by Bill Bryson
With so little to be certain about, scientists often have to make assumptions based on other objects found nearby, and these may be little more than valiant guesses. As Alan Walker and Pat Shipman have drily observed, if you correlate tool discovery with the species of creature most often found nearby, you would have to conclude that early hand tools were mostly made by antelopes.
Perhaps nothing better typifies the confusion than the fragmentary bundle of contradictions that was Homo habilis. Simply put, habilis bones make no sense. When arranged in sequence, they show males and females evolving at different rates and in different directions—the males becoming less apelike and more human with time, while females from the same period appear to be moving away from humanness towards greater apeness. Some authorities don’t believe habilis is a valid category at all. Tattersall and his colleague Jeffrey Schwartz dismiss it as a mere “wastebasket species”—one into which unrelated fossils “could be conveniently swept.” Even those who see habilis as an independent species don’t agree on whether it is of the same genus as us or is from a side branch that never came to anything.
Finally, but perhaps above all, human nature is a factor in all this. Scientists have a natural tendency to interpret finds in the way that most flatters their stature. It is a rare palaeontologist indeed who announces that he has found a cache of bones but that they are nothing to get excited about. As John Reader understatedly observes in the book Missing Links, “It is remarkable how often the first interpretations of new evidence have confirmed the preconceptions of its discoverer.”
All this leaves ample room for arguments, of course, and no bunch of people likes to argue more than palaeoanthropologists. “And of all the disciplines in science, paleoanthropology boasts perhaps the largest share of egos,” say the authors of the recent Java Man—a book, it may be noted, that itself devotes long, wonderfully unselfconscious passages to attacks on the inadequacies of others, in particular the authors’ former close colleague Donald Johanson.
So, bearing in mind that there is little you can say about human prehistory that won’t be disputed by someone somewhere, other than that we most certainly had one, what we think we know about who we are and where we come from is roughly this.
For the first 99.99999 per cent of our history as organisms, we were in the same ancestral line as chimpanzees. Virtually nothing is known about the prehistory of chimpanzees, but whatever they were, we were. Then, about seven million years ago, something major happened. A group of new beings emerged from the tropical forests of Africa and began to move about on the open savanna.
These were the australopithecines, and for the next five million years they would be the world’s dominant hominid species. (Austral is from the Latin for “southern” and has no connection in this context with Australia.) Australopithecines came in several varieties, some slender and gracile, like Raymond Dart’s Taung child, others more sturdy and robust, but all were capable of walking upright. Some of these species existed for well over a million years, others for a more modest few hundred thousand, but it is worth bearing in mind that even the least successful had histories many times longer than we have yet achieved.
The most famous hominid remains in the world are those of a 3.18-million-year-old australopithecine found at Hadar in Ethiopia in 1974 by a team led by Donald Johanson. Formally known as A.L. (for “Afar Locality”) 288–1, the skeleton became more familiarly known as Lucy, after the Beatles song “Lucy in the Sky with Diamonds.” Johanson has never doubted her importance. “She is our earliest ancestor, the missing link between ape and human,” he has said.
Lucy was tiny—just three and a half feet tall. She could walk, though how well is a matter of some dispute. She was evidently a good climber too. Much else is unknown. Her skull was almost entirely missing, so little could be said with confidence about her brain size, though skull fragments suggested it was small. Most books describe Lucy’s skeleton as being 40 per cent complete, though some put it closer to half and one produced by the American Museum of Natural History describes Lucy as two-thirds complete. The BBC television series Ape Man actually called it “a complete skeleton,” even while showing that it was anything but.
The American Donald Johanson shown with the (mostly reconstructed) skull of Lucy, the most famous of early hominids, which he discovered in Ethiopia in 1974. (Credit 28.7)
A human body has 206 bones, but many of these are repeated. If you have the left femur from a specimen, you don’t need the right to know its dimensions. Strip out all the redundant bones and the total you are left with is 120—what is called a half skeleton. Even by this fairly accommodating standard, and even counting the slightest fragment as a full bone, Lucy constituted only 28 per cent of a half skeleton (and only about 20 per cent of a full one).
About a fifth of Lucy’s bones were found with the skull fragments. (Credit 28.7a)
In The Wisdom of the Bones, Alan Walker recounts how he once asked Johanson how he had come up with a figure of 40 per cent. Johanson breezily replied that he had discounted the 106 bones of the hands and feet—more than half the body’s total, and a fairly important half, too, one would have thought, since Lucy’s principal defining attribute was the use of those hands and feet to deal with a changing world. At all events, rather less is known about Lucy than is generally supposed. It isn’t even actually known that she was a female. Her sex is merely presumed from her diminutive size.
Two years after Lucy’s discovery, at Laetoli in Tanzania Mary Leakey found footprints left by two individuals from—it is thought—the same family of hominids. The prints had been made when two australopithecines had walked through muddy ash following a volcanic eruption. The ash had later hardened, preserving the impressions of their feet for a distance of over 23 metres.
