A publication of the Archaeological Institute of America
Virtual fossils and real molecules are changing how we view our enigmatic cousin.
Next year will mark the 150th anniversary of the discovery at Neandertal, a little valley near Duesseldorf in western Germany, of the first recognized fossil humans. The occasion will be commemorated with conferences and exhibitions at major German museums. As a warm-up for this "Neandertal Year," two dozen scholars gathered at New York University this past January, in a Manhattan suffering near-glacial conditions, to exchange views on the latest advances in the field.
Our fascination with Neandertals is well founded. They were the first known example of an extinct species of human, they evolved mostly in Europe, and we now have an unrivaled fossil record accumulated by a century and a half of research. Because there are more specimens of Neandertals than any other premodern human, any new techniques or approaches in paleoanthropology are usually applied to them first. And in recent years we have learned a great deal about these humans that once seemed unattainable, including aspects of their biology such as genetics. Studies have also revealed unexpected features of their growth, development, and life history. Even more traditional approaches, such as the comparison of Neandertal and modern human bone shapes, continue to yield new data.
Visions of the Neandertals as brutish cave dwellers prevailed for many years following their discovery. The first reconstruction, in 1908, was based on the partial skeleton of an old male found at La Chappelle aux Saints in France, but the individual had been stooped from arthritis. That fact, and its projecting face, heavy brow, and generally robust bones gave rise to our earliest, though inaccurate, view of Neandertals. But in the last decades of the twentieth century, the pendulum began to swing in the opposite direction. For some, Neandertals appeared only as a slightly different population of our own species, adapted to the cooler climates of the Paleolithic world. The most politically correct version saw them as almost indistinguishable from modern humans in abilities and behaviors, and hardly differing in many anatomical aspects. The New York conference provided a more balanced picture of a "New Neandertal" that is both very similar to and very different from us.
Emblematic of this New Neandertal is a composite skeleton created at the American Museum of Natural History in New York and discussed at the conference by Ian Tattersall, one of its curators. Most scholars have focused on analyzing particular parts of the skeleton, such as the skull or pelvis, so the reconstruction is our first look at an entire one. It is a large male, built from casts of bones from several individuals (most are from two finds, one at La Ferrassie, France, and the other at Kebara, Israel). Tattersall emphasized how different it is from our own skeletons, not only in the anatomy of the skull, which is well known, but in entire body shape. If any living Neandertals had come to the conference dressed in a suit and tie, they still would have stood out. But this composite skeleton was only one of many innovative approaches to finding the new Neandertal that were presented in New York.
Human fossils are precious and fragile, and to study them scientists have embraced or developed new methods in recent years. CT scanning, for example, is used with increasing frequency to assess fine internal details of specimens, such as the inner ear of Neandertals. Imaging techniques, combined with sophisticated software for manipulating digitized fossils, allow us to work with virtual objects rather than the originals. One can now reconstruct fragmentary specimens, piecing them together on the computer and supplying missing parts. If a skull's right side is damaged, the left can be copied and a mirror image of it substituted instead. Even specimens warped and distorted in the fossilization process can be straightened out.
The new methods of "virtual paleoanthropology" have been used to investigate how modern humans and Neandertals differ even in childhood. At the New York meeting, Marcia Ponce de Leon and Christoph Zollikofer of the University of Zurich presented a computer model and simulation comparing skull growth, showing the divergence of shape began early in development and reflected different growth patterns in the bones. Another comparison of Neandertal and modern human childhood development was recently undertaken by Fernando Ramirez-Rozzi of the French Centre National de la Recherche Scientifique in Paris and Jose Maria Bermudez de Castro of Madrid's Natural History Museum. They looked at tooth enamel, which has microscopic striations that can be counted like the growth rings in a tree trunk, and concluded that Neandertals reached adulthood at about 15 rather than 18 years of age, as in present-day human populations. Further analysis will confirm whether or not this was the case.
Modern human specimens are also being digitized, allowing us to assess bone shape and size variations and understand their significance in anatomical evolution. In a remarkable contribution at the conference, Katerina Harvati and Tim Weaver of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, looked at skull variation in modern humans from different climates and cultures. They found that the shape of the face is linked to local environmental conditions, which fits well with the current belief that the Neandertal's projecting face is a cold-climate adaptation. By contrast, the shape of the brain case, particularly the temporal bone (on the side of the skull), proved to be a good indicator of genetic closeness among populations.
Meanwhile, the genuine specimens have been the object of increased attention through the study of DNA, proteins, and chemical elements that can be found in bones and teeth--giving us a completely new source of valuable information about our remote relatives' biology and their daily lives.
