insights-and his last book,The Power of Movement in Plants . Finally, but not least, he devoted much effort to studying the consequences of inbreeding-a matter of private interest to him. Having married his own cousin, Darwin glumly suspected that certain physical and mental frailties among his children arose from a lack of diversity in his family tree.Darwin was often honored in his lifetime, but never forOn the Origin of Species orDescent of Man. When the Royal Society bestowed on him the prestigious Copley Medal it was for his geology, zoology, and botany, not evolutionary theories, and the Linnaean Society was similarly pleased to honor Darwin without embracing his radical notions. He was never knighted, though he was buried in Westminster Abbey-next to Newton. He died at Down in April 1882. Mendel died two years later.Darwin's theory didn't really gain widespread acceptance until the 1930s and 1940s, with the advance of a refined theory called, with a certain hauteur, the Modern Synthesis, combining Darwin's ideas with those of Mendel and others. For Mendel, appreciation was also posthumous, though it came somewhat sooner. In 1900, three scientists working separately in Europe rediscovered Mendel's work more or less simultaneously. It was only because one of them, a Dutchman named Hugo de Vries, seemed set to claim Mendel's insights as his own that a rival made it noisily clear that the credit really lay with the forgotten monk.The world was almost ready, but not quite, to begin to understand how we got here-how we made each other. It is fairly amazing to reflect that at the beginning of the twentieth century, and for some years beyond, the best scientific minds in the world couldn't actually tell you where babies came from.And these, you may recall, were men who thought science was nearly at an end.

CHAPTER 26: THE STUFF OF LIFE

IF YOUR TWO parents hadn't bonded just when they did-possibly to the second, possibly to the nanosecond-you wouldn't be here. And if their parents hadn't bonded in a precisely timely manner, you wouldn't be here either. And if their parents hadn't done likewise, and their parents before them, and so on, obviously and indefinitely, you wouldn't be here.Push backwards through time and these ancestral debts begin to add up. Go back just eight generations to about the time that Charles Darwin and Abraham Lincoln were born, and already there are over 250 people on whose timely couplings your existence depends. Continue further, to the time of Shakespeare and theMayflower Pilgrims, and you have no fewer than 16,384 ancestors earnestly exchanging genetic material in a way that would, eventually and miraculously, result in you.At twenty generations ago, the number of people procreating on your behalf has risen to 1,048,576. Five generations before that, and there are no fewer than 33,554,432 men and women on whose devoted couplings your existence depends. By thirty generations ago, your total number of forebears-remember, these aren't cousins and aunts and other incidental relatives, but only parents and parents of parents in a line leading ineluctably to you-is over one billion (1,073,741,824, to be precise). If you go back sixty-four generations, to the time of the Romans, the number of people on whose cooperative efforts your eventual existence depends has risen to approximately 1,000,000,000,000,000,000, which is several thousand times the total number of people who have ever lived.Clearly something has gone wrong with our math here. The answer, it may interest you to learn, is that your line is not pure. You couldn't be here without a little incest-actually quite a lot of incest-albeit at a genetically discreet remove. With so many millions of ancestors in your background, there will have been many occasions when a relative from your mother's side of the family procreated with some distant cousin from your father's side of the ledger. In fact, if you are in a partners.h.i.+p now with someone from your own race and country, the chances are excellent that you are at some level related. Indeed, if you look around you on a bus or in a park or cafe or any crowded place,most of the people you see are very probably relatives. When someone boasts to you that he is descended from William the Conqueror or theMayflower Pilgrims, you should answer at once: Me, too! In the most literal and fundamental sense we are all family.We are also uncannily alike. Compare your genes with any other human being's and on average they will be about 99.9 percent the same. That is what makes us a species. The tiny differences in that remaining 0.1 percent-roughly one nucleotide base in every thousand, to quote the British geneticist and recent n.o.bel laureate John Sulston-are what endow us with our individuality. Much has been made in recent years of the unraveling of the human genome. In fact, there is no such thing as the human genome. Every human genome is different. Otherwise we would all