Model of Lucy done by the artist John Gurche. Lucy was slightly over three feet tall and had a brain the size of an orange, but how she moved and lived are matters of dispute. She came from a group known as australopithecines. (Credit 28.8)
The American Museum of Natural History in New York has an absorbing diorama that records the moment of their passing. It depicts life-sized recreations of a male and a female walking side by side across the ancient African plain. They are hairy and chimp-like in dimensions, but have a bearing and gait that suggest humanness. The most striking feature of the display is that the male holds his left arm protectively around the female’s shoulder. It is a tender and affecting gesture, suggestive of close bonding.
The actual footprints, found in Tanzania by Mary Leakey in 1977. (Credit 28.9)
The tableau is presented with such conviction that it is easy to overlook the consideration that virtually everything above the footprints is imaginary Almost every external aspect of the two figures—degree of hairiness, facial appendages (whether they had human noses or chimp noses), expressions, skin colour, size and shape of the female’s breasts—is necessarily suppositional. We can’t even say that they were a couple. The female figure may in fact have been a child. Nor can we be certain that they were australopithecines. They are assumed to be australopithecines because there are no other known candidates.
I had been told that they were posed like that because during the building of the diorama the female figure kept toppling over, but Ian Tattersall insists with a laugh that the story is untrue. “Obviously we don’t know whether the male had his arm around the female or not, but we do know from the stride measurements that they were walking side by side and close together—close enough to be touching. It was quite an exposed area, so they were probably feeling vulnerable. That’s why we tried to give them slightly worried expressions.”
The American Museum of Natural History’s life-size diorama of two australopithecines, displaced by a volcanic eruption, nervously making their way across open ground where they are vulnerable to attack, leaving footprints in the fresh ash as they go. (Credit 28.10)
I asked him if he was troubled about the amount of licence that was taken in recons
tructing the figures. “It’s always a problem in making recreations,” he agreed readily enough. “You wouldn’t believe how much discussion can go into deciding details like whether Neandertals had eyebrows or not. It was just the same for the Laetoli figures. We simply can’t know the details of what they looked like, but we can convey their size and posture and make some reasonable assumptions about their probable appearance. If I had it to do again, I think I might have made them just slightly more apelike and less human. These creatures weren’t humans. They were bipedal apes.”
Until very recently it was assumed that we were descended from Lucy and the Laetoli creatures, but now many authorities aren’t so sure. Although certain physical features (the teeth, for instance) suggest a possible link between us, other parts of the australopithecine anatomy are more troubling. In their book Extinct Humans, Tattersall and Schwartz point out that the upper portion of the human femur is very like that of the apes but not like that of the australopithecines; so if Lucy is in a direct line between apes and modern humans, it means we must have adopted an australopithecine femur for a million years or so, then gone back to an ape femur when we moved on to the next phase of our development. They believe, in fact, that not only was Lucy not our ancestor, she wasn’t even much of a walker.
“Lucy and her kind did not locomote in anything like the modern human fashion,” insists Tattersall. “Only when these hominids had to travel between arboreal habitats would they find themselves walking bipedally, ‘forced’ to do so by their own anatomies.” Johanson doesn’t accept this. “Lucy’s hips and the muscular arrangement of her pelvis,” he has written, “would have made it as hard for her to climb trees as it is for modern humans.”
Matters grew murkier still in 2001 and 2002 when four exceptional new specimens were found. One, discovered by Maeve Leakey of the famous fossil-hunting family at Lake Turkana in Kenya and called Kenyanthropus platyops (“Kenyan flat-face”), is from about the same time as Lucy and raises the possibility that it was our ancestor and Lucy merely an unsuccessful side branch. Also found in 2001 were Ardipithecus ramidus kadabba, dated at between 5.2 million and 5.8 million years old, and Orrorin tugenensis, thought to be six million years old, making it the oldest hominid yet found—but only for a brief while. In the summer of 2002 a French team working in the Djurab Desert of Chad (an area that had never before yielded ancient bones) found a hominid almost seven million years old, which they labelled Sahelanthropus tchadensis. (Some critics believe that it was not human but an early ape, and therefore should be called Sahelpithecus.) All these were early creatures and quite primitive, but they walked upright, and they were doing it far earlier than previously thought.
A young Maeve Leakey uncovers a specimen in Kenya. In 2001, at Lake Turkana, Leakey discovered an early hominid, Kenyanthropus platyops (“Kenyan flat-face”), which could be a direct ancestor of modern humans. (Credit 28.11)
Bipedalism is a demanding and risky strategy. It means refashioning the pelvis into a full load-bearing instrument. To preserve the required strength, the birth canal in the female must be comparatively narrow. This has two very significant immediate consequences and one longer-term one. First, it means a lot of pain for any birthing mother and a greatly increased danger of fatality to mother and baby both. Moreover, to get the baby’s head through such a tight space it must be born while its brain is still small—and while the baby, therefore, is still helpless. This means long-term infant care, which in turn implies solid male-female bonding.
Working out the line of human evolution, which has never been easy, lurched into confusing new territory in the early twenty-first century with the discovery of several new hominids, among them Kenyanthropus platyops (shown here), Orrorin tugenensis and Ardipithecus ramidus kadabba, all of which walked upright and may be directly ancestral to us. (Credit 28.12)
All this is problematic enough when you are the intellectual master of the planet, but when you are a small, vulnerable australopithecine, with a brain about the size of an orange,3 the risk must have been enormous.
