CHAPTER 30: GOOD-BYE

IN THE EARLY 1680s, at just about the time that Edmond Halley and his friends Christopher Wren and Robert Hooke were settling down in a London coffeehouse and embarking on the casual wager that would result eventually in Isaac Newton’sPrincipia , Henry Cavendish’s weighing of the Earth, and many of the other inspired and commendable undertakings that have occupied us for much of the past four hundred pages, a rather less desirable milestone was being passed on the island of Mauritius, far out in the Indian Ocean some eight hundred miles off the east coast of Madagascar.

There, some forgotten sailor or sailor’s pet was harrying to death the last of the dodos, the famously flightless bird whose dim but trusting nature and lack of leggy zip made it a rather irresistible target for bored young tars on shore leave. Millions of years of peaceful isolation had not prepared it for the erratic and deeply unnerving behavior of human beings.

We don’t know precisely the circumstances, or even year, attending the last moments of the last dodo, so we don’t know which arrived first, a world that contained aPrincipia or one that had no dodos, but we do know that they happened at more or less the same time. You would be hard pressed, I would submit, to find a better pairing of occurrences to illustrate the divine and felonious nature of the human being—a species of organism that is capable of unpicking the deepest secrets of the heavens while at the same time pounding into extinction, for no purpose at all, a creature that never did us any harm and wasn’t even remotely capable of understanding what we were doing to it as we did it. Indeed, dodos were so spectacularly short on insight, it is reported, that if you wished to find all the dodos in a vicinity you had only to catch one and set it to squawking, and all the others would waddle along to see what was up.

The indignities to the poor dodo didn’t end quite there. In 1755, some seventy years after the last dodo’s death, the director of the Ashmolean Museum in Oxford decided that the institution’s stuffed dodo was becoming unpleasantly musty and ordered it tossed on a bonfire. This was a surprising decision as it was by this time the only dodo in existence, stuffed or otherwise. A passing employee, aghast, tried to rescue the bird but could save only its head and part of one limb.

As a result of this and other departures from common sense, we are not now entirely sure what a living dodo was like. We possess much less information than most people suppose—a handful of crude descriptions by “unscientific voyagers, three or four oil paintings, and a few scattered osseous fragments,” in the somewhat aggrieved words of the nineteenth-century naturalist H. E. Strickland. As Strickland wistfully observed, we have more physical evidence of some ancient sea monsters and lumbering saurapods than we do of a bird that lived into modern times and required nothing of us to survive except our absence.

So what is known of the dodo is this: it lived on Mauritius, was plump but not tasty, and was the biggest-ever member of the pigeon family, though by quite what margin is unknown as its weight was never accurately recorded. Extrapolations from Strickland’s “osseous fragments” and the Ashmolean’s modest remains show that it was a little over two and a half feet tall and about the same distance from beak tip to backside. Being flightless, it nested on the ground, leaving its eggs and chicks tragically easy prey for pigs, dogs, and monkeys brought to the island by outsiders. It was probably extinct by 1683 and was most certainly gone by 1693. Beyond that we know almost nothing except of course that we will not see its like again. We know nothing of its reproductive habits and diet, where it ranged, what sounds it made in tranquility or alarm. We don’t possess a single dodo egg.

From beginning to end our acquaintance with animate dodos lasted just seventy years. That is a breathtakingly scanty period—though it must be said that by this point in our history we did have thousands of years of practice behind us in the matter of irreversible eliminations. Nobody knows quite how destructive human beings are, but it is a fact that over the last fifty thousand years or so wherever we have gone animals have tended to vanish, in often astonishingly large numbers.

In America, thirty genera of large animals—some very large indeed—disappeared practically at a stroke after the arrival of modern humans on the continent between ten and twenty thousand years ago. Altogether North and South America between them lost about three quarters of their big animals once man the hunter arrived with his flint-headed spears and keen organizational capabilities. Europe and Asia, where the animals had had longer to evolve a useful wariness of humans, lost between a third and a half of their big creatures. Australia, for exactly the opposite reasons, lost no less than 95 percent.

Because the early hunter populations were comparatively small and the animal populations truly monumental—as many as ten million mammoth carcasses are thought to lie frozen in the tundra of northern Siberia alone—some authorities think there must be other explanations, possibly involving climate change or some kind of pandemic. As Ross MacPhee of the American Museum of Natural History put it: “There’s no material benefit to hunting dangerous animals more often than you need to—there are only so many mammoth steaks you can eat.” Others believe it may have been almost criminally easy to catch and clobber prey. “In Australia and the Americas,” says Tim Flannery, “the animals probably didn’t know enough to run away.”