be identical. It is the endless recombinations of our genomes-each nearly identical, but not quite-that make us what we are, both as individuals and as a species.But what exactly is this thing we call the genome? And what, come to that, are genes? Well, start with a cell again. Inside the cell is a nucleus, and inside each nucleus are the chromosomes-forty-six little bundles of complexity, of which twenty-three come from your mother and twenty-three from your father. With a very few exceptions, every cell in your body-99.999 percent of them, say-carries the same complement of chromosomes. (The exceptions are red blood cells, some immune system cells, and egg and sperm cells, which for various organizational reasons don't carry the full genetic package.) Chromosomes const.i.tute the complete set of instructions necessary to make and maintain you and are made of long strands of the little wonder chemical called deoxyribonucleic acid or DNA-the most extraordinary molecule on Earth, as it has been called.DNA exists for just one reason-to create more DNA-and you have a lot of it inside you: about six feet of it squeezed into almost every cell. Each length of DNA comprises some 3.2 billion letters of coding, enough to provide 103,480,000,000possible combinations, guaranteed to be unique against all conceivable odds, in the words of Christian de Duve. That's a lot of possibility-a one followed by more than three billion zeroes. It would take more than five thousand average-size books just to print that figure, notes de Duve. Look at yourself in the mirror and reflect upon the fact that you are beholding ten thousand trillion cells, and that almost every one of them holds two yards of densely compacted DNA, and you begin to appreciate just how much of this stuff you carry around with you. If all your DNA were woven into a single fine strand, there would be enough of it to stretch from the Earth to the Moon and back not once or twice but again and again. Altogether, according to one calculation, you may have as much as twenty million kilometers of DNA bundled up inside you.Your body, in short, loves to make DNA and without it you couldn't live. Yet DNA is not itself alive. No molecule is, but DNA is, as it were, especially unalive. It is among the most nonreactive, chemically inert molecules in the living world, in the words of the geneticist Richard Lewontin. That is why it can be recovered from patches of long-dried blood or s.e.m.e.n in murder investigations and coaxed from the bones of ancient Neandertals. It also explains why it took scientists so long to work out how a substance so mystifyingly low key-so, in a word, lifeless-could be at the very heart of life itself.As a known ent.i.ty, DNA has been around longer than you might think. It was discovered as far back as 1869 by Johann Friedrich Miescher, a Swiss scientist working at the University of Tubingen in Germany. While delving microscopically through the pus in surgical bandages, Miescher found a substance he didn't recognize and called it nuclein (because it resided in the nuclei of cells). At the time, Miescher did little more than note its existence, but nuclein clearly remained on his mind, for twenty-three years later in a letter to his uncle he raised the possibility that such molecules could be the agents behind heredity. This was an extraordinary insight, but one so far in advance of the day's scientific requirements that it attracted no attention at all.For most of the next half century the common a.s.sumption was that the material-now called deoxyribonucleic acid, or DNA-had at most a subsidiary role in matters of heredity. It was too simple. It had just four basic components, called nucleotides, which was like having an alphabet of just four letters. How could you possibly write the story of life with such a rudimentary alphabet? (The answer is that you do it in much the way that you create complex messages with the simple dots and dashes of Morse code-by combining them.) DNA didn't do anything at all, as far as anyone could tell. It just sat there in the nucleus, possibly binding the chromosome in some way or adding a splash of acidity on command or fulfilling some other trivial task that no one had yet thought of. The necessary complexity, it was thought, had to exist in proteins in the nucleus.There were, however, two problems with dismissing DNA. First, there was so much of it: two yards in nearly every nucleus, so clearly the cells esteemed it in some important way. On top of this, it kept turning up, like the suspect in a murder mystery, in experiments. In two studies in particular, one involving thePneumonococcus bacterium and another involving bacteriophages (viruses that infect bacteria), DNA betrayed an importance that could only be explained if its role were more central than prevailing thought allowed. The evidence suggested that DNA was somehow involved in the making of proteins, a process vital to life, yet it was