A piece of jawbone excavated from a prehistoric cave in England is the earliest evidence for modern humans in Europe, according to an international team of scientists. The bone first was believed to be about 35,000 years old, but the new research study shows it to be significantly older -- between 44,000 and 41,000 years old, according to the findings that will be published in the journal Nature. The new dating of the bone is expected to help scientists pin down how quickly the modern humans spread across Europe during the last Ice Age. It also helps confirm the much-debated theory that early humans coexisted with Neanderthals.
Beth Shapiro, the Shaffer Associate Professor of Biology at Penn State University and a member of the research team, explained that the fragment of maxilla -- the upper jaw -- containing three teeth was unearthed in 1927 in a prehistoric limestone cave called Kent's Cavern in southwestern England. Records from the original excavations, undertaken by the Torquay Natural History Society located in Devon, England, indicate that the jawbone was discovered 10 feet 6 inches beneath the surface and was sealed by stalagmite deposits. "In 1989, scientists at Oxford University dated the bone as being about 35,000 years old. However, doubts were later raised about the reliability of the date because traces of modern glue, which was used to conserve the bone after discovery, were found on the surface," Shapiro said. "We knew we were going to have to do additional testing to re-date the bone." Because the remaining uncontaminated area of bone was deemed too small to re-date, the research team searched through the excavation archives and collections in the Torquay Museum to obtain samples of other animal bones from recorded depths both above and below the spot where the maxilla was found.
Members of the research team then obtained radiocarbon dates for the bones of wolf, deer, cave bear, and woolly rhinoceros, all of which were found close to the maxilla and all which could be dated at between 50,000 and 26,000 years old. Using a Bayesian statistical-modelling method, the scientists then were able to calculate an age for the maxilla. The new date indicates that the bone is between 44,000 and 41,000 years old.
Tom Higham, Deputy Director of Oxford University's Radiocarbon Accelerator Unit and a member of the research team, said "Radiocarbon dating of ancient bones is very difficult to do. Because the initial date from this fragment of jawbone was affected by traces of modern glue, the initial measurement made in 1989 was too young. The new dating evidence we have obtained allows us, for the first time, to pinpoint the real age of this key specimen. We believe this piece of jawbone is the earliest direct evidence we have of modern humans in northwestern Europe."
Shapiro explained that the new and more-accurate date is especially important because it provides clearer evidence about the coexistence of Neanderthals and anatomically modern humans. "If the jawbone is, in fact, 44,000 to 41,000 years old, that means it was from a time when Neanderthals were still present in Europe, so we first had to confirm that the bone was from an anatomically modern human, and not a Neanderthal," Shapiro said. Shapiro and her team first tried to extract mitochondrial DNA from one of the teeth, but there were insufficient amounts for valid DNA sequencing. Eventually, team members were able to use a virtual three-dimensional model based on a CT scan of the jawbone to carry out a detailed analysis of the fossil. They compared the external and internal shapes of the teeth with those of modern human and Neanderthal fossils from a number of different sites. They found early modern human characteristics in all but 3 of the 16 dental characteristics.
Studies of the maxilla have been underway for the last decade, but it was only with the application of the latest investigative and dating techniques that the research team was able to make this breakthrough in identifying the jawbone as the earliest modern human so far known from Europe. "Comparative data were lacking for some of the traits our team was studying," Shapiro said. "So, thankfully, our team member Tim Compton of the Natural History Museum in England helped by building a completely new database to help discriminate modern features from Neanderthal features. While the dominant characteristics are certainly modern, there are some that are ambiguous, or that fall into the Neanderthal range." The research team believe that these ambiguous features may reflect inadequate sampling of modern human variation, shared primitive features between early modern humans and Neanderthals, or even interbreeding between the two species. "We'll have to delve a little deeper and do more work to resolve these questions," Shapiro said.
Another exciting feature of the new study is that it could help solve the apparent discrepancy about the known dates of the Aurignacian period -- a time of cultural development in Europe and southwest Asia that lasted from around 45,000 to 35,000 years ago. Previous researchers have discovered artefacts and tools from this period that are thought to have been produced by the earliest modern humans in Europe. However, strangely, these artifacts have been found to be much older than the rare skeletal remains found in the same vicinity. While Aurignacian tools and ornaments have been dated at as old as 44,000 years, tests to pinpoint the age of relevant human remains have resulted in dates that reach no further than between 41,000 and 39,000 years ago, indicating a significant gap.
"The new date and identification of this bone from Kent's Cavern is very important, as we now have direct evidence that modern humans were in northwest Europe about 42,500 years ago," Higham said. "It confirms the presence of modern humans at the time of the earliest Aurignacian culture, and tells us a great deal about the dispersal speed of our species across Europe during the last Ice Age. It also means that early humans coexisted with Neanderthals in this part of the world, something that a number of researchers have doubted."