Lone Survivors (13 page)

At an even finer level of our physiology than daily growth lines in our teeth, our bodies are built and maintained from the nutrition that we take in every day from food and drink. In that sense the old macrobiotic slogan “you are what you eat” is absolutely accurate. The many different chemicals in our foodstuffs are taken up into our bones and teeth and, if those are preserved as fossils, they can provide signals that can be interpreted as evidence of former diets. As mentioned in the previous chapter, atoms of substances such as carbon and nitrogen (two vital components of our bodies) come in the form of distinct isotopes, which have different atomic weights (because they contain different numbers of particles called neutrons). Although the essential properties of these slightly different atoms remain constant—for example, in the chemical compounds they can form—the compounds may behave somewhat differently when they are subjected to heat, say, where lighter isotopes may be preferentially evaporated. When compounds are taken up or pass through living systems, the rate at which this happens may vary between lighter and heavier isotopes. Carbon and nitrogen both have stable isotopes (that is, they do not undergo radioactive decay as the isotope carbon-14 does). These stable isotopes are found in collagen, a fibrous structural protein that makes up much of our body tissues and bones. Although bone and the collagen in it are constantly renewed as a living tissue, the turnover is quite slow, and stable isotope data from collagen will represent an average of diet over the last decade or more of an individual's life. Collagen is lost as a bone fossilizes, but enough can still be preserved in remains that are less than 100,000 years old for its constituent isotopes to be measured.

The relative abundance of the stable carbon isotopes C-13 and C-12 varies in different ecosystems, such as on land or sea, and also between different kinds of plants, so animals that feed from these different sources will pick up different ratios of the isotopes, according to their diets. In addition, the relative abundance of the stable nitrogen isotopes N-15 and N-14 increases by about 2 to 5 percent in each step up the food chain (for example, in moving from grass to the rabbit that eats it, and then to the human that eats the rabbit). So by simultaneously measuring carbon and nitrogen isotope ratios in the fossil bones of, say, a Neanderthal, it is possible to reconstruct something of that individual's diet during his or her life. The isotopes will not reflect everything, since the signals represent the main dietary protein sources rather than all foods consumed, and, as mentioned, the isotope uptake is also averaged over the last years of life. In addition, only broad categories such as the predominance of plant, herbivore, and carnivore protein derived from terrestrial or marine ecosystems can be distinguished. Care also has to be taken in analyses, as there is evidence that differences in climate such as temperature and aridity can affect the underlying stable isotope ratios, and thus the most reliable comparisons are on material relatively close in time and space.

Nevertheless, despite all these provisos, valuable insights into ancient diets have been obtained from the bones of both Neanderthals and early modern humans by researchers like Michael Richards and Hervé Bocherens. Over a dozen Neanderthals and even more Cro-Magnons have been analyzed, and clear patterns have emerged that confirm our view that the Neanderthals were heavily dependent on meat from large game such as reindeer, mammoth, bison, and horse. They were at the top of their food chains, and their isotope signatures place them with wolves and lions as the dominant predators in their landscapes. However, the fossils analyzed come from regions like France, Germany, and Croatia, and do not yet cover the whole Neanderthal range—unfortunately, warmer regions like Gibraltar and the Middle East have poorer collagen preservation. And we know from archaeological data that farther south, in the coastal regions of Portugal, Spain, Gibraltar, and Italy, the Neanderthals were supplementing their big game with marine resources such as shellfish, seals, and, at least occasionally, dolphins that had probably been stranded. Although the isotope signal would have been obscured if meat was the dominant source of protein, where conditions and the seasons allowed, plant resources were also important to them, as burned nuts and seeds in the cave deposits show.

The 40,000-year-old Oase fossils.

But analyses of the Cro-Magnons, including the rather primitive 40,000-year-old Oase early moderns from Romania (see the next chapter), present a different dietary picture to that of the Neanderthals, even when comparisons are limited to the same regions and climates. High levels of C-13 in some of the samples near coastlines suggest a menu that included significant quantities of marine fish or other seafoods, while those that lived farther inland may have had even more diverse diets, since unusually high levels of N-15 in their bones suggest that fish, waterfowl, and other freshwater resources provided important sources of food. And the fact that this was already the case in the oldest modern human sampled, from Oase, becomes even more significant when we look at another modern fossil of similar age over 6,000 kilometers away in China: the adult skeleton from Tianyuan Cave, recently excavated in the Zhoukoudian complex of sites. (This skeleton is further discussed in the next chapter.) Carbon and nitrogen isotopes in collagen extracted from the bones indicated a diet high in animal protein, but the very high nitrogen isotope ratio also suggested the consumption of freshwater fish. Sulphur isotopes were then measured in terrestrial and freshwater animal remains from ancient and recent archaeological sites in the Zhoukoudian area to give a baseline comparison for this additional dietary indicator, and when the sulphur values were analyzed for the Tianyuan skeleton they confirmed a substantial portion of this individual's diet must have been made up of freshwater fish.

So with the very earliest evidence we have of modern humans in their dispersal from western Asia into Europe and into the Far East, the abilities of
Homo sapiens
were already apparent in the extraction of more nutrition from their environments than the Neanderthals could achieve, and this was surely one of the keys to our survival and eventual success in the challenging environments of the north. The ratio of two other stable isotopes, of strontium (Sr-87 and Sr-86), may also help us track some of the migrations of those early humans, as the relative proportions of these isotopes vary in the different ground rocks through which water flows. When animals, including humans, ingest these isotopes in their diet or drinking water, they are taken up into the bones and teeth in the same way that calcium is, and thus provide a marker of where an animal had been living at the time or earlier in life. Tooth enamel will preserve an indicator from childhood, while bones, with their turnover, will record a signal from the last few years of life, so by comparing the isotope ratios in a fossil skeleton with those in the rocks of the surrounding landscapes, it is now theoretically possible to “locate” a Cro-Magnon to, say, its local limestone area or perhaps to granite hills many kilometers away, where that individual may have lived as a child. And if that Cro-Magnon was eating reindeer, it would be possible to map the migrations of those reindeer herds from their remains in the same archaeological site. This technique is now becoming feasible for precious fossils because, with improvements in technology and measurement, laser ablation can produce isotope results from even minute fragments of enamel.

