The Sediments of Time

by Meave Leakey

  There were a few terribly brief intermissions from this deep freeze, and we are enjoying a relatively long one today. The last time there was a peak of warmth similar to global temperatures today was 130,000 years ago near the beginning of an interglacial period that ended 75,000 years ago. Then there was another glacial maxima between 70,000 and 60,000 years ago. This period of lower sea levels and increased aridity coincides with the main exodus of H. sapiens out of Africa all the way to Australia.

  What’s more, the original Europeans—the Neanderthals—evolved in icy Europe at the same time that H. sapiens was evolving in Africa. What is most amazing to me about the Neanderthals is how marvelously cold-adapted they must have been, for they were a very successful species. Compared to the dearth of fossils for other hominin species, they seem to crop up all over the place. The evolution of the Neanderthals began between 300,000 and 250,000 years ago. Like their African cousins, they expanded and contracted multiple times according to the opportunities the shifts in climate offered, and they reached across an area extending from the Iberian Peninsula to southern England and the Mediterranean and across the Caucasus to beyond the Caspian Sea until the Altai Mountains and the Hindu Kush blocked their path farther into Asia. To the north, the arctic blast of ice age winter on the cold steppes presented an equally impenetrable barrier to further dispersal.

  The Neanderthals’ prevalence and their big brains fed the European bias of early palaeontologists who had balked at the idea of an African ancestor. The Neanderthals were the first hominins ever found—the first specimen was discovered in 1829 in Belgium, and the first to be recognised as a Neanderthal was found in a quarry in the Neander Valley in Germany in 1856. So for a long time, there was no other candidate for our immediate ancestor, and no reason to suppose that we didn’t evolve from these human-looking creatures.

  But in common English usage today, calling someone a Neanderthal is usually meant as an insult akin to calling someone primitive and uncivilized. Neanderthals and cavemen are inextricably linked to this day in the popular imagination, with an image of a Hobbesian life that was “nasty, brutish and short,” where hairy, brawny cavemen with huge clubs clobbered one another to death. Evolving from a European Neanderthal may have been viewed as preferable to evolving from an African ape, but it still did not sit at all comfortably with the Christian notion of man being created in the image of God. This bias is seen in the writing of the French palaeontologist Marcellin Boule who, along with Arthur Keith, heavily influenced early thinking on Neanderthals. Boule gives free rein to his prejudices and preconceptions, writing most unscientifically in 1920 of the “rudimentary psychic nature” of Neanderthals, “superior certainly to that of anthropoid apes but markedly inferior to that of any modern race whatsoever,” and the “brutish appearance of this energetic and clumsy body, of the heavy-jawed skull, which itself declares the predominance of functions of a purely vegetative or bestial kind over the functions of the mind.” This compares to his highly poetic praise of modern human contemporaries of Neanderthals “who had a more elegant body, a finer head, an upright and spacious brow, and who have left, in the caves which they inhabited, so much evidence of their manual skill, artistic and religious preoccupations, of their abstract faculties, and who were the first to merit the glorious title of H. sapiens!”

  How Boule arrived at his conclusions of the inferior quality of the Neanderthal mind is only to be supposed at, for the specimen he was comparing to modern humans, a skeleton known informally as the Old Man from La Chapelle-aux-Saints (for his arthritic bones and missing or worn teeth), had an impressive brain capacity of more than 1,600 cc—considerably bigger than the average modern human’s 1,350 cc. He claimed he could tell how rudimentary this brain was from the coarseness of the endocast he moulded from the skull’s interior surface, but his interpretation is totally discredited now. Biases persisted in how people viewed Neanderthals, though, and they inevitably led to a high degree of subjectivity in reconstructions. Reconstructions that imply a brawny dimwit unable to think, let alone survive the rigours of ice age winter, belie the reality that the Neanderthals prospered where no other hominin had done before and prevailed against all odds for well more than a hundred thousand years in the most inclement weather imaginable. The actual evidence points to a far more benign and gentle species that is very closely related to our own and superbly adapted to the unforgiving ice age climate.

  But life was indeed brutish and quite short—very few Neanderthals (less than 10 percent) lived beyond age thirty-five, and most of them died in their late twenties or early thirties. In modern hunter-gatherer societies and tribal agriculturalists without the benefits of modern medicine, this figure is about 50 percent. So few Neanderthals would have reached what in modern terms is considered middle age. That doesn’t leave much time for handing down hard-won knowledge and experience about surviving—or for grandmothering, for that matter. Neanderthals lived a tough life, and this is dramatically demonstrated by the frequent occurrence of lesions on their skeletons. Some of these were the result of quite violent injuries, as evidenced by broken bones. Others are simply the result of malnutrition and disease during crucial periods of growth. But where this picture departs from the brutish caveman savage is that many Neanderthals survived these hardships because the trauma to their bodies healed during life. Rather than clubbing one another to death, they were nursing one another back to health. Neanderthals, like H. erectus before them, were hugely social creatures with bonds that extended well beyond that of mother and child. Society had evolved considerably from H. erectus’s time to include burials, care for the infirm, and very sophisticated toolmaking.

