A Short History of Nearly Everything: Special Illustrated Edition

by Bill Bryson

  Eventually the eukaryotes learned an even more singular trick. It took a long time—a billion years or so—but it was a good one when they mastered it. They learned to form together into complex multicellular beings. Thanks to this innovation, big, complicated, visible entities like us were possible. Planet Earth was ready to move on to its next ambitious phase.

  But before we get too excited about that, it is worth remembering that the world, as we are about to see, still belongs to the very small.

  1 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) called Methanosarcina barkeri.

  The AIDS virus, HIV, greatly magnified. The virus can sit, harmless and unnoticed, in the nuclei of cells for years before springing into action. (credit 20.1)

  SMALL WORLD

  It’s probably not a good idea to take too personal an interest in your microbes. Louis Pasteur, the great French chemist and bacteriologist, became so preoccupied with his that he took to peering critically at every dish placed before him with a magnifying glass, a habit that presumably did not win him many repeat invitations to dinner.

  In fact, there is no point in trying to hide from your bacteria, for they are on and around you always, in numbers you can’t conceive of. If you are in good health and averagely diligent about hygiene, you will have a herd of about one trillion bacteria grazing on your fleshy plains—about a hundred thousand of them on every square centimetre of skin. They are there to dine off the ten billion or so flakes of skin you shed every day, plus all the tasty oils and fortifying minerals that seep out from every pore and fissure. You are for them the ultimate buffet, with the convenience of warmth and constant mobility thrown in. By way of thanks, they give you B.O.

  And those are just the bacteria that inhabit your skin. There are trillions more tucked away in your gut and nasal passages, clinging to your hair and eyelashes, swimming over the surface of your eyes, drilling through the enamel of your teeth. Your digestive system alone is host to more than a hundred trillion microbes, of at least four hundred types. Some deal with sugars, some with starches, some attack other bacteria. A surprising number, like the ubiquitous intestinal spirochetes, have no detectable function at all. They just seem to like to be with you. Every human body consists of about ten quadrillion cells, but is host to about a hundred quadrillion bacterial cells. They are, in short, a big part of us. From the bacteria’s point of view, of course, we are a rather small part of them.

  Because we humans are big and clever enough to produce and use antibiotics and disinfectants, it is easy to convince ourselves that we have banished bacteria to the fringes of existence. Don’t you believe it. Bacteria may not build cities or have interesting social lives, but they will be here when the Sun explodes. This is their planet, and we are on it only because they allow us to be.

  Bacteria, never forget, got along for billions of years without us. We couldn’t survive a day without them. They process our wastes and make them usable again; without their diligent munching nothing would rot. They purify our water and keep our soils productive. Bacteria synthesize vitamins in our gut, convert the things we eat into useful sugars and polysaccharides, and go to war on alien microbes that slip down our gullet.

  Human eyelashes magnified two hundred times show a world at skin level that most of us are unaware of—and probably glad not to be. Shafts of hair, coloured green here, emerge from crusty follicles, which are also home to tiny eyelash mites, their tails just visible at each opening. The yellowish patches between the follicles are flakes of dried skin. (credit 20.3)

  We depend totally on bacteria to pluck nitrogen from the air and convert it into useful nucleotides and amino acids for us. It is a prodigious and gratifying feat. As Margulis and Sagan note, to do the same thing industrially (as when making fertilizers) manufacturers must heat the source materials to 500 degrees Celsius and squeeze them to 300 times normal pressures. Bacteria do the same thing all the time without fuss, and thank goodness, for no larger organism could survive without the nitrogen they pass on. Above all, microbes continue to provide us with the air we breathe and to keep the atmosphere stable. Microbes, including the modern versions of cyanobacteria, supply the greater part of the planet’s breathable oxygen. Algae and other tiny organisms bubbling away in the sea blow out about 150 billion kilograms of the stuff every year.