also clear that proteins were being madeoutside the nucleus, well away from the DNA that was supposedly directing their a.s.sembly.No one could understand how DNA could possibly be getting messages to the proteins. The answer, we now know, was RNA, or ribonucleic acid, which acts as an interpreter between the two. It is a notable oddity of biology that DNA and proteins don't speak the same language. For almost four billion years they have been the living world's great double act, and yet they answer to mutually incompatible codes, as if one spoke Spanish and the other Hindi. To communicate they need a mediator in the form of RNA. Working with a kind of chemical clerk called a ribosome, RNA translates information from a cell's DNA into terms proteins can understand and act upon.However, by the early 1900s, where we resume our story, we were still a very long way from understanding that, or indeed almost anything else to do with the confused business of heredity.Clearly there was a need for some inspired and clever experimentation, and happily the age produced a young person with the diligence and apt.i.tude to undertake it. His name was Thomas Hunt Morgan, and in 1904, just four years after the timely rediscovery of Mendel's experiments with pea plants and still almost a decade beforegene would even become a word, he began to do remarkably dedicated things with chromosomes.Chromosomes had been discovered by chance in 1888 and were so called because they readily absorbed dye and thus were easy to see under the microscope. By the turn of the twentieth century it was strongly suspected that they were involved in the pa.s.sing on of traits, but no one knew how, or even really whether, they did this.Morgan chose as his subject of study a tiny, delicate fly formally calledDrosophila melanogaster , but more commonly known as the fruit fly (or vinegar fly, banana fly, or garbage fly).Drosophila is familiar to most of us as that frail, colorless insect that seems to have a compulsive urge to drown in our drinks. As laboratory specimens fruit flies had certain very attractive advantages: they cost almost nothing to house and feed, could be bred by the millions in milk bottles, went from egg to productive parenthood in ten days or less, and had just four chromosomes, which kept things conveniently simple.Working out of a small lab (which became known inevitably as the Fly Room) in Schermerhorn Hall at Columbia University in New York, Morgan and his team embarked on a program of meticulous breeding and crossbreeding involving millions of flies (one biographer says billions, though that is probably an exaggeration), each of which had to be captured with tweezers and examined under a jeweler's gla.s.s for any tiny variations in inheritance. For six years they tried to produce mutations by any means they could think of-zapping the flies with radiation and X-rays, rearing them in bright light and darkness, baking them gently in ovens, spinning them crazily in centrifuges-but nothing worked. Morgan was on the brink of giving up when there occurred a sudden and repeatable mutation-a fly that had white eyes rather than the usual red ones. With this breakthrough, Morgan and his a.s.sistants were able to generate useful deformities, allowing them to track a trait through successive generations. By such means they could work out the correlations between particular characteristics and individual chromosomes, eventually proving to more or less everyone's satisfaction that chromosomes were at the heart of inheritance.The problem, however, remained the next level of biological intricacy: the enigmatic genes and the DNA that composed them. These were much trickier to isolate and understand. As late as 1933, when Morgan was awarded a n.o.bel Prize for his work, many researchers still weren't convinced that genes even existed. As Morgan noted at the time, there was no consensus as to what the genes are-whether they are real or purely fict.i.tious. It may seem surprising that scientists could struggle to accept the physical reality of something so fundamental to cellular activity, but as Wallace, King, and Sanders point out inBiology: The Science of Life (that rarest thing: a readable college text), we are in much the same position today with mental processes such as thought and memory. We know that we have them, of course, but we don't know what, if any, physical form they take. So it was for the longest time with genes. The idea that you could pluck one from your body and take it away for study was as absurd to many of Morgan's peers as the idea that scientists today might capture a stray thought and examine it under a microscope.What was certainly true was thatsomething a.s.sociated with chromosomes was directing cell replication. Finally, in 1944, after fifteen years of effort, a team at the Rockefeller Inst.i.tute in Manhattan, led by a brilliant but diffident Canadian named Oswald Avery, succeeded with an exceedingly