Some of the creatures that were lost were singularly spectacular and would take a little managing if they were still around. Imagine ground sloths that could look into an upstairs window, tortoises nearly the size of a small Fiat, monitor lizards twenty feet long basking beside desert highways in Western Australia. Alas, they are gone and we live on a much diminished planet. Today, across the whole world, only four types of really hefty (a metric ton or more) land animals survive: elephants, rhinos, hippos, and giraffes. Not for tens of millions of years has life on Earth been so diminutive and tame.

The question that arises is whether the disappearances of the Stone Age and disappearances of more recent times are in effect part of a single extinction event—whether, in short, humans are inherently bad news for other living things. The sad likelihood is that we may well be. According to the University of Chicago paleontologist David Raup, the background rate of extinction on Earth throughout biological history has been one species lost every four years on average. According to one recent calculation, human-caused extinction now may be running as much as 120,000 times that level.

In the mid-1990s, the Australian naturalist Tim Flannery, now head of the South Australian Museum in Adelaide, became struck by how little we seemed to know about many extinctions, including relatively recent ones. “Wherever you looked, there seemed to be gaps in the records—pieces missing, as with the dodo, or not recorded at all,” he told me when I met him in Melbourne a year or so ago.

Flannery recruited his friend Peter Schouten, an artist and fellow Australian, and together they embarked on a slightly obsessive quest to scour the world’s major collections to find out what was lost, what was left, and what had never been known at all. They spent four years picking through old skins, musty specimens, old drawings, and written descriptions—whatever was available. Schouten made life-sized paintings of every animal they could reasonably re-create, and Flannery wrote the words. The result was an extraordinary book calledA Gap in Nature , constituting the most complete—and, it must be said, moving—catalog of animal extinctions from the last three hundred years.

For some animals, records were good, but nobody had done anything much with them, sometimes for years, sometimes forever. Steller’s sea cow, a walrus-like creature related to the dugong, was one of the last really big animals to go extinct. It was truly enormous—an adult could reach lengths of nearly thirty feet and weigh ten tons—but we are acquainted with it only because in 1741 a Russian expedition happened to be shipwrecked on the only place where the creatures still survived in any numbers, the remote and foggy Commander Islands in the Bering Sea.

Happily, the expedition had a naturalist, Georg Steller, who was fascinated by the animal. “He took the most copious notes,” says Flannery. “He even measured the diameter of its whiskers. The only thing he wouldn’t describe was the male genitals—though, for some reason, he was happy enough to do the female’s. He even saved a piece of skin, so we had a good idea of its texture. We weren’t always so lucky.”

The one thing Steller couldn’t do was save the sea cow itself. Already hunted to the brink of extinction, it would be gone altogether within twenty-seven years of Steller’s discovery of it. Many other animals, however, couldn’t be included because too little is known about them. The Darling Downs hopping mouse, Chatham Islands swan, Ascension Island flightless crake, at least five types of large turtle, and many others are forever lost to us except as names.

A great deal of extinction, Flannery and Schouten discovered, hasn’t been cruel or wanton, but just kind of majestically foolish. In 1894, when a lighthouse was built on a lonely rock called Stephens Island, in the tempestuous strait between the North and South Islands of New Zealand, the lighthouse keeper’s cat kept bringing him strange little birds that it had caught. The keeper dutifully sent some specimens to the museum in Wellington. There a curator grew very excited because the bird was a relic species of flightless wrens—the only example of a flightless perching bird ever found anywhere. He set off at once for the island, but by the time he got there the cat had killed them all. Twelve stuffed museum species of the Stephens Island flightless wren are all that now exist.

At least we have those. All too often, it turns out, we are not much better at looking after species after they have gone than we were before they went. Take the case of the lovely Carolina parakeet. Emerald green, with a golden head, it was arguably the most striking and beautiful bird ever to live in North America—parrots don’t usually venture so far north, as you may have noticed—and at its peak it existed in vast numbers, exceeded only by the passenger pigeon. But the Carolina parakeet was also considered a pest by farmers and easily hunted because it flocked tightly and had a peculiar habit of flying up at the sound of gunfire (as you would expect), but then returning almost at once to check on fallen comrades.