  And they are amazingly prolific. The more frantic among them can yield a new generation in less than ten minutes; Clostridium perfringens, the disagreeable little organism that causes gangrene, can reproduce in nine minutes and then begin at once to split again. At such a rate, a single bacterium could theoretically produce more offspring in two days than there are protons in the universe. “Given an adequate supply of nutrients, a single bacterial cell can generate 280,000 billion individuals in a single day,” according to the Belgian biochemist and Nobel laureate Christian de Duve. In the same period, a human cell can just about manage a single division.

  Clostridium perfringens, one of the most pernicious of bacteria, can lie dormant for long periods, then flood a host with billions of offspring in a matter of hours. The unhappy results range from blood poisoning to gas gangrene. (credit 20.2)

  About once every million divisions, they produce a mutant. Usually this is bad luck for the mutant—for an organism, change is always risky—but just occasionally the new bacterium is endowed with some accidental advantage, such as the ability to elude or shrug off an attack of antibiotics. With this ability to evolve rapidly goes another, even scarier advantage. Bacteria share information. Any bacterium can take pieces of genetic coding from any other. Essentially, as Margulis and Sagan put it, all bacteria swim in a single gene pool. Any adaptive change that occurs in one area of the bacterial universe can spread to any other. It’s rather as if a human could go to an insect to get the necessary genetic coding to sprout wings or walk on ceilings. It means that from a genetic point of view bacteria have become a single superorganism—tiny, dispersed, but invincible.

  They will live and thrive on almost anything you spill, dribble or shake loose. Just give them a little moisture—as when you run a damp cloth over a counter—and they will bloom as if created from nothing. They will eat wood, the glue in wallpaper, the metals in hardened paint. Scientists in Australia found microbes known as Thiobacillus concretivorans which lived in—indeed, could not live without—concentrations of sulphuric acid strong enough to dissolve metal. A species called Micrococcus radiophilus was found living happily in the waste tanks of nuclear reactors, gorging itself on plutonium and whatever else was there. Some bacteria break down chemical materials from which, as far as we can tell, they gain no benefit at all.

  They have been found living in boiling mud pots and lakes of caustic soda, deep inside rocks, at the bottom of the sea, in hidden pools of icy water in the McMurdo Dry Valleys of Antarctica, and 11 kilometres down in the Pacific Ocean where pressures are more than a thousand times greater than at the surface, or equivalent to being squashed beneath fifty jumbo jets. Some of them seem to be practically indestructible. Deinococcus radiodurans is, according to The Economist, “almost immune to radioactivity.” Blast its DNA with radiation and the pieces immediately re-form “like the scuttling limbs of an undead creature from a horror movie.”

  Perhaps the most extraordinary survival yet found was that of a Streptococcus bacterium that was recovered from the sealed lens of a camera that had stood on the Moon for two years. In short, there are few environments in which bacteria aren’t prepared to live. “They are finding now that when they push probes into ocean vents so hot that the probes actually start to melt, there are bacteria even there,” Victoria Bennett told me.

  In the 192
0s two scientists at the University of Chicago, Edson Bastin and Frank Greer, announced that they had isolated from oil wells strains of bacteria that had been living at depths of 600 metres. The notion was dismissed as fundamentally preposterous—there was nothing to live on at 600 metres—and for fifty years it was assumed that their samples had been contaminated with surface microbes. We now know that there are a lot of microbes living deep within the Earth, many of which have nothing at all to do with the conventionally organic world. They eat rocks or, rather, the stuff that’s in rocks—iron, sulphur, manganese and so on. And they breathe odd things too—iron, chromium, cobalt, even uranium. Such processes may be instrumental in concentrating gold, copper and other precious metals, and possibly deposits of oil and natural gas. It has even been suggested that their tireless nibblings created the Earth’s crust.