tricky experiment in which an innocuous strain of bacteria was made permanently infectious by crossing it with alien DNA, proving that DNA was far more than a pa.s.sive molecule and almost certainly was the active agent in heredity. The Austrian-born biochemist Erwin Chargaff later suggested quite seriously that Avery's discovery was worth two n.o.bel Prizes.Unfortunately, Avery was opposed by one of his own colleagues at the inst.i.tute, a strong-willed and disagreeable protein enthusiast named Alfred Mirsky, who did everything in his power to discredit Avery's work-including, it has been said, lobbying the authorities at the Karolinska Inst.i.tute in Stockholm not to give Avery a n.o.bel Prize. Avery by this time was sixty-six years old and tired. Unable to deal with the stress and controversy, he resigned his position and never went near a lab again. But other experiments elsewhere overwhelmingly supported his conclusions, and soon the race was on to find the structure of DNA.Had you been a betting person in the early 1950s, your money would almost certainly have been on Linus Pauling of Caltech, America's leading chemist, to crack the structure of DNA. Pauling was unrivaled in determining the architecture of molecules and had been a pioneer in the field of X-ray crystallography, a technique that would prove crucial to peering into the heart of DNA. In an exceedingly distinguished career, he would win two n.o.bel Prizes (for chemistry in 1954 and peace in 1962), but with DNA he became convinced that the structure was a triple helix, not a double one, and never quite got on the right track. Instead, victory fell to an unlikely quartet of scientists in England who didn't work as a team, often weren't on speaking terms, and were for the most part novices in the field.Of the four, the nearest to a conventional boffin was Maurice Wilkins, who had spent much of the Second World War helping to design the atomic bomb. Two of the others, Rosalind Franklin and Francis Crick, had pa.s.sed their war years working on mines for the British government-Crick of the type that blow up, Franklin of the type that produce coal.The most unconventional of the foursome was James Watson, an American prodigy who had distinguished himself as a boy as a member of a highly popular radio program calledThe Quiz Kids (and thus could claim to be at least part of the inspiration for some of the members of the Gla.s.s family inFranny and Zooey and other works by J. D. Salinger) and who had entered the University of Chicago aged just fifteen. He had earned his Ph.D. by the age of twenty-two and was now attached to the famous Cavendish Laboratory in Cambridge. In 1951, he was a gawky twenty-three-year-old with a strikingly lively head of hair that appears in photographs to be straining to attach itself to some powerful magnet just out of frame.Crick, twelve years older and still without a doctorate, was less memorably hirsute and slightly more tweedy. In Watson's account he is presented as bl.u.s.tery, nosy, cheerfully argumentative, impatient with anyone slow to share a notion, and constantly in danger of being asked to go elsewhere. Neither was formally trained in biochemistry.Their a.s.sumption was that if you could determine the shape of a DNA molecule you would be able to see-correctly, as it turned out-how it did what it did. They hoped to achieve this, it would appear, by doing as little work as possible beyond thinking, and no more of that than was absolutely necessary. As Watson cheerfully (if a touch disingenuously) remarked in his autobiographical bookThe Double Helix , It was my hope that the gene might be solved without my learning any chemistry. They weren't actually a.s.signed to work on DNA, and at one point were ordered to stop it. Watson was ostensibly mastering the art of crystallography; Crick was supposed to be completing a thesis on the X-ray diffraction of large molecules.Although Crick and Watson enjoy nearly all the credit in popular accounts for solving the mystery of DNA, their breakthrough was crucially dependent on experimental work done by their compet.i.tors, the results of which were obtained fortuitously, in the tactful words of the historian Lisa Jardine. Far ahead of them, at least at the beginning, were two academics at King's College in London, Wilkins and Franklin.The New Zealandborn Wilkins was a retiring figure, almost to the point of invisibility. A 1998 PBS doc.u.mentary on the discovery of the structure of DNA-a feat for which he shared the 1962 n.o.bel Prize with Crick and Watson-managed to overlook him entirely.The most enigmatic character of all was Franklin. In a severely unflattering portrait, Watson inThe Double Helix depicted Franklin as a woman who was unreasonable, secretive, chronically uncooperative, and-this seemed especially to irritate him-almost willfully uns.e.xy. He allowed that she was not unattractive and might have been quite stunning had she taken even a mild interest in clothes, but in this she disappointed all expectations. She didn't even use lipstick, he noted in wonder, while her dress sense showed all the imagination of English blue-stocking adolescents.