In his classicAmerican Omithology , written in the early nineteenth century, Charles Willson Peale describes an occasion in which he repeatedly empties a shotgun into a tree in which they roost:

At each successive discharge, though showers of them fell, yet the affection of the survivors seemed rather to increase; for, after a few circuits around the place, they again alighted near me, looking down on their slaughtered companions with such manifest symptoms of sympathy and concern, as entirely disarmed me.

By the second decade of the twentieth century, the birds had been so relentlessly hunted that only a few remained alive in captivity. The last one, named Inca, died in the Cincinnati Zoo in 1918 (not quite four years after the last passenger pigeon died in the same zoo) and was reverently stuffed. And where would you go to see poor Inca now? Nobody knows. The zoo lost it.

What is both most intriguing and puzzling about the story above is that Peale was a lover of birds, and yet did not hesitate to kill them in large numbers for no better reason than that it interested him to do so. It is a truly astounding fact that for the longest time the people who were most intensely interested in the world’s living things were the ones most likely to extinguish them.

No one represented this position on a larger scale (in every sense) than Lionel Walter Rothschild, the second Baron Rothschild. Scion of the great banking family, Rothschild was a strange and reclusive fellow. He lived his entire life in the nursery wing of his home at Tring, in Buckinghamshire, using the furniture of his childhood—even sleeping in his childhood bed, though eventually he weighed three hundred pounds.

His passion was natural history and he became a devoted accumulator of objects. He sent hordes of trained men—as many as four hundred at a time—to every quarter of the globe to clamber over mountains and hack their way through jungles in the pursuit of new specimens—particularly things that flew. These were crated or boxed up and sent back to Rothschild’s estate at Tring, where he and a battalion of assistants exhaustively logged and analyzed everything that came before them, producing a constant stream of books, papers, and monographs—some twelve hundred in all. Altogether, Rothschild’s natural history factory processed well over two million specimens and added five thousand species of creature to the scientific archive.

Remarkably, Rothschild’s collecting efforts were neither the most extensive nor the most generously funded of the nineteenth century. That title almost certainly belongs to a slightly earlier but also very wealthy British collector named Hugh Cuming, who became so preoccupied with accumulating objects that he built a large oceangoing ship and employed a crew to sail the world full-time, picking up whatever they could find—birds, plants, animals of all types, and especially shells. It was his unrivaled collection of barnacles that passed to Darwin and served as the basis for his seminal study.

However, Rothschild was easily the most scientific collector of his age, though also the most regrettably lethal, for in the 1890s he became interested in Hawaii, perhaps the most temptingly vulnerable environment Earth has yet produced. Millions of years of isolation had allowed Hawaii to evolve 8,800 unique species of animals and plants. Of particular interest to Rothschild were the islands’ colorful and distinctive birds, often consisting of very small populations inhabiting extremely specific ranges.

The tragedy for many Hawaiian birds was that they were not only distinctive, desirable, and rare—a dangerous combination in the best of circumstances—but also often heartbreakingly easy to take. The greater koa finch, an innocuous member of the honeycreeper family, lurked shyly in the canopies of koa trees, but if someone imitated its song it would abandon its cover at once and fly down in a show of welcome. The last of the species vanished in 1896, killed by Rothschild’s ace collector Harry Palmer, five years after the disappearance of its cousin the lesser koa finch, a bird so sublimely rare that only one has ever been seen: the one shot for Rothschild’s collection. Altogether during the decade or so of Rothschild’s most intensive collecting, at least nine species of Hawaiian birds vanished, but it may have been more.

Rothschild was by no means alone in his zeal to capture birds at more or less any cost. Others in fact were more ruthless. In 1907 when a well-known collector named Alanson Bryan realized that he had shot the last three specimens of black mamos, a species of forest bird that had only been discovered the previous decade, he noted that the news filled him with “joy.”

It was, in short, a difficult age to fathom—a time when almost any animal was persecuted if it was deemed the least bit intrusive. In 1890, New York State paid out over one hundred bounties for eastern mountain lions even though it was clear that the much-harassed creatures were on the brink of extinction. Right up until the 1940s many states continued to pay bounties for almost any kind of predatory creature. West Virginia gave out an annual college scholarship to whoever brought in the most dead pests—and “pests” was liberally interpreted to mean almost anything that wasn’t grown on farms or kept as pets.