  Some scientists now think that there could be as much as 100 trillion tonnes of bacteria living beneath our feet in what are known as subsurface lithoautotrophic microbial ecosystems—SLiME for short. Thomas Gold of Cornell University has estimated that if you took all the bacteria out of the Earth’s interior and dumped them on the surface, they would cover the planet to a depth of 15 metres—the height of a four-storey building. If the estimates are correct, there could be more life under the Earth than on top of it.

  At depth, microbes shrink in size and become extremely sluggish. The liveliest of them may divide no more than once a century, some no more than perhaps once in five hundred years. As The Economist has put it: “The key to long life, it seems, is not to do too much.” When things are really tough, bacteria are prepared to shut down all systems and wait for better times. In 1997 scientists successfully activated some anthrax spores that had lain dormant for eighty years in a museum display in Trondheim, Norway. Other micro-organisms have leaped back to life after being released from a 118-year-old can of meat and a 166-year-old bottle of beer. In 1996, scientists at the Russian Academy of Science claimed to have revived bacteria frozen in Siberian permafrost for three million years. But the record claim for durability so far is one made by Russell Vreeland and colleagues at West Chester University in Pennsylvania in 2000, when they announced that they had resuscitated 250-million-year-old bacteria called Bacillus permians that had been trapped in salt deposits 600 metres underground in Carlsbad, New Mexico. If so, this microbe is older than the continents.

  The report met with some understandable dubiousness. Many biochemists maintained that over such a span the microbe’s components would have become uselessly degraded unless the bacterium roused itself from time to time. However, if the bacterium did stir occasionally, there was no plausible internal source of energy that could have lasted so long. The more doubtful scientists suggested that the sample might have been contaminated, if not during its retrieval then perhaps while still buried. In 2001, a team from Tel Aviv University argued that B. permians was almost identical to a strain of modern bacteria, Bacillus marismortui, found in the Dead Sea. Only two of its genetic sequences differed, and then only slightly.

  “Are we to believe,” the Israeli researchers wrote, “that in 250 million years B. permians has accumulated the same amount of genetic differences that could be achieved in just 3–7 days in the laboratory?” In reply, Vreeland suggested that “bacteria evolve faster in the lab than they do in the wild.”

  Maybe.

  It is a remarkable fact that well into the space age, most school textbooks divided the world of the living into just two categories—plant and animal. Micro-organisms hardly featured. Amoebas and similar single-celled organisms were treated as proto-animals and algae as proto-plants. Bacteria were usually lumped in with plants, too, even though everyone knew they didn’t belong there. As far back as the late nineteenth century the German naturalist Ernst Haeckel had suggested that bacteria deserved to be placed in a separate kingdom, which he called Monera, but the idea didn’t begin to catch on among biologists until the 1960s, and then only among some of them. (I note that my trusty American Heritage desk dictionary from 1969 doesn’t recognize the term.)

  A “Family Tree of Man” as conceived by the German naturalist Ernst Haeckel in 1874. Haeckel was the first to place bacteria in a separate kingdom. (credit 20.4)

  Many organisms in the visible world were also poorly served by the traditional division. Fungi, the group that includes mushrooms, moulds, mildews, yeasts and puffballs, were nearly always treated as botanical objects, though in fact almost nothing about them—how they reproduce and respire, how they build themselves—matches anything in the plant world. Structurally, they have more in common with animals in that they build their cells from chitin, a material that gives them their distinctive texture. The same substance is used to make the shells of insects and the claws of mammals, though it isn’t nearly so tasty in a stag beetle as in a Portobello mushroom. Above all, unlike all plants, fungi don’t photosynthesize, so they have no chlorophyll and thus are not green. Instead they grow directly on their food source, which can be almost anything. Fungi will eat the sulphur off a concrete wall or the decaying matter between your toes—two things no plant will do. Almost the only plant-like quality they have is that they root.