[44]However, she did have the best images in existence of the possible structure of DNA, achieved by means of X-ray crystallography, the technique perfected by Linus Pauling. Crystallography had been used successfully to map atoms in crystals (hence crystallography), but DNA molecules were a much more finicky proposition. Only Franklin was managing to get good results from the process, but to Wilkins's perennial exasperation she refused to share her findings.If Franklin was not warmly forthcoming with her findings, she cannot be altogether blamed. Female academics at King's in the 1950s were treated with a formalized disdain that dazzles modern sensibilities (actually any sensibilities). However senior or accomplished, they were not allowed into the college's senior common room but instead had to take their meals in a more utilitarian chamber that even Watson conceded was dingily pokey. On top of this she was being constantly pressed-at times actively hara.s.sed-to share her results with a trio of men whose desperation to get a peek at them was seldom matched by more engaging qualities, like respect. I'm afraid we always used to adopt-let's say a patronizing att.i.tude toward her, Crick later recalled. Two of these men were from a competing inst.i.tution and the third was more or less openly siding with them. It should hardly come as a surprise that she kept her results locked away.That Wilkins and Franklin did not get along was a fact that Watson and Crick seem to have exploited to their benefit. Although Crick and Watson were trespa.s.sing rather unashamedly on Wilkins's territory, it was with them that he increasingly sided-not altogether surprisingly since Franklin herself was beginning to act in a decidedly queer way. Although her results showed that DNA definitely was helical in shape, she insisted to all that it was not. To Wilkins's presumed dismay and embarra.s.sment, in the summer of 1952 she posted a mock notice around the King's physics department that said: It is with great regret that we have to announce the death, on Friday 18th July 1952 of D.N.A. helix. . . . It is hoped that Dr. M.H.F. Wilkins will speak in memory of the late helix.The outcome of all this was that in January 1953, Wilkins showed Watson Franklin's images, apparently without her knowledge or consent. It would be an understatement to call it a significant help. Years later Watson conceded that it was the key event . . . it mobilized us. Armed with the knowledge of the DNA molecule's basic shape and some important elements of its dimensions, Watson and Crick redoubled their efforts. Everything now seemed to go their way. At one point Pauling was en route to a conference in England at which he would in all likelihood have met with Wilkins and learned enough to correct the misconceptions that had put him on the wrong line of inquiry, but this was the McCarthy era and Pauling found himself detained at Idlewild Airport in New York, his pa.s.sport confiscated, on the grounds that he was too liberal of temperament to be allowed to travel abroad. Crick and Watson also had the no less convenient good fortune that Pauling's son was working at the Cavendish and innocently kept them abreast of any news of developments and setbacks at home.Still facing the possibility of being trumped at any moment, Watson and Crick applied themselves feverishly to the problem. It was known that DNA had four chemical components-called adenine, guanine, cytosine, and thiamine-and that these paired up in particular ways. By playing with pieces of cardboard cut into the shapes of molecules, Watson and Crick were able to work out how the pieces fit together. From this they made a Meccano-like model-perhaps the most famous in modern science-consisting of metal plates bolted together in a spiral, and invited Wilkins, Franklin, and the rest of the world to have a look. Any informed person could see at once that they had solved the problem. It was without question a brilliant piece of detective work, with or without the boost of Franklin's picture.The April 25, 1953, edition ofNature carried a 900-word article by Watson and Crick t.i.tled A Structure for Deoxyribose Nucleic Acid. Accompanying it were separate articles by Wilkins and Franklin. It was an eventful time in the world-Edmund Hillary was just about to clamber to the top of Everest while Elizabeth II was imminently to be crowned queen of England-so the discovery of the secret of life was mostly overlooked. It received a small mention in theNews Chronicle and was ignored elsewhere.Rosalind Franklin did not share in the n.o.bel Prize. She died of ovarian cancer at the age of just thirty-seven in 1958, four years before the award was granted. n.o.bel Prizes are not awarded posthumously. The