Teeth and bones contain many clues to the life histories and activities of long-dead people. Having discussed how new technologies are helping us to date and investigate important relics, let us now turn back to the fossil record itself, to pick up the developing story of the origin of our species.

4

Finding the Way Forward

In chapter 1 I showed how RAO went from being a view that no one held in 1970 to the dominant model for modern human origins in an astonishing period of less than thirty years, and I laid out the standard rapid African origin, expansion, and replacement view that people like me began to develop and hold from around 1984. Now I'd like to look at how some elements of the early part of that scenario are taking on a different significance, challenging the orthodoxy of Out of Africa 1, with implications for our own ultimate origins.

In 1991 surprising new finds started to be made in western Asia, at Dmanisi in Georgia. An ancient village on a hill was being excavated by medieval archaeologists when they discovered the remains of a rhinoceros jaw in the cellar of one of the buildings. This was just about explicable if a traveler had brought or traded a specimen back from Africa or Asia, but expert opinion determined that it was actually a fossil rhinoceros, perhaps a million years old, and that was a lot more difficult to explain! It turned out that the village had, by chance, been built on a much more ancient fossiliferous deposit, and once the medieval archaeologists and the paleontologists had agreed how the site could be dug to the satisfaction of both parties, new excavations got under way. Pleistocene fauna was found, then a human lower jaw and primitive stone tools. Georgian workers and their foreign collaborators argued that the site was potentially about 1.8 million years old, but everyone else was cautious, since such an age challenged prevailing views, and when we got our first sight of the fossil at a conference in Frankfurt in 1992, most of us thought that the jaw seemed too evolved for such a great age. However, two Spanish researchers, Antonio Rosas and José María Bermúdez de Castro, reported that the jawbone resembled both early
erectus
specimens from East Africa and later
erectus
material from China. Further excavations and research amply confirmed the original claims, placing the date at about 1.75 million years, and producing five small-brained human skulls, three more jawbones, many other parts of the skeleton, and a quantity of very basic stone tools, often made from local volcanic rocks. These finds were, and still are, challenging, as it used to be thought that the first move out of Africa was enabled by changes in behavior, increasing brain size, or better tools—and none of those developments seem to be evidenced at Dmanisi. Some of the animals had probably dispersed from Africa, including two large saber-tooth cat species. These specialized animals lacked the teeth to strip a carcass clean of its meat or break the thicker bones of their prey, so they potentially provided scavenging opportunities for the early humans from what they left behind. But wider comparisons of the animal species suggest that the Dmanisi assemblages most closely resembled those of the grasslands and woodlands of southern Europe at that time, supporting the idea that these early non-Africans had already adapted to new environments.

The second find I am going to discuss presents even greater challenges to conventional thinking on human evolution, so much so that one expert implied it is more like the Piltdown hoax than a genuine fossil relic! It used to be thought that only one species of early human lived in southeast Asia before modern humans arrived there: the ancient species
Homo erectus
, best known from the island of Java, as we saw.
H. erectus
could have reached Java from southern Asia at times of lower sea level, when the islands formed part of a larger ancient landmass that scientists have called Sunda (from an Indonesian word for western Java). Without boats,
erectus
could get no farther. Thus it was generally believed that Java/Sunda represented the farthest limit of human colonization in the region until modern humans arrived, perhaps 50,000 or 60,000 years ago, who were able to use boats to disperse even farther, toward Australia and New Guinea. But in 2004 remarkable evidence was published by the Australian archaeologist Mike Morwood and his team of a new humanlike species from the island of Flores, about five hundred kilometers east of Java. The remains included much of the skeleton of an adult estimated to be only about a meter tall, with a brain volume of about four hundred cubic centimeters (about the same as that of a chimpanzee). This find and other more fragmentary specimens were discovered in Liang Bua Cave on Flores, associated with stone tools and the remains of a pygmy form of an extinct elephant-like creature called
Stegodon
. The skeleton was dated to only about 18,000 years ago and was assigned to a new species called
Homo floresiensis
(“Flores Man”), but it soon became better known by its nickname “the Hobbit.”

I was privileged to be chosen as the main commentator at the press conference in London that launched the startling new find to the world, but it was unexpected for so many reasons. It lay five hundred kilometers of islands and water beyond the accepted range of ancient humans, implying that the Hobbit's ancestors must have had boats to get there; it seemingly had a “human” face and teeth, and walked upright, yet it had an ape-sized brain; despite its small brain it was associated with stone tools and possible evidence of hunting and fire. If it was a distinct species, where did it come from, how did it survive long after other forms like the Neanderthals, and what happened to it after 18,000 years ago? There was immediate and fierce controversy about the nature of the finds, and whether they had been correctly interpreted. Some scientists insisted that they were wrongly dated and might represent small-bodied modern humans; others argued that the unusual features were signs of disease, perhaps due to medical abnormalities such as microcephaly, cretinism, or a condition called Laron syndrome. The situation was exacerbated when the late Teuku Jacob, an esteemed but retired Indonesian paleoanthropologist (who was a Hobbit skeptic, and not part of the original research team), “borrowed” the finds in order to conduct his own studies. When they were eventually returned, in the face of vigorous protests, some of the bones had been seriously damaged, apparently through hurried and botched attempts to replicate them.