Lone Survivors (12 page)

As we saw, teeth are a valuable resource in studies of our evolution, and because they are already highly mineralized, they preserve very well as fossils. Their size and shape are largely under genetic control (identical twins have similar teeth), and the form of the tooth crown has proved particularly useful in comparing fossil and recent humans. Distinctive patterns of tooth cusps and wrinkles characterize different populations today; a set of unworn teeth can be assigned to a region of the world with a fair degree of confidence using forensics. The anthropologist Christy Turner used this variation to propose an “Out of Asia” scenario for recent human evolution twenty years ago, based on the fact that the “average” dental morphology today can be found in the aboriginal peoples of southeast Asia. He argued that these populations were closest to the original modern human dental pattern, and that this indicated the location of the original source area for
H. sapiens
.

However, Christy's approach could not account for the undoubted similarity between recent Australian and African dental patterns, and I, together with my colleagues Tim Compton and Louise Humphrey, added fossil teeth from Europe to the mix, showing that an African origin for our present dental variation was still the most likely. That conclusion has been further strengthened by Christy's former students Joel Irish and Shara Bailey, who have added many other fossil teeth to their analyses. This kind of work has also been important in studies of earlier human evolution, for example, in showing that the Atapuerca Sima de los Huesos fossils are clearly related to later Neanderthals, and that the Skhul and Qafzeh early moderns from Israel have “African” traits in their teeth.

The famous British archaeological site of Boxgrove, near Chichester, has produced over four hundred beautifully made flint handaxes from levels also rich with the remains of interglacial mammals such as horse, red deer, elephant, and rhino. The fact that even the rhino bones showed extensive evidence of butchery led to a reevaluation of the capabilities of hunter-gatherers 500,000 years ago, in terms of their primary access to such resources. These people were not merely scavenging; they were apparently also highly capable hunters. They could secure the carcasses of large mammals for the extraction of the maximum nutritional benefit in a landscape populated by dangerous competitors such as lions, wolves, and large hyenas.

Most of the four hundred handaxes from Boxgrove, with the British Museum curator Claire Fisher.

The importance of Boxgrove was heightened by the 1993 discovery of a human shinbone attributed to
Homo heidelbergensis
, and two years later, two lower incisor teeth from another individual were discovered. Work with conventional light microscopes and scanning electron microscopes revealed a great deal of the evidence of animal bone butchery and showed that the Boxgrove tibia had been gnawed at one end by a medium-sized carnivore such as a wolf or a hyena. Microscopic studies also showed that the front surfaces of the incisors were covered in a mass of scratches and pits, suggesting that stone tools were being used as part of food processing, and the teeth were probably being marked accidentally during such activities. Together with Mark Roberts and Simon Parfitt, the leaders of the excavations, and the anthropologists Simon Hillson and Silvia Bello, I was involved in further research on the incisors using a sophisticated imaging microscope, the Alicona.

These studies revealed other, perhaps less routine, activities. The teeth were certainly heavily worn on their crowns, suggesting that this was a middle-aged adult at death, but immediately apparent just below the crowns, much of the roots were coated in the sort of hard plaque that your dental hygienist is likely to remove during checks. This deposition indicates that the roots of these teeth must have been partly exposed above the gums during life, indicating receding gums or, more likely, that the front teeth were being strongly rocked back and forth, probably as they clenched something between them. For many years it has been argued from the strong and rounded wear on their front teeth that Neanderthals indulged in such behavior, and that food, fibrous materials, or skins were being softened or otherwise processed, with clenched teeth acting as a third hand, or a vice.

So it certainly looks like this activity has a much deeper antiquity in Europe, and that many of the cuts and scratches on the Boxgrove incisors were made unintentionally, when a flint tool cut through material being held in the mouth. But the Alicona revealed something else: there was also an unusual series of relatively fresh, deep, and semicircular scratches on the front surfaces of both incisors, evidently made near the time of death with much greater force than the other scratches, and in a completely different direction and action. The roots were also marked by heavy cuts, indicating that these too were made near the time of death. This suggests the possibility that these more violent actions were part of the butchery of this Boxgrove individual around (and we hope for his or her sake after) the time of death.

The famous skeleton discovered in the Neander Valley, Germany, in 1856.