cancer almost certainly arose as a result of chronic overexposure to X-rays through her work and needn't have happened. In her much-praised 2002 biography of Franklin, Brenda Maddox noted that Franklin rarely wore a lead ap.r.o.n and often stepped carelessly in front of a beam. Oswald Avery never won a n.o.bel Prize either and was also largely overlooked by posterity, though he did at least have the satisfaction of living just long enough to see his findings vindicated. He died in 1955.Watson and Crick's discovery wasn't actually confirmed until the 1980s. As Crick said in one of his books: It took over twenty-five years for our model of DNA to go from being only rather plausible, to being very plausible . . . and from there to being virtually certainly correct.Even so, with the structure of DNA understood progress in genetics was swift, and by 1968 the journalScience could run an article t.i.tled That Was the Molecular Biology That Was, suggesting-it hardly seems possible, but it is so-that the work of genetics was nearly at an end.In fact, of course, it was only just beginning. Even now there is a great deal about DNA that we scarcely understand, not least why so much of it doesn't actually seem todo anything. Ninety-seven percent of your DNA consists of nothing but long stretches of meaningless garble-junk, or non-coding DNA, as biochemists prefer to put it. Only here and there along each strand do you find sections that control and organize vital functions. These are the curious and long-elusive genes.Genes are nothing more (nor less) than instructions to make proteins. This they do with a certain dull fidelity. In this sense, they are rather like the keys of a piano, each playing a single note and nothing else, which is obviously a trifle monotonous. But combine the genes, as you would combine piano keys, and you can create chords and melodies of infinite variety. Put all these genes together, and you have (to continue the metaphor) the great symphony of existence known as the human genome.An alternative and more common way to regard the genome is as a kind of instruction manual for the body. Viewed this way, the chromosomes can be imagined as the book's chapters and the genes as individual instructions for making proteins. The words in which the instructions are written are called codons, and the letters are known as bases. The bases-the letters of the genetic alphabet-consist of the four nucleotides mentioned a page or two back: adenine, thiamine, guanine, and cytosine. Despite the importance of what they do, these substances are not made of anything exotic. Guanine, for instance, is the same stuff that abounds in, and gives its name to, guano.The shape of a DNA molecule, as everyone knows, is rather like a spiral staircase or twisted rope ladder: the famous double helix. The uprights of this structure are made of a type of sugar called deoxyribose, and the whole of the helix is a nucleic acid-hence the name deoxyribonucleic acid. The rungs (or steps) are formed by two bases joining across the s.p.a.ce between, and they can combine in only two ways: guanine is always paired with cytosine and thiamine always with adenine. The order in which these letters appear as you move up or down the ladder const.i.tutes the DNA code; logging it has been the job of the Human Genome Project.Now the particular brilliance of DNA lies in its manner of replication. When it is time to produce a new DNA molecule, the two strands part down the middle, like the zipper on a jacket, and each half goes off to form a new partners.h.i.+p. Because each nucleotide along a strand pairs up with a specific other nucleotide, each strand serves as a template for the creation of a new matching strand. If you possessed just one strand of your own DNA, you could easily enough reconstruct the matching side by working out the necessary partners.h.i.+ps: if the topmost rung on one strand was made of guanine, then you would know that the topmost rung on the matching strand must be cytosine. Work your way down the ladder through all the nucleotide pairings, and eventually you would have the code for a new molecule. That is just what happens in nature, except that nature does it really quickly-in only a matter of seconds, which is quite a feat.Most of the time our DNA replicates with dutiful accuracy, but just occasionally-about one time in a million-a letter gets into the wrong place. This is known as a single nucleotide polymorphism, or SNP, familiarly known to biochemists as a Snip. Generally these Snips are buried in stretches of noncoding DNA and have no detectable consequence for the body. But occasionally they make a difference. They might leave you predisposed to some disease, but equally they might confer some slight advantage-more protective pigmentation, for instance, or increased production of red blood cells for someone living at alt.i.tude. Over time, these slight modifications acc.u.mulate in both individuals and in