The Masai Mara National Reserve in Kenya. The shrinking of jungles and spread of savanna as a result of climate change compelled hominids to adapt or die. (Credit 28.13)
So why did Lucy and her kind come down from the trees and out of the forests? Probably they had no choice. The slow rise of the Isthmus of Panama had cut the flow of waters from the Pacific into the Atlantic, diverting warming currents away from the Arctic and leading to the onset of an exceedingly sharp ice age in northern latitudes. In Africa, this would have produced seasonal drying and cooling, gradually turning jungle into savanna. “It was not so much that Lucy and her like left the forests,” John Gribbin has written, “but that the forests left them.”
But stepping out onto the open savanna also clearly left the early hominids much more exposed. An upright hominid could see better, but could also be seen better. Even now, as a species we are almost preposterously vulnerable in the wild. Nearly every large animal you care to name is stronger, faster and toothier than us. Faced with attack, modern humans have only two advantages. We have a good brain, with which we can devise strategies; and we have hands, with which we can fling or brandish hurtful objects. We are the only creature that can harm at a distance. We can thus afford to be physically vulnerable.
All the elements would appear to have been in place for the rapid evolution of a potent brain, and yet that seems not to have happened. For over three million years, Lucy and her fellow australopithecines scarcely changed at all. Their brain didn’t grow and there is no sign that they used even the simplest tools. What is stranger still is that we now know that for about a million years they lived alongside other early hominids who did use tools, yet the australopithecines never took advantage of this useful technology that was all around them.
At one point between three million and two million years ago, it appears there may have been as many as six hominid types co-existing in Africa. Only one, however, was fated to last: Homo, which emerged from the mists beginning about two million years ago. No-one knows quite what the relationship was between australopithecines and Homo, but what is known is that they co-existed for something over a million years before all the australopithecines, robust and gracile alike, vanished mysteriously, and possibly abruptly, over a million years ago. No-one knows why they disappeared. “Perhaps,” suggests Matt Ridley, “we ate them.”
Two of the millions of hand-axes found in the Olduvai Gorge in Tanzania. Such axes were made by Homo erectus, the first tool-making creature. (Credit 28.14)
Conventionally, the Homo line begins with Homo habilis, a creature about whom we know almost nothing, and concludes with us, Homo sapiens (literally “man the thinker”). In between, and depending on which opinions you value, there have been half a dozen other Homo species: Homo ergaster, Homo neanderthalensis, Homo rudolfensis, Homo heidelbergensis, Homo erectus and Homo antecessor.
Homo habilis (“handy man”) was named by Louis Leakey and colleagues in 1964 and was so called because it was the first hominid to use tools, albeit very simple ones. It was a fairly primitive creature, much more chimpanzee than human, but its brain was about 50 per cent larger than that of Lucy in gross terms and not much less large proportionally, so it was the Einstein of its day. No persuasive reason has ever been adduced for why hominid brains suddenly began to grow two million years ago. For a long time it was assumed that big brains and upright walking were directly related—that the movement out of the forests necessitated cunning new strategies that fed off or promoted braininess—so it was something of a surprise, after the repeated discoveries of so many bipedal dullards, to realize that there was no apparent connection between them at all.
“There is simply no compelling reason we know of to explain why human brains got large,” says Tattersall. Huge brains are demanding organs: they make up only 2 per cent of the body’s mass, but devour 20 per cent of its energy. They are also comparatively picky in what they use as fuel. If you never
ate another morsel of fat, your brain would not complain because it won’t touch the stuff. It wants glucose instead, and lots of it, even if it means short-changing other organs. As Guy Brown notes: “The body is in constant danger of being depleted by a greedy brain, but cannot afford to let the brain go hungry as that would rapidly lead to death.” A big brain needs more food and more food means increased risk.
Richard Leakey, of the famous clan of African palaeoanthropologists, shown on the cover of Time magazine in 1977 with a model of Homo habilis, a species discovered by his father, Louis, in 1964. (Credit 28.15)
Tattersall thinks the rise of a big brain may simply have been an evolutionary accident. He believes with Stephen Jay Gould that if you replayed the tape of life—even if you ran it back only a relatively short way to the dawn of hominids—the chances are “quite unlikely” that modern humans or anything like them would be here now.
“One of the hardest ideas for humans to accept,” he says, “is that we are not the culmination of anything. There is nothing inevitable about our being here. It is part of our vanity as humans that we tend to think of evolution as a process that, in effect, was programmed to produce us. Even anthropologists tended to think this way right up until the 1970s.” Indeed, as recently as 1991, in the popular textbook The Stages of Evolution, C. Loring Brace stuck doggedly to the linear concept, acknowledging just one evolutionary dead end, the robust australopithecines. Everything else represented a straightforward progression—each species of hominid carrying the baton of development so far, then handing it on to a younger, fresher runner. Now, however, it seems certain that many of these early forms followed side trails that didn’t come to anything.