A Short History of Nearly Everything

by Bill Bryson

  The answer, provided by carbon dating, was that the bones' owner had lived there when Lake Mungo was a much more agreeable habitat, a dozen miles long, full of water and fish, fringed by pleasant groves of casuarina trees. To everyone's astonishment, the bones turned out to be 23,000 years old. Other bones found nearby were dated to as much as 60,000 years. This was unexpected to the point of seeming practically impossible. At no time since hominids first arose on Earth has Australia not been an island. Any human beings who arrived there must have come by sea, in large enough numbers to start a breeding population, after crossing sixty miles or more of open water without having any way of knowing that a convenient landfall awaited them. Having landed, the Mungo people had then found their way more than two thousand miles inland from Australia's north coast--the presumed point of entry--which suggests, according to a report in the Proceedings of the National Academy of Sciences, "that people may have first arrived substantially earlier than 60,000 years ago."

  How they got there and why they came are questions that can't be answered. According to most anthropology texts, there's no evidence that people could even speak 60,000 years ago, much less engage in the sorts of cooperative efforts necessary to build ocean-worthy craft and colonize island continents.

  "There's just a whole lot we don't know about the movements of people before recorded history," Alan Thorne told me when I met him in Canberra. "Do you know that when nineteenth-century anthropologists first got to Papua New Guinea, they found people in the highlands of the interior, in some of the most inaccessible terrain on earth, growing sweet potatoes. Sweet potatoes are native to South America. So how did they get to Papua New Guinea? We don't know. Don't have the faintest idea. But what is certain is that people have been moving around with considerable assuredness for longer than traditionally thought, and almost certainly sharing genes as well as information."

  The problem, as ever, is the fossil record. "Very few parts of the world are even vaguely amenable to the long-term preservation of human remains," says Thorne, a sharp-eyed man with a white goatee and an intent but friendly manner. "If it weren't for a few productive areas like Hadar and Olduvai in east Africa we'd know frighteningly little. And when you look elsewhere, often we do know frighteningly little. The whole of India has yielded just one ancient human fossil, from about 300,000 years ago. Between Iraq and Vietnam--that's a distance of some 5,000 kilometers--there have been just two: the one in India and a Neandertal in Uzbekistan." He grinned. "That's not a whole hell of a lot to work with. You're left with the position that you've got a few productive areas for human fossils, like the Great Rift Valley in Africa and Mungo here in Australia, and very little in between. It's not surprising that paleontologists have trouble connecting the dots."

  The traditional theory to explain human movements--and the one still accepted by the majority of people in the field--is that humans dispersed across Eurasia in two waves. The first wave consisted of Homo erectus, who left Africa remarkably quickly--almost as soon as they emerged as a species--beginning nearly two million years ago. Over time, as they settled in different regions, these early erects further evolved into distinctive types--into Java Man and Peking Man in Asia, and Homo heidelbergensis and finally Homo neanderthalensis in Europe.

  Then, something over a hundred thousand years ago, a smarter, lither species of creature--the ancestors of every one of us alive today--arose on the African plains and began radiating outward in a second wave. Wherever they went, according to this theory, these new Homo sapiens displaced their duller, less adept predecessors. Quite how they did this has always been a matter of disputation. No signs of slaughter have ever been found, so most authorities believe the newer hominids simply outcompeted the older ones, though other factors may also have contributed. "Perhaps we gave them smallpox," suggests Tattersall. "There's no real way of telling. The one certainty is that we are here now and they aren't."

  These first modern humans are surprisingly shadowy. We know less about ourselves, curiously enough, than about almost any other line of hominids. It is odd indeed, as Tattersall notes, "that the most recent major event in human evolution--the emergence of our own species--is perhaps the most obscure of all." Nobody can even quite agree where truly modern humans first appear in the fossil record. Many books place their debut at about 120,000 years ago in the form of remains found at the Klasies River Mouth in South Africa, but not everyone accepts that these were fully modern people. Tattersall and Schwartz maintain that "whether any or all of them actually represent our species still awaits definitive clarification."