Perhaps nothing speaks more vividly for the strangeness of the times than the fate of the lovely little Bachman’s warbler. A native of the southern United States, the warbler was famous for its unusually thrilling song, but its population numbers, never robust, gradually dwindled until by the 1930s the warbler vanished altogether and went unseen for many years. Then in 1939, by happy coincidence two separate birding enthusiasts, in widely separated locations, came across lone survivors just two days apart. They both shot the birds, and that was the last that was ever seen of Bachman’s warblers.

The impulse to exterminate was by no means exclusively American. In Australia, bounties were paid on the Tasmanian tiger (properly the thylacine), a doglike creature with distinctive “tiger” stripes across its back, until shortly before the last one died, forlorn and nameless, in a private Hobart zoo in 1936. Go to the Tasmanian Museum today and ask to see the last of this species—the only large carnivorous marsupial to live into modern times—and all they can show you are photographs. The last surviving thylacine was thrown out with the weekly trash.

I mention all this to make the point that if you were designing an organism to look after life in our lonely cosmos, to monitor where it is going and keep a record of where it has been, you wouldn’t choose human beings for the job.

But here’s an extremely salient point: we have been chosen, by fate or Providence or whatever you wish to call it. As far as we can tell, we are the best there is. We may be all there is. It’s an unnerving thought that we may be the living universe’s supreme achievement and its worst nightmare simultaneously.

Because we are so remarkably careless about looking after things, both when alive and when not, we have no idea—really none at all—about how many things have died off permanently, or may soon, or may never, and what role we have played in any part of the process. In 1979, in the bookThe Sinking Ark , the author Norman Myers suggested that human activities were causing about two extinctions a week on the planet. By the early 1990s he had raised the figure to some six hundred per week. (That’s extinctions of all types—plants, insects, and so on as well as animals.) Others have put the figure even higher—to well over a thousand a week. A United Nations report of 1995, on the other hand, put the total number of known extinctions in the last four hundred years at slightly under 500 for animals and slightly over 650 for plants—while allowing that this was “almost certainly an underestimate,” particularly with regard to tropical species. A few interpreters think most extinction figures are grossly inflated.

The fact is, we don’t know. Don’t have any idea. We don’t know when we started doing many of the things we’ve done. We don’t know what we are doing right now or how our present actions will affect the future. What we do know is that there is only one planet to do it on, and only one species of being capable of making a considered difference. Edward O. Wilson expressed it with unimprovable brevity inThe Diversity of Life : “One planet, one experiment.”

If this book has a lesson, it is that we are awfully lucky to be here—and by “we” I mean every living thing. To attain any kind of life in this universe of ours appears to be quite an achievement. As humans we are doubly lucky, of course: We enjoy not only the privilege of existence but also the singular ability to appreciate it and even, in a multitude of ways, to make it better. It is a talent we have only barely begun to grasp.

We have arrived at this position of eminence in a stunningly short time. Behaviorally modern human beings—that is, people who can speak and make art and organize complex activities—have existed for only about 0.0001 percent of Earth’s history. But surviving for even that little while has required a nearly endless string of good fortune.

We really are at the beginning of it all. The trick, of course, is to make sure we never find the end. And that, almost certainly, will require a good deal more than lucky breaks.

REFERENCES

References

*A word on scientific notation: Since very large numbers are cumbersome to write and nearly impossible to read, scientists use a shorthand involving powers (or multiples) of ten in which, for instance, 10,000,000,000 is written 1010 and 6,500,000 becomes 6.5 x 106. The principle is based very simply on multiples of ten: 10 x 10 (or 100) becomes 102; 10 x 10 x 10 (or 1,000) is 103; and so on, obviously and indefinitely. The little superscript number signifies the number of zeroes following the larger principal number. Negative notations provide latter in print (especially essentially a mirror image, with the superscript number indicating the number of spaces to the right of the decimal point (so 10-4 means 0.0001). Though I salute the principle, it remains an amazement to me that anyone seeing “1.4 x 109 km3’ would see at once that that signifies 1.4 billion cubic kilometers, and no less a wonder that they would choose the former over the in a book designed for the general reader, where the example was found. On the assumption that many general readers are as unmathematical as I am, I will use them sparingly, though they are occasionally unavoidable, not least in a chapter dealing with things on a cosmic scale.

[†]Properly called the Opik-Oort cloud, it is named for the Estonian astronomer Ernst Opik, who hypothesized its existence in 1932, and for the Dutch astronomer Jan Oort, who refined the calculations eighteen years later.