  With all this evidence of intelligence, speculating on the differences in brain function between ourselves and Neanderthals is unenlightened. Our bodies were shaped quite differently, however, and the reasons are mostly due to climate. There are two rules, which are named for their inventors, that pertain to how the shape of animal bodies adapts to climate: Bergmann’s rule, which postulates that in colder conditions body weight will tend to be larger, and Allen’s rule, which states that in colder conditions body extremities will be relatively shorter. For example, the Inuit tend to have thick torsos on squat bodies with short arms, stocky legs, and shorter fingers and toes. Desert-dwelling nomads are on the other end of the spectrum. When Alan Walker was studying the Nariokotome Boy’s skeleton, he looked at the body proportions with Chris Ruff, an expert on body shape and its relationship to ambient temperatures. They found that the Nariokotome Boy’s long slender frame was ideally suited to living in a tropical climate where temperatures hovered around 30°C (86°F) and that his body shape very closely resembled that of modern nomadic Turkana tribesmen.

  Neanderthals had very short, stout bodies and differ most markedly from the tall slender form of desert-dwelling nomads like the Turkana and Masai. Most impressive are the strong, sturdy, heavy bones that allowed for the attachment of massive muscles. In the icehouse climate, persistence hunting was probably much less effective than in the tropics, and running an animal to hypothermic exhaustion was not likely to be a successful hunting strategy. Indeed, we see evidence that Neanderthals fashioned and used fire-hardened and weighted throwing spears. To kill their prey, they would have had to get close to them, which probably accounts for most of the bone injuries they suffered as well as their need for superhuman strength. No modern athlete comes close to the phenomenal power of their bodies, which were built to withstand long periods of heavy physical activity in fiercely cold weather. Chris Ruff and Alan Walker plugged in the Neanderthal body proportions to their temperature model when they were studying the Nariokotome Boy. They found the mean annual temperature for the Neanderthals’ Europe to be -1°C (30°F)—on par with temperatures found above the Arctic Circle today.

  The skulls of Neanderthals are also unmistakable. Like H. erectus, they have a long, low, flattened braincase, but the handlebar brow ridges of solid bone had evolved into two thick prominent arc
hes that are hollow to enclose the frontal sinus. Even more distinctive is the large nasal opening—it looks like somebody got hold of the Neanderthal nose and pulled hard, giving it a pronounced elongated and forward-jutting shape quite different from ours (a sapiens nose is both smaller and tucked in below the brows).

  Neanderthal skulls are unmistakable with their long, low, flattened braincase, thick prominent brow ridges, and large nasal opening: A) Profile comparison of Homo neanderthalensis (left) and Homo sapiens (right) B) Frontal view of Homo neanderthalensis C) Reconstruction of Homo neanderthalensis

  Physical differences notwithstanding, just how different are we from the Neanderthals? Should they be banished from the exulted company of modern humans or admitted to our privileged circle as an immediate family member? This has long been a matter of fierce contention, and the battleground has shifted from bone morphology to include genetic analysis. Both sides agree on at least one thing: Neanderthals and modern humans both evolved in ways that responded to climate: H. sapiens to suit the arid, dry tropics of Africa, and the Neanderthals to survive the glacial and wildly fluctuating conditions of Europe. But the two schools of thought reach widely different conclusions.

  The first group (“splitters”) holds that we evolved in Africa through archaic H. sapiens (sometimes called H. rhodesiensis) and that the Neanderthals evolved in Europe from a different population of archaic H. sapiens (H. heidelbergensis) that had already moved out of Africa. Our separate paths continued as an example of parallel evolution until a full-fledged modern H. sapiens moved out of Africa into Europe some 60,000 years ago. The Neanderthals were a distinct species, and as we have seen, they had impressive qualities in their own right. But as a separate species, they either could not interbreed with H. sapiens—or did so relatively rarely. Thus, when H. sapiens eventually invaded their territory, they were rapidly replaced and quickly thereafter became extinct. Quite simply, we outcompeted the Neanderthals, and the most likely explanation is because we had evolved unique cognitive talents so the Neanderthals’ cold-adapted bodies no longer had the advantage over our puny desert-toned ones—and we outsmarted them. This view is known as the “out of Africa” or “single origin” hypothesis.

  The second school (“lumpers”) believes that there was a lot more gene mixing through interbreeding between the populations. A lead proponent of this alternative theory, the “multiregional hypothesis,” is a man named Erik Trinkaus. In his view, H. erectus evolved into archaic H. sapiens simultaneously in Africa, Asia, and Europe. In Africa and Asia, this intermediate creature evolved into modern H. sapiens while in Europe it evolved into the Neanderthals. A good deal of breeding ensured that the non-African archaic sapiens, and later the Neanderthals, regularly inserted their genes into the evolving African human pool. Eventually, H. sapiens also emerged in Europe and busily bred with the Neanderthals and Asian sapiens to produce the modern homogeneity of our single species. In this scenario, all the larger-brained hominins of the Late Pleistocene were part of a single evolving species—one widely dispersed, interbreeding population that stretched from Africa through Europe to the Far East with some regional and temporal variation. How they managed to traverse the mountains and miles of frozen terrain at such frequent intervals as to keep up a respectable gene flow is anyone’s guess, but the lumpers do not regard the frigid climate as an impediment to their model.