  Ernst Haeckel (left) and an unidentified friend display the equipment, attire and insouciant attitude appropriate to a scientific field trip in the mid-nineteenth century. Although he is remembered for his biological classifications, Haeckel’s speciality was sponges and other marine organisms. (credit 20.5)

  Even less comfortably susceptible to categorization was the peculiar group of organisms formally called myxomycetes but more commonly known as slime moulds. The name no doubt has much to do with their obscurity. An appellation that sounded a little more dynamic—“ambulant self-activating protoplasm,” say—and less like the stuff you find when you reach deep into a clogged drain would almost certainly have earned these extraordinary entities a more immediate share of the attention they deserve, for slime moulds are, make no mistake, among the most interesting organisms in nature. When times are good, they exist as one-celled individuals, much like amoebas. But when conditions grow tough, they crawl to a central gathering place and become, almost miraculously, a slug. The slug is not a thing of beauty and it doesn’t go terribly far—usually just from the bottom of a pile of leaf litter to the top, where it is in a slightly more exposed position—but for millions of years this may well have been the niftiest trick in the universe.

  And it doesn’t stop there. Having hauled itself up to a more favourable locale, the slime mould transforms itself yet again, taking on the form of a plant. By some curious orderly process the cells reconfigure, like the members of a tiny marching band, to make a stalk atop of which forms a bulb known as a fruiting body. Inside the fruiting body are millions of spores which, at the appropriate moment, are released to the wind to blow away to become single-celled organisms that can start the process again.

  For years, slime moulds were claimed as protozoa by zoologists and as fungi by mycologists, though most people could see they didn’t really belong anywhere. When genetic testing arrived, people in lab coats were surprised to find that slime moulds were so distinctive and peculiar that they weren’t directly related to anything else in nature, and sometimes not even to each other.

  In 1969, in an attempt to bring some order to the growing inadequacies of classification, an ecologist from Cornell named R. H. Whittaker unveiled in the journal Science a proposal to divide life into five principal branches—kingdoms, as they are known—called Animalia, Plantae, Fungi, Protista and Monera. Protista was a modification of an earlier term, Protoctista, which had been suggested a century earlier by a Scottish biologist named John Hogg, and was meant to describe any organisms that were neither plant nor animal.

  Though Whittaker’s new scheme was a great improvement, Protista remained ill defined. Some taxonomists reserved the term for large unicellular organisms—the eukaryotes—but others treated it as the kind of odd-sock drawer of biology, putting into it anything
that didn’t fit anywhere else. It included (depending on which text you consulted) slime moulds, amoebas, even seaweed, among much else. By one calculation it contained as many as two hundred thousand different species of organism all told. That’s a lot of odd socks.

  Ironically, just as Whittaker’s five-kingdom classification was beginning to find its way into textbooks, an unassuming academic at the University of Illinois was groping his way towards a discovery that would challenge everything. His name was Carl Woese (rhymes with rose) and since the mid-1960s—or about as early as it was possible to do so—he had been quietly studying genetic sequences in bacteria. In the early days, this was an exceedingly painstaking process. Work on a single bacterium could easily consume a year. At that time, according to Woese, only about five hundred species of bacteria were known, which is fewer than the number of species you have in your mouth. Today the number is about ten times that, though that is still far short of the 26,900 species of algae, 70,000 of fungi, and 30,800 of amoebas and related organisms whose biographies fill the annals of biology.

  Carl Woese of the University of Illinois, whose studies of the genes of micro-organisms led him to conclude that the divisions of life at the unicellular level were far more complicated than was generally supposed. (credit 20.6)

  It isn’t simple indifference that keeps the total low. Bacteria can be exasperatingly difficult to isolate and study. Only about 1 per cent will grow in culture. Considering how wildly adaptable they are in nature, it is an odd fact that the one place they seem not to wish to live is a petri dish. Plop them on a bed of agar and pamper them as you will, and most will just lie there, declining every inducement to bloom. Any bacterium that thrives in a lab is by definition exceptional, and yet these were, almost exclusively, the organisms studied by microbiologists. It was, said Woese, “like learning about animals from visiting zoos.”