* Triangulation, their chosen method, was a popular technique based on the geometric fact that if you know the length of one side of a triangle and the angles of two corners, you can work out all its other dimensions without leaving your chair. Suppose, by way of example, that you and I decided we wished to know how far it is to the Moon. Using triangulation, the first thing we must do is put some distance between us, so let’s say for argument that you stay in Paris and I go to Moscow and we both look at the Moon at the same time. Now if you imagine a line connecting the three principals of this exercise-that is, you and I and the Moon-it forms a triangle. Measure the length of the baseline between you and me and the angles of our two corners and the rest can be simply calculated. (Because the interior angles of a triangle always add up to 180 degrees, if you know the sum of two of the angles you can instantly calculate the third; and knowing the precise shape of a triangle and the length of one side tells you the lengths of the other sides.) This was in fact the method use by a Greek astronomer, Hipparchus of Nicaea, in 150 B.C. to work out the Moon’s distance from Earth. At ground level, the principles of triangulation are the same, except that the triangles don’t reach into space but rather are laid side to side on a map. In measuring a degree of meridian, the surveyors would create a sort of chain of triangles marching across the landscape.

[4]How fast you are spinning depends on where you are. The speed of the Earth’s spin varies from a little over 1,000 miles an hour at the equator to 0 at the poles.

[5]The next transit will be on June 8, 2004, with a second in 2012. There were none in the twentieth century.

[6]In 1781 Herschel became the first person in the modern era to discover a planet. He wanted to call it George, after the British monarch, but was overruled. Instead it became Uranus.

[7]To a physicist, mass and weight are two quite different things. Your mass stays the same wherever you go, but your weight varies depending on how far you are from the center of some other massive object like a planet. Travel to the Moon and you will be much lighter but no less massive. On Earth, for all practical purposes, mass and weight are the same and so the terms can be treated as synonymous. at least outside the classroom.

[8]There will be no testing here, but if you are ever required to memorize them you might wish to remember John Wilford’s helpful advice to think of the eras (Precambrian, Paleozoic, Mesozoic, an( Cenozoic) as seasons in a year and the periods (Permian, Triassic Jurassic, etc.) as the months.

[9]Although virtually all books find a space for him, there is a striking variability in the details associated with Ussher. Some books say he made his pronouncement in 1650, others in 1654, still others in 1664. Many cite the date of Earth’s reputed beginning as October 26. At least one book of note spells his name “Usher.” The matter is interestingly surveyed in Stephen Jay Gould’s Eight Little Piggies.

[10]Darwin loved an exact number. In a later work, he announced that the number of worms to be found in an average acre of English country soil was 53,767.

[11]In particular he elaborated the Second Law of Thermodynamics. A discussion of these laws would be a book in itself, but I offer here this crisp summation by the chemist P. W Atkins, just to provide a sense of them: “There are four Laws. The third of them, the Second Law, was recognized first; the first, the Zeroth Law, was formulated last; the First Law was second; the Third Law might not even be a law in the same sense as the others.” In briefest terms, the second la\\ states that a little energy is always wasted. You can’t have a perpetual motion device because no matter how efficient, it will always lose energy and eventually run down. The first law says that you can’t create energy and the third that you can’t reduce temperatures to absolute zero; there will always be some residual warmth. As Dennis Overbye notes, the three principal laws are sometimes expressed jocularly as (1) you can’t win, (2) you can’t break even, and (3) you can’t get out of the game.

[12]The notable exception being the Tyrannosaurus rex, which was found by Barnum Brown in 1902.

[13]The confusion over the aluminum/aluminium spelling arose b cause of some uncharacteristic indecisiveness on Davy’s part. When he first isolated the element in 1808, he called italumium . For son reason he thought better of that and changed it toaluminum four years later. Americans dutifully adopted the new term, but mai British users dislikedaluminum , pointing out that it disrupted the -ium pattern established by sodium, calcium, and strontium, so they added a vowel and syllable.

[14]The principle led to the much later adoption of Avogadro’s number, a basic unit of measure in chemistry, which was named for Avogadro long after his death. It is the number of molecules found in 2.016 grams of hydrogen gas (or an equal volume of any other gas). Its value is placed at 6.0221367 x 1023, which is an enormously large number. Chemistry students have long amused themselves by computing just how large a number it is, so I can report that it is equivalent to the number of popcorn kernels needed to cover the United States to a depth of nine miles, or cupfuls of water in the Pacific Ocean, or soft drink cans that would, evenly stacked, cover the Earth to a depth of 200 miles. An equivalent number of American pennies would be enough to make every person on Earth a dollar trillionaire. It is a big number.