As well as carrying such scars of life and perhaps death, our teeth, as I already explained, contain important signals of our life history in their incremental lines, the dental equivalent of tree rings, which are laid down daily, rather than yearly. These lines have been studied microscopically through their surface expressions—such as the perikymata—but they can also be examined internally through broken surfaces or sections of teeth. I worked in a collaboration with anthropologists including Chris Dean, Meave Leakey, and Alan Walker to examine the growth lines in the molars of several fossil humans, including the Tabun Neanderthal from Israel, when a chip of enamel was briefly removed to apply electron spin resonance dating (see chapter 2) to it. We found that, unlike the pattern in tooth fragments of
Homo erectus
, this Neanderthal did overlap with the fastest developmental rates that we could find in modern molars. In 2007 another team, including Tanya Smith and Jean-Jacques Hublin, studied several teeth from a Neanderthal child from Scladina Cave in Belgium, which in terms of modern human dental development should have been nearly eleven years old when it died. However, their study determined that its actual age at death was only about eight, and the second molar was erupting significantly earlier in the Neanderthal than in modern children, thus signifying a shorter childhood and faster growth than ours.

It was unclear whether these different results regarding Neanderthal maturation were due to inaccuracies in the different methods, to variation between individuals, or perhaps even to evolutionary changes among Neanderthals in their growth patterns. What was most needed to resolve these questions were larger and wider-ranging samples from the fossils. However, as long as microscopic techniques were dependent on having naturally broken teeth or, even less likely, a museum curator willing to have his or her precious fossils sliced up, it seemed unlikely that such samples would materialize. And in terms of nondestructive techniques, only the very finest CT scans—microCT—could even begin to reveal the minute hidden details of incremental lines; so anthropologists have been very fortunate indeed to have yet another technology available to them: the synchrotron.

Many people have heard of the Large Hadron Collider, the world's largest and highest-energy particle accelerator, buried in a tunnel near Geneva, in Switzerland. This is a massive example of a synchrotron, a circular chamber that progressively accelerates atomic and subatomic particles such as electrons or protons, using electrical and magnetic forces. Not far away in Grenoble, France, is a smaller device that is occasionally diverted from the problems of high-energy physics to send its expensive electrons through precious fossils. The 52 kiloelectron-volt synchrotron X-ray beam has already revealed new species of beetles and ants from the time of the dinosaurs, entombed in opaque amber, and even tiny embryos of the dinosaurs themselves, within their mother's eggs. But the technology is now also being applied to hominin fossils such as the skull of
Sahelanthropus
, perhaps an ancestor from over 6 million years ago, and to more recent
erectus
and Neanderthal fossils. Resolution can be fourfold better than the best CT scanners, down to the width of a single cell, and researchers are now queuing up to submit their fossils to the magic of the Grenoble synchrotron.

In one of the first really significant uses of the synchrotron for modern human origins research, some of the team who announced that the Scladina Neanderthal had matured faster than we do were joined by the synchrotron researcher Paul Tafforeau, applying the technology to an early
Homo sapiens
child's jaw. This was from the Moroccan site Jebel Irhoud, and, as I previously described, one of the adult skulls from there was important in my realization that Africa could have been a key region for modern human origins. The Irhoud material is currently dated to about 160,000 years, and could be even older, but opinions differ about the classification of the specimens. In my view, overall, they still lie beyond the range of modern human anatomy and are farther away than specimens of a similar age from African sites like Omo Kibish and Herto.

Jean-Jacques Hublin, however, points to the fact that the child's jaw has a chin, and there are some modern features in the face or braincase of the two adult skulls from the site. But regardless of those debates, the synchrotron study, which combined the counting of external growth lines microscopically with the examination of hidden daily incremental lines using the synchrotron, concluded that this child was about eight when it died and was growing slowly, like a modern child. So even if, as I believe, this was not a fully modern child anatomically, it was already growing its teeth like one, with all the implications that this brings in terms of a prolonged childhood, deferred energetic demands, and an increased capacity for learning.

An early
Homo sapiens
skull from Jebel Irhoud (
left
) and a Neanderthal skull from the cave of La Ferrassie, France.

My museum colleague Robert Kruszynski recently took the Devil's Tower Neanderthal child's skull to Grenoble, and I joined with Tanya Smith, Paul Tafforeau, Jean-Jacques Hublin, and other colleagues in what we hope will be a definitive study of dental development patterns in Neanderthals and early modern humans. Data from many fossils were quantified and analyzed, and nine Neanderthals at different stages of maturity were synchrotroned. These were then compared with similar analyses on five early moderns and a large sample of recent people from different regions. The results seem to finally establish that early moderns such as those from Skhul and Qafzeh were maturing dentally at the slow rate of recent humans, while the Neanderthals were growing somewhat faster, particularly in the case of the later erupting teeth. Thus, for example, the Neanderthal children from Engis, Scladina, and Le Moustier should have been about four, eleven, and sixteen years old respectively from modern development patterns, but the synchrotron showed that they were actually about three, eight, and twelve. Not only were the Neanderthals maturing faster, but the more rapid growth of their molars meant that these teeth had thinner enamel than ours. As we will see, such differences in life histories may have been significant in the distinct social structures and cultural development of Neanderthals and modern humans.