populations, contributing to the distinctiveness of both.The balance between accuracy and errors in replication is a fine one. Too many errors and the organism can't function, but too few and it sacrifices adaptability. A similar balance must exist between stability in an organism and innovation. An increase in red blood cells can help a person or group living at high elevations to move and breathe more easily because more red cells can carry more oxygen. But additional red cells also thicken the blood. Add too many, and it's like pumping oil, in the words of Temple University anthropologist Charles Weitz. That's hard on the heart. Thus those designed to live at high alt.i.tude get increased breathing efficiency, but pay for it with higher-risk hearts. By such means does Darwinian natural selection look after us. It also helps to explain why we are all so similar. Evolution simply won't let you become too different-not without becoming a new species anyway.The 0.1 percent difference between your genes and mine is accounted for by our Snips. Now if you compared your DNA with a third person's, there would also be 99.9 percent correspondence, but the Snips would, for the most part, be in different places. Add more people to the comparison and you will get yet more Snips in yet more places. For every one of your 3.2 billion bases, somewhere on the planet there will be a person, or group of persons, with different coding in that position. So not only is it wrong to refer to the human genome, but in a sense we don't even have a human genome. We have six billion of them. We are all 99.9 percent the same, but equally, in the words of the biochemist David c.o.x, you could say all humans share nothing, and that would be correct, too.But we have still to explain why so little of that DNA has any discernible purpose. It starts to get a little unnerving, but it does really seem that the purpose of life is to perpetuate DNA. The 97 percent of our DNA commonly called junk is largely made up of clumps of letters that, in Ridley's words, exist for the pure and simple reason that they are good at getting themselves duplicated.[45]Most of your DNA, in other words, is not devoted to you but to itself: you are a machine for reproducing it, not it for you. Life, you will recall, just wants to be, and DNA is what makes it so.Even when DNA includes instructions for making genes-when it codes for them, as scientists put it-it is not necessarily with the smooth functioning of the organism in mind. One of the commonest genes we have is for a protein called reverse transcriptase, which has no known beneficial function in human beings at all. The one thing itdoesdo is make it possible for retroviruses, such as the AIDS virus, to slip unnoticed into the human system.In other words, our bodies devote considerable energies to producing a protein that does nothing that is beneficial and sometimes clobbers us. Our bodies have no choice but to do so because the genes order it. We are vessels for their whims. Altogether, almost half of human genes-the largest proportion yet found in any organism-don't do anything at all, as far as we can tell, except reproduce themselves.All organisms are in some sense slaves to their genes. That's why salmon and spiders and other types of creatures more or less beyond counting are prepared to die in the process of mating. The desire to breed, to disperse one's genes, is the most powerful impulse in nature. As Sherwin B. Nuland has put it: Empires fall, ids explode, great symphonies are written, and behind all of it is a single instinct that demands satisfaction. From an evolutionary point of view, s.e.x is really just a reward mechanism to encourage us to pa.s.s on our genetic material.Scientists had only barely absorbed the surprising news that most of our DNA doesn't do anything when even more unexpected findings began to turn up. First in Germany and then in Switzerland researchers performed some rather bizarre experiments that produced curiously unbizarre outcomes. In one they took the gene that controlled the development of a mouse's eye and inserted it into the larva of a fruit fly. The thought was that it might produce something interestingly grotesque. In fact, the mouse-eye gene not only made a viable eye in the fruit fly, it made afly's eye. Here were two creatures that hadn't shared a common ancestor for 500 million years, yet could swap genetic material as if they were sisters.The story was the same wherever researchers looked. They found that they could insert human DNA into certain cells of flies, and the flies would accept it as if it were their own. Over 60 percent of human genes, it turns out, are fundamentally the same as those found in fruit flies. At least 90 percent correlate at some level to those found in mice. (We even have the same genes for making a tail, if only they would switch on.) In field after field, researchers found that whatever organism they were working on-