  The first undisputed appearance of Homo sapiens is in the eastern Mediterranean, around modern-day Israel, where they begin to show up about 100,000 years ago--but even there they are described (by Trinkaus and Shipman) as "odd, difficult-to-classify and poorly known." Neandertals were already well established in the region and had a type of tool kit known as Mousterian, which the modern humans evidently found worthy enough to borrow. No Neandertal remains have ever been found in north Africa, but their tool kits turn up all over the place. Somebody must have taken them there: modern humans are the only candidate. It is also known that Neandertals and modern humans coexisted in some fashion for tens of thousands of years in the Middle East. "We don't know if they time-shared the same space or actually lived side by side," Tattersall says, but the moderns continued happily to use Neandertal tools--hardly convincing evidence of overwhelming superiority. No less curiously, Acheulean tools are found in the Middle East well over a million years ago, but scarcely exist in Europe until just 300,000 years ago. Again, why people who had the technology didn't take the tools with them is a mystery.

  For a long time, it was believed that the Cro-Magnons, as modern humans in Europe became known, drove the Neandertals before them as they advanced across the continent, eventually forcing them to its western margins, where essentially they had no choice but to fall in the sea or go extinct. In fact, it is now known that Cro-Magnons were in the far west of Europe at about the same time they were also coming in from the east. "Europe was a pretty empty place in those days," Tattersall says. "They may not have encountered each other all that often, even with all their comings and goings." One curiosity of the Cro-Magnons' arrival is that it came at a time known to paleoclimatology as the Boutellier interval, when Europe was plunging from a period of relative mildness into yet another long spell of punishing cold. Whatever it was that drew them to Europe, it wasn't the glorious weather.

  In any case, the idea that Neandertals crumpled in the face of competition from newly arrived Cro-Magnons strains against the evidence at least a little. Neandertals were nothing if not tough. For tens of thousands of years they lived through conditions that no modern human outside a few polar scientists and explorers has experienced. During the worst of the ice ages, blizzards with hurricane-force winds were common. Temperatures routinely fell to 50 degrees below zero Fahrenheit. Polar bears padded across the snowy vales of southern England. Neandertals naturally retreated from the worst of it, but even so they will have experienced weather that was at least as bad as a modern Siberian winter. They suffered, to be sure--a Neandertal who lived much past thirty was lucky indeed--but as a species they were magnificently resilient and practically indestructible. They survived for at least a hundred thousand years, and perhaps twice that, over an area stretching from Gibraltar to Uzbekistan, which is a pretty successful run for any species of being.

  Quite who they were and what they were like remain matters of disagreement and uncertainty. Right up until the middle of the twentieth century the accepted anthropological view of the Neandertal was that he was dim, stooped, shuffling, and simian--the quintessential caveman. It was only a painful accident that prodded scientists to reconsider this view. In 1947, while doing fieldwork in the Sahara, a Franco-Algerian paleontologist named Camille Arambourg took refuge from the midday sun under the wing of his light airplane. As he sat there, a tire burst from the heat, and the plane tipped suddenly, str
iking him a painful blow on the upper body. Later in Paris he went for an X-ray of his neck, and noticed that his own vertebrae were aligned exactly like those of the stooped and hulking Neandertal. Either he was physiologically primitive or Neandertal's posture had been misdescribed. In fact, it was the latter. Neandertal vertebrae were not simian at all. It changed utterly how we viewed Neandertals--but only some of the time, it appears.

  It is still commonly held that Neandertals lacked the intelligence or fiber to compete on equal terms with the continent's slender and more cerebrally nimble newcomers, Homo sapiens . Here is a typical comment from a recent book: "Modern humans neutralized this advantage [the Neandertal's considerably heartier physique] with better clothing, better fires and better shelter; meanwhile the Neandertals were stuck with an oversize body that required more food to sustain." In other words, the very factors that had allowed them to survive successfully for a hundred thousand years suddenly became an insuperable handicap.