[15]Specifically it is a measure of randomness or disorder in a system. Darrell Ebbing, in the textbookGeneral Chemistry, very usefully suggests thinking of a deck of cards. A new pack fresh out of the box, arranged by suit and in sequence from ace to king, can be said to be in its ordered state. Shuffle the cards and you put them in a disordered state. Entropy is a way of measuring just how disordered that state is and of determining the likelihood of particular outcomes with further shuffles. Of course, if you wish to have any observations published in a respectable journal you will need also to understand additional concepts such as thermal nonuniformities, lattice distances, and stoichiometric relationships, but that’s the general idea.

[16]Planck was often unlucky in life. His beloved first wife died early, in 1909, and the younger of his two sons was killed in the First World War. He also had twin daughters whom he adored. One died giving birth. The surviving twin went to look after the baby and fell in love with her sister’s husband. They married and two years later she died in childbirth. In 1944, when Planck was eighty-five, an Allied bomb fell on his house and he lost everything-papers, diaries, a lifetime of accumulations. The following year his surviving son was caught in a conspiracy to assassinate Hitler and executed.

[17]Einstein was honored, somewhat vaguely, “for services to theoretical physics.” He had to wait sixteen years, till 1921, to receive the award-quite a long time, all things considered, but nothing at all compared with Frederick Reines, who detected the neutrino in 1957 but wasn’t honored with a Nobel until 1995, thirty-eight years later, or the German Ernst Ruska, who invented the electron microscope in 1932 and received his Nobel Prize in 1986, more than half a century after the fact. Since Nobel Prizes are never awarded posthumously, longevity can be as important a factor as ingenuity for prizewinners.

[18]Howc came to be the symbol for the speed of light is something of a mystery, but David Bodanis suggests it probably came from the Latinceleritas , meaning swiftness. The relevant volume of theOxford English Dictionary , compiled a decade before Einstein’s theory, recognizesc as a symbol for many things, from carbon to cricket, but makes no mention of it as a symbol for light or swiftness.

[19]Named for Johann Christian Doppler, an Austrian physicist, who first noticed the effect in 1842. Briefly, what happens is that as a moving object approaches a stationary one its sound waves become bunched up as they cram up against whatever device is receiving them (your ears, say), just as you would expect of anything that is being pushed from behind toward an immobile object. This bunching is perceived by the listener as a kind of pinched and elevated sound (the yee). As the sound source passes, the sound waves spread out and lengthen, causing the pitch to drop abruptly (the yummm).

[20]The name comes from the same Cavendishes who producec Henry. This one was William Cavendish, seventh Duke of Devonshire, who was a gifted mathematician and steel baron in Victoriar England. In 1870, he gave the university £6,300 to build an experimental lab.

[21]Geiger would also later become a loyal Nazi, unhesitatingly betraying Jewish colleagues, including many who had helped him.

[22]There is a littleuncertainty about the use of the word uncertainty in regard to Heisenberg’s principle. Michael Frayn, in an afterword to his playCopenhagen , notes that several words in German-Unsicherheit, Unscharfe, Unbestimmtheit-have been used by various translators, but that none quite equates to the English uncertainty. Frayn suggests thatindeterminacy would be a better word for the principle andindeterminability would be better still.

[23]Or at least that is how it is nearly always rendered. The actual quote was: “It seems hard to sneak a look at God’s cards. But that He plays dice and uses ‘telepathic’ methods. . . is something that I cannot believe for a single moment.”

[24]If you have ever wondered how the atoms determine which 50 percent will die and which 50 percent will survive for the next session, the answer is that the half-life is really just a statistical convenience-a kind of actuarial table for elemental things. Imagine you had a sample of material with a half-life of 30 seconds. It isn’t that every atom in the sample will exist for exactly 30 seconds or 60 seconds or 90 seconds or some other tidily ordained period. Each atom will in fact survive for an entirely random length of time that has nothing to do with multiples of 30; it might last until two seconds from now or it might oscillate away for years or decades or centuries to come. No one can say. But what we can say is that for the sample as a whole the rate of disappearance will be such that half the atoms will disappear every 30 seconds. It’s an average rate, in other words, and you can apply it to any large sampling. Someone once worked out, for instance, that dimes have a half-life of about 30 years.