In 1997, a fragment of DNA was reconstructed from the same bones that the quarry workers found in Neandertal in 1856. The DNA of the Neandertal fell outside modern human variation, and suggested a divergence between the ancestors of Neandertals and modern humans nearly half a million years ago. Since the original DNA study, nine other Neandertal individuals have yielded some genetic information, all similar to one another yet distinct from that of modern humans. Although this number is small, the evidence gives us insight into the demography of the Neandertals. The limited variability of their DNA suggests that there were times, perhaps during glacial advances, when their population was greatly reduced, resulting in genetic bottlenecking. The population recovered in size afterward but with fewer surviving different genetic lines. In this respect, humans--modern, Neandertal, and others--strongly contrast with African apes, which evolved in a much less stressful environment during the last several hundred thousand years, and therefore have much greater genetic variability.
Interestingly, while we can now study Neandertal DNA, it is very difficult to analyze DNA from the early modern humans who replaced them between 40,000 and 30,000 years ago. Because Neandertal DNA is different from our own, modern contamination (from excavators, museum curators, or laboratory personnel) can be identified and discounted. With fossils of our own forebears, however, differentiating ancient DNA from recent contamination is virtually impossible. Such research can only be undertaken with new fossil finds that are kept in sterile conditions from the field to the lab.
There is no evidence that the last Neandertals were evolving toward a physical appearance like our own, but the issue of the possible contribution of Neandertals to the modern European genetic makeup is still fervently debated. Even if Neandertals represented a distinct, although very close, species separate from modern humans, we know that in nature, hybridization is a common process under such circumstances. At the conference, Trenton Holliday of Tulane University surveyed the zoological evidence, pointing out many hybrids among large mammals including members of the camel, horse, dog, and cat families. Did Neandertals and modern humans interbreed? It is quite possible in some instances, but it had no major biological results.
Proteins can now be recovered from bones and examined with methods similar to those used with DNA. This year, for the first time, Christina Nielsen-Marsh of the Max Planck Institute was able to extract and analyze a protein from Neandertal teeth from Shanidar, Iraq. In Neandertals, this particular protein (osteocalcin) displays a sequence similar to that of modern humans, indicating it has changed little over a long period of time. In the near future, extraction and sequencing of fossil proteins may open new ways to study evolutionary relationships between extinct species, and may allow us to go farther back in time than is possible with ancient DNA, which is more complex and degrades more quickly.
Scientists are investigating other molecules and chemical elements found in Neandertal bones. Collagen, routinely extracted from bone today for radiocarbon dating, yields carbon and nitrogen, while strontium and calcium can be sampled from the mineral parts of bone. These four elements can give us indications of an individual's diet, since they come from foods. Studies by Herve Bocherens of the Centre National de la Recherche Scientifique in Montpellier and Michael Richards of the Max Planck Institute suggest the European Neandertals were highly carnivorous, a pattern not unlike that observed in modern hunter-gatherers in cold regions. In the future, such analyses may also reveal indicators of population movements, since bone chemistry also reflects, for example, specific elements in ground water that vary from region to region.
The Last Neandertals
The possible interactions between Neandertals and modern invaders between 40,000 and 30,000 years ago in Europe remains one of paleoanthropology's most debated issues, so it was no surprise that it surfaced in New York. There is little doubt that the presence of another group of humans in Europe played a major role in the extinction of the Neandertals, through competition for resources if nothing else. But other factors in the Neandertals' demise have been discussed recently. For example, Chris Stringer of the Natural History Museum, London, has shown that this period was characterized by repeated and extreme climatic changes occurring in rapid succession. Although Neandertals had faced and survived severe climatic crises along the course of their evolution, the coincidence of this climatic instability with the invasion of the European territory by modern humans presented a double challenge for the last Neandertals. Both groups must have tried adapting during this confrontation in a very difficult environment. At the conference, Shara Bailey of the Max Planck Institute and I showed that Neandertals at the French cave site of Arcy-sur-Cure are indisputably associated with stone tools and bone ornaments formerly thought to have been made only by modern humans. The acquisition during this period of new techniques and habits, such as the use of body ornaments, by the last Neandertals is much debated by specialists. Many scholars believe it may have resulted from their encounters with modern humans, who had developed this behavior more than 100,000 years ago, even before leaving Africa. These contacts, they argue, may have been seldom, but resulted in imitation by the Neandertals or even trade between the two populations. But modern humans might have been affected as well. It has been proposed that the burst of artistic expression--cave art, figurines, and the like--observed in our forebears at this time relates to group identification and may have resulted from the interaction with these indeed human, but very different, beings.
Because Neandertals are the best-known group of fossil humans, they are the group that always raises the most questions. As the last branching of the human evolutionary tree and our closest relatives in the recent past, they will remain an object of popular fascination as well as scientific interest. In fact, how we envision Neandertals may tell us as much about the way we see ourselves as about them. With the "New Neandertal" we have definitively shed two such images, one in which our ancient cousin was brutish and far different from us, the other in which we were nearly identical. But perhaps our new-found knowledge, from virtual fossils and molecular studies, is taking us to a deeper understanding of Neandertals.
Jean-Jacques Hublin, director of the Department of Human Evolution at the Max Planck Institute in Leipzeig, has led fieldwork in France, Spain, and Morocco, and is now participating in an international project at Dikika, Ethiopia.