  Above all the issue that is almost never addressed is that Neandertals had brains that were significantly larger than those of modern people--1.8 liters for Neandertals versus 1.4 for modern people, according to one calculation. This is more than the difference between modern Homo sapiens and late Homo erectus , a species we are happy to regard as barely human. The argument put forward is that although our brains were smaller, they were somehow more efficient. I believe I speak the truth when I observe that nowhere else in human evolution is such an argument made.

  So why then, you may well ask, if the Neandertals were so stout and adaptable and cerebrally well endowed, are they no longer with us? One possible (but much disputed) answer is that perhaps they are. Alan Thorne is one of the leading proponents of an alternative theory, known as the multiregional hypothesis, which holds that human evolution has been continuous--that just as australopithecines evolved into Homo habilis and Homo heidelbergensis became over time Homo neanderthalensis , so modern Homo sapiens simply emerged from more ancient Homo forms. Homo erectus is, on this view, not a separate species but just a transitional phase. Thus modern Chinese are descended from ancient Homo erectus forebears in China, modern Europeans from ancient European Homo erectus , and so on. "Except that for me there are no Homo erectus ," says Thorne. "I think it's a term which has outlived its usefulness. For me, Homo erectus is simply an earlier part of us. I believe only one species of humans has ever left Africa, and that species is Homo sapiens ."

  Opponents of the multiregional theory reject it, in the first instance, on the grounds that it requires an improbable amount of parallel evolution by hominids throughout the Old World--in Africa, China, Europe, the most distant islands of Indonesia, wherever they appeared. Some also believe that multiregionalism encourages a racist view that anthropology took a very long time to rid itself of. In the early 1960s, a famous anthropologist named Carleton Coon of the University of Pennsylvania suggested that some modern races have different sources of origin, implying that some of us come from more superior stock than others. This hearkened back uncomfortably to earlier beliefs that some modern races such as the African "Bushmen" (properly the Kalahari San) and Australian Aborigines were more primitive than others.

  Whatever Coon may personally have felt, the implication for many people was that some races are inherently more advanced, and that some humans could essentially constitute different species. The view, so instinctively offensive now, was widely popularized in many respectable places until fairly recent times. I have before me a popular book published by Time-Life Publications in 1961 called The Epic of Man based on a series of articles in Life magazine. In it you can find such comments as "Rhodesian man ... lived as recently as 25,000 years ago and may have been an ancestor of the African Negroes. His brain size was close to that of Homo sapiens ." In other words black Africans were recently descended from creatures that were only "close" to Homo sapiens .

  Thorne emphatically (and I believe sincerely) dismisses the idea that his theory is in any measure racist and accounts for the uniformity of human evolution by suggesting that there was a lot of movement back and forth between cultures and regions. "There's no reason to suppose that people only went in one direction," he says. "People were moving all over the place, and where they met they almost certainly shared genetic material through interbreeding. New arrivals didn't replace the indigenous populations, they joined them. They became them." He likens the situation to when explorers like Cook or Magellan encountered remote peoples for the first time. "They weren't meetings of different species, but of the same species with some physical differences."

  What you actually see in the fossil record, Thorne insists, is a smooth, continuous transition. "There's a famous skull from Petralona in Greece, dating from about 300,000 years ago, that has been a matter of contention among traditionalists because it seems in some ways Homo erectus but in other ways Homo sapiens . Well, what we say is that this is just what you would expect to find in species that were evolving rather than being displaced."