[25]There are practical side effects to all this costly effort. The World Wide Web is a CERN offshoot. It was invented by a CERN scientist, Tim Berners-Lee, in 1989.

[26]You are of course entitled to wonder what is meant exactly by “a constant of 50″ or “a constant of 100.” The answer lies in astronomical units of measure. Except conversationally, astronomers don’t use light-years. They use a distance called theparsec (a contraction ofparallax andsecond ), based on a universal measure called the stellar parallax and equivalent to 3.26 light-years. Really big measures, like the size of a universe, are measured in megaparsecs: a million parsecs. The constant is expressed in terms of kilometers per second per megaparsec. Thus when astronomers refer to a Hubble constant of 50, what they really mean is “50 kilometers per second per megaparsec.” For most of us that is of course an utterly meaningless measure, but then with astronomical measures most distances are so huge as to be utterly meaningless.

[27]It is KT rather than CT because C had already been appropriated forCambrian. Depending on which source you credit, the K comes either from the GreekKreta or GermanKreide . Both conveniently mean “chalk,” which is also whatCretaceous means.

[28]For those who crave a more detailed picture of the Earth’s interior, here are the dimensions of the various layers, using average figures: From 0 to 40 km (25 mi) is the crust. From 40 to 400 km (25 to 250 mi) is the upper mantle. From 400 to 650 km (250 to 400 mi) is a transition zone between the upper and lower mantle. From 650 to 2,700 km (400 to 1,700 mi) is the lower mantle. From 2,700 to 2,890 km (1,700 to 1,900 mi) is the “D” layer. From 2,890 to 5,150 km (1,900 to 3,200 mi) is the outer core, and from 5,150 to 6,378 km (3,200 to 3,967 mi) is the inner core.

[29]The discovery of extremophiles in the boiling mudpots of Yellowstone and similar organisms found elsewhere made scientists realize that actually life of a type could range much farther than that-even, perhaps, beneath the icy skin of Pluto. What we are talking about here are the conditions that would produce reasonably complex surface creatures.

[30]Of the remaining four, three are nitrogen and the remaining atom is divided among all the other elements.

[31]Oxygen itself is not combustible; it merely facilitates the combus tion of other things. This is just as well, for if oxygen were corn bustible, each time you lit a match all the air around you would bur into flame. Hydrogen gas, on the other hand, is extremely corn bustible, as the dirigibleHindenburg demonstrated on May 6, 193 in Lakehurst, New Jersey, when its hydrogen fuel burst explosive) into flame, killing thirty-six people.

[32]If you have ever been struck by how beautifully crisp and well defined the edges of cumulus clouds tend to be, while other clouds are more blurry, the explanation is that in a cumulus cloud there is a pronounced boundary between the moist interior of the cloud and the dry air beyond it. Any water molecule that strays beyond the edge of the cloud is immediately zapped by the dry air beyond, allowing the cloud to keep its fine edge. Much higher cirrus clouds are composed of ice, and the zone between the edge of the cloud and the air beyond is not so clearly delineated, which is why they tend to be blurry at the edges.

[33]The term means a number of things to different people, it appears. In November 2002, Carl Wunsch of MIT published a report inScience , “What Is the Thermohaline Circulation?,” in which he noted that the expression has been used in leading journals to signify at least seven different phenomena (circulation at the abyssal level, circulation driven by differences in density or buoyancy, “meridional overturning circulation of mass,” and so on)-though all have to do with ocean circulations and the transfer of heat, the cautiously vague and embracing sense in which I have employed it here.

[34]The indigestible parts of giant squid, in particular their beaks, accumulate in sperm whales’ stomachs into the substance known as ambergris, which is used as a fixative in perfumes. The next time you spray on Chanel No. 5 (assuming you do), you may wish to reflect that you are dousing yourself in distillate of unseen sea monster.

[35]There are actually twenty-two naturally occurring amino acids known on Earth, and more may await discovery, but only twenty of them are necessary to produce us and most other living things. The twenty-second, called pyrrolysine, was discovered in 2002 by researchers at Ohio State University and is found only in a single type of archaean (a basic form of life that we will discuss a little further on in the story) calledMethanosarcina barkeri .