  The fossils, rather unhelpfully, can provide cannon fodder for both theories depending on interpretation. For splitters, the features of the Neanderthals are so distinctive as to clearly represent a well-established species that would not have easily been able to interbreed and produce fertile offspring. This is emphasized by the very distinctive characters evident even in very young children. Usually, a baby is a baby is a baby—features that are evident later in life are not yet distinguishable among the infants of closely related species. But baby Neanderthals do show classic Neanderthal features and a different growth trajectory that is visible from birth. These are clearly manifest on a nine-month-old Neanderthal baby from Amud Cave in Israel and a child from El Sidrón in Spain.

  Tool technology at this time rather supports the splitters. After little to no change in the widespread Acheulean industry used by H. erectus and its descendants in both Africa and Europe for well more than 1.5 million years, a revolutionary breakthrough in production techniques took place in Africa around 300,000 years ago. In contrast to the production of artefacts that rely on visual feedback to guide the maker, the new techniques included a much surer method called “prepared core.” Named after Levallois, the suburb in Paris where the technique was first documented, the Levallois technique entails first preparing the flint nodule with one domed surface. Next, a striking platform is prepared so a flake can be struck off to form a ready-made tool. The process is repeated until the core is too small to remove further flakes. This “prepared core” technique therefore relied on a strong mental template, forethought, and an ability for complex abstract thinking.

  The subsequent appearance of blades, points, microliths, and bone tools as well as evidence of long-distance trade and the use of pigments and ochre appear progressively in Africa over time and at sites widely separated geographically. In Europe, Neanderthals also made stone tools with the Levallois technique, and the Neanderthal and early sapiens toolkits are virtually the same. However, most of the innovations that appear in the African archaeological record of the last 100,000 years never occurred among Neanderthals and do not appear in Eurasia until tens of thousands of years later when H. sapiens replaced the Neanderthals. If the lumpers are correct about the repeated intermixing of the two populations, the archaeological record in Africa should match the archaeological record outside Africa much more closely, and we should not see the delay of tens of thousands of years before the sudden appearance of these modern technologies in Europe.

  Splitters and lumpers alike must explain the fact that the earlier Neanderthals who first appeared in Europe between 130,000 and about 70,000 years ago are much more variable than the many examples from the Neanderthal’s heyday between 50,000 and 40,000 years ago. Splitters do not see this as evidence that interbreeding progressively reduced differences over time as the lumpers do. Instead, the splitters suggest that the earliest Neanderthals in Europe frequently became isolated in remote areas because of the vagaries in climate. These refuge populations each developed slight differences in features through their own small evolutionary experiments, which would explain the large degree of variation much as we have hypothesised for H. erectus. Over time, the Neanderthal recipe for a successful adaptation to the European ice age conditions evolved, and it was representatives of these improved genes that survived and moved into previously isolated areas, mingling with the refuge populations and smoothing the entire gene pool.

  The lumpers, on the other hand, see mixed features in several Neanderthal specimens that they interpret as the result of repeated interbreeding. One such specimen is a child from Lagar Velho in Portugal that has been dated at 24,000 years—after the last of the Neanderthals disappeared around 40,000 years ago. This skeleton is perceived by the discoverers as a Neanderthal-human hybrid, and the presence of some classic Neanderthal features—notably in its body proportions—is interpreted to suggest that there had been interbreeding between Neanderthals and true modern humans for a long period of time. Additional evidence that is advanced to support the lumper interpretation comes from eastern Romania where a mandible and a skull were recently excavated from Pes¸ tera cu Oase (“the cave with bones”) and dated between 37,000 and 42,000 years ago, which is also the earliest fossil record of modern H. sapiens in Europe. These specimens have been interpreted as displaying mixed H. sapiens– Neanderthal characters.

  Scientists are beginning to agree that the splitter view is correct by and large, although most now acknowledge that some interbreeding also occurred. There probably is an inner Neanderthal within us—but whether this is just a dim and distant ghost or an intrinsic and big part of
who we are depends on the degree to which this intermixing happened. For my part, though I find it fascinating, I defer this argument to the experts as it is so removed from my own field of expertise. But this is now the intense focus of new research and debate. It is genetic studies that are slowly bringing convergence between the two opposing views in a way that fossils cannot hope to. Through genetics, we can trace our ancestors’ path out of Africa and across the globe, and we can peer into the chapter of our history that we shared with the Neanderthals to try to figure out what really went on in the sex lives of our ancestors.

  19

  Migrating Mutants

  Every human alive today—more than seven and a half billion people—shares ancestry from a group of about ten thousand African people. That’s all, and it seems simply impossible. What could have possibly happened to reduce our number to such a rare breed? For every living human today to originate from this ancestral population, one of two things had to have happened: either this was the only remnant population of Homo sapiens left alive or this population was isolated—what in genetics is called “structured’—for long enough that we developed separate, private mutations that differentiated this group from all the others. In other words, even if Africa had other populations of early people, they didn’t have any sex with the ten thousand we descend from.