  One thing that would help to resolve matters would be evidence of interbreeding, but that is not at all easy to prove, or disprove, from fossils. In 1999, archeologists in Portugal found the skeleton of a child about four years old that died 24,500 years ago. The skeleton was modern overall, but with certain archaic, possibly Neandertal, characteristics: unusually sturdy leg bones, teeth bearing a distinctive "shoveling" pattern, and (though not everyone agrees on it) an indentation at the back of the skull called a suprainiac fossa, a feature exclusive to Neandertals. Erik Trinkaus of Washington University in St. Louis, the leading authority on Neandertals, announced the child to be a hybrid: proof that modern humans and Neandertals interbred. Others, however, were troubled that the Neandertal and modern features weren't more blended. As one critic put it: "If you look at a mule, you don't have the front end looking like a donkey and the back end looking like a horse."

  Ian Tattersall declared it to be nothing more than "a chunky modern child." He accepts that there may well have been some "hanky-panky" between Neandertals and moderns, but doesn't believe it could have resulted in reproductively successful offspring. * 49 "I don't know of any two organisms from any realm of biology that are that different and still in the same species," he says.

  With the fossil record so unhelpful, scientists have turned increasingly to genetic studies, in particular the part known as mitochondrial DNA. Mitochondrial DNA was only discovered in 1964, but by the 1980s some ingenious souls at the University of California at Berkeley had realized that it has two features that lend it a particular convenience as a kind of molecular clock: it is passed on only through the female line, so it doesn't become scrambled with paternal DNA with each new generation, and it mutates about twenty times faster than normal nuclear DNA, making it easier to detect and follow genetic patterns over time. By tracking the rates of mutation they could work out the genetic history and relationships of whole groups of people.

  In 1987, the Berkeley team, led by the late Allan Wilson, did an analysis of mitochondrial DNA from 147 individuals and declared that the rise of anatomically modern humans occurred in Africa within the last 140,000 years and that "all present-day humans are descended from that population." It was a serious blow to the multiregionalists. But then people began to look a little more closely at the data. One of the most extraordinary points--almost too extraordinary to credit really--was that the "Africans" used in the study were actually African-Americans, whose genes had obviously been subjected to considerable mediation in the past few hundred years. Doubts also soon emerged about the assumed rates of mutations.

  By 1992, the study was largely discredited. But the techniques of genetic analysis continued to be refined, and in 1997 scientists from the University of Munich managed to extract and analyze some DNA from the arm bone of the original Neandertal man, and this time the evidence stood up. The Munich study found that the Neandertal DNA was unlike any DNA found on Earth now, strongly indicating that there was no genetic connection between Ne
andertals and modern humans. Now this really was a blow to multiregionalism.

  Then in late 2000 Nature and other publications reported on a Swedish study of the mitochondrial DNA of fifty-three people, which suggested that all modern humans emerged from Africa within the past 100,000 years and came from a breeding stock of no more than 10,000 individuals. Soon afterward, Eric Lander, director of the Whitehead Institute/Massachusetts Institute of Technology Center for Genome Research, announced that modern Europeans, and perhaps people farther afield, are descended from "no more than a few hundred Africans who left their homeland as recently as 25,000 years ago."

  As we have noted elsewhere in the book, modern human beings show remarkably little genetic variability--"there's more diversity in one social group of fifty-five chimps than in the entire human population," as one authority has put it--and this would explain why. Because we are recently descended from a small founding population, there hasn't been time enough or people enough to provide a source of great variability. It seemed a pretty severe blow to multiregionalism. "After this," a Penn State academic told the Washington Post , "people won't be too concerned about the multiregional theory, which has very little evidence."

  But all of this overlooked the more or less infinite capacity for surprise offered by the ancient Mungo people of western New South Wales. In early 2001, Thorne and his colleagues at the Australian National University reported that they had recovered DNA from the oldest of the Mungo specimens--now dated at 62,000 years--and that this DNA proved to be "genetically distinct."

  The Mungo Man, according to these findings, was anatomically modern--just like you and me--but carried an extinct genetic lineage. His mitochondrial DNA is no longer found in living humans, as it should be if, like all other modern people, he was descended from people who left Africa in the recent past.