[36]To illustrate, humans are in the domain eucarya, in the kingdom animalia, in the phylum chordata, in the subphylum vertebrata, in the class mammalia, in the order primates, in the family hominidae, in the genus homo, in the speciessapiens . (The convention, I’m informed, is to italicize genus and species names, but not those of higher divisions.) Some taxonomists employ further subdivisions: tribe, suborder, infraorder, parvorder, and more.

[37]The formal word for a zoological category, such asphylum orgenus . The plural istaxa .

[38]We are actually getting worse at some matters of hygiene. Dr. Maunder believes that the move toward low-temperature washing machine detergents has encouraged bugs to proliferate. As he puts it: “If you wash lousy clothing at low temperatures, all you get is cleaner lice.”

[39]Actually, quite a lot of cells are lost in the process of development, so the number you emerge with is really just a guess. Depending on which source you consult the number can vary by several orders of magnitude. The figure of ten thousand trillion (or quadrillion) is from Margulis and Sagan, 1986.

[40]Leeuwenhoek was close friends with another Delft notable, the artist Jan Vermeer. In the mid-1660s, Vermeer, who previously had been a competent but not outstanding artist, suddenly developed the mastery of light and perspective for which he has been celebrated ever since. Though it has never been proved, it has long been suspected that he used a camera obscura, a device for projecting images onto a flat surface through a lens. No such device was listed among Vermeer’s personal effects after his death, but it happens that the executor of Vermeer’s estate was none other than Antoni van Leeuwenhoek, the most secretive lens-maker of his day.

[41]An auspicious date in history: on the same day in Kentucky, Abraham Lincoln was born.

[42]Darwin was one of the few to guess correctly. He happened to be visiting Chambers one day when an advance copy of the sixth edition of Vestiges was delivered. The keenness with which Chambers checked the revisions was something of a giveaway, though it appears the two men did not discuss it.

[43]By coincidence, in 1861, at the height of the controversy, just such evidence turned up when workers in Bavaria found the bones of an ancient archaeopteryx, a creature halfway between a bird and a dinosaur. (It had feathers, but it also had teeth.) It was an impressive and helpful find, and its significance much debated, but a single discovery could hardly be considered conclusive.

[44]In 1968, Harvard University Press canceled publication ofThe Double Helix after Crick and Wilkins complained about its characterizations, which the science historian Lisa Jardine has described as “gratuitously hurtful.” The descriptions quoted above are after Watson softened his comments.

[45]Junk DNA does have a use. It is the portion employed in DNA fingerprinting. Its practicality for this purpose was discovered accidentally by Alec Jeffreys, a scientist at the University of Leicester in England. In 1986 Jeffreys was studying DNA sequences for genetic markers associated with heritable diseases when he was approached by the police and asked if he could help connect a suspect to two murders. He realized his technique ought to work perfectly for solving criminal cases-and so it proved. A young baker with the improbable name of Colin Pitchfork was sentenced to two life terms in prison for the murders.

[46]Though Dutch, Dubois was from Eijsden, a town bordering the French-speaking part of Belgium.

[47]Humans are put in the lamely Homimdae. Its members, traditionally called hominids, include any creatures (including extinct ones) that are more closely related to us than to any surviving chimpanzees. The apes, meanwhile, are lumped together in a family called Pongidae. Many authorities believe that chimps, gorillas, and orangutans should also be included in this family, with humans and chimps in a subfamily called Homininae. The upshot is that the creatures traditionally called hominids become, under this arrangement, hominins. (Leakey and others insist on that designation.) Hominoidea is the name of the aue sunerfamily which includes us.

[48]Absolute brain size does not tell you everything-or possibly sometimes even much. Elephants and whales both have brains larger than ours, but you wouldn’t have much trouble outwitting them in contract negotiations. It is relative size that matters, a point that is often overlooked. As Gould notes, A.africanus had a brain of only 450 cubic centimeters, smaller than that of a gorilla. But a typicalafricanus male weighed less than a hundred pounds, and a female much less still, whereas gorillas can easily top out at 600 pounds (Gould pp. 181-83).

[49]One possibility is that Neandertals and Cro-Magnons had different numbers of chromosomes, a complication that commonly arises when species that are close but not quite identical conjoin. In the equine world, for example, horses have 64 chromosomes and donkeys 62. Mate the two and you get an offspring with a reproductively useless number of chromosomes, 63. You have, in short, a sterile mule.