The ongoing debate about when and how anatomically modern humans ("AMH") made their presence in east Asia has taken another turn with new evidence recovered from a cave in central China. The finds may push back the generally accepted time of their appearance in the region by as much as 50,000 years.
A team of six researchers from four institutions, using high-precision mass spectrometric U-series dating techniques, were able to determine a reliable and constrained date range of between 81 and 101 ka (thousand years) for seven human fossil teeth recovered from the Huanglong Cave in the Hubei Province of central China. The teeth, determined to exhibit anatomically modern human characteristics, were revealed in a layer associated with stone tools and other fossilized animal remains during excavations conducted in 2004, 2005 and 2006 by a joint team from the Hubei Provincial Institute of Cultural Relics and Archaeology and the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences. The excavations were followed by further fieldwork in 2010 and 2011.
Reports Guangun Shen, et al., "the existence of localized thin flowstone formations bracketing the hominin [ancient human] fossil-bearing deposits enables us to firmly constrain the human teeth into the range between 81 ka and 101 ka, probably the most narrow time span for any hominin fossil beyond 45 ka in China".* Flowstones are sheetlike deposits of calcite formed over many thousands of years, the result of water flowing down the walls or along the floors of caves. They are a type of speleothem, or secondary mineral deposit such as a stalagtite or stalagmite, often found in ancient cave systems.
According to the study authors, the finding comes after a series of other relatively recent excavations and reports that have produced "a growing body of evidence for the possible presence of AMH in eastern Asia as early as 100 ka ago".* They refer here to some limestone caves in southern China where scientists have come up with more ancient dates, including Liujiang (between 111 and 139 ka), Ganqian (between 94 and 220 ka), Bailiandong (more than 160 ka), and Zhirendong (more than 100 ka) in Guangxi. The Guanglong Cave results, however, are considered the most reliable because of the much narrower constraining range of 81 to 101 ka as determined by the latest U-series dating technology.
These new findings have challenged the prevailing theory among scientists that anatomically modern humans were not present in China or east Asia until roughly around 40,000 - 50,000 years ago. This is based on earlier findings at a number of sites across China and east Asia that point to a ‘gap’ between 100 ka and 40 ka ago lacking any human fossils, more specifically between the latest archaic humans and the earliest modern humans, and genetic studies of present-day Chinese populations that have suggested a late appearance of AMH in eastern Asia.
But this previous data, maintains Shen, et al., was generated using older, less reliable dating techniques and excluded fossils claimed to represent AMH. "Based on our work on the sites of H. erectus (an earlier form of human) and of both archaic and modern H. sapiens over the past twenty plus years, we argue that the temporal framework in China has been artificially ‘compressed and gapped,’meaning that due to limitations in previous dating techniques and practices, the ages of Chinese hominin fossils have been significantly postdated (compressed), and that a temporal gap between archaic H. sapiens and AMH has been artificially created (gapped)."*
Regarding the genetic studies, they argue that "more solid skeletal discoveries, along with parallel studies in relevant disciplines are needed to reconcile the geochronology and the molecular clock."*
Perhaps even more significant, the researchers suggest that the entire timeline for hominin (ancient human) presence in east China should be shifted back earlier in time and should be continuous (without the gap), based on updated research. This includes the advent of H. erectus at more than 400 ka old, rather than the current 230 ka; archaic H. sapiens at more than 200 ka, instead of ca. 110 ka; and the emergence of AMH at around 100 ka or earlier.
Concludes the team: "The newly established timeline for hominin fossils in China, as a result of more meticulous stratigraphic work and the advancement in dating techniques, demands a reexamination of hominin fossils and associated materials in a more coherent chronological context in China."*
Details of the study have been published in the August 2013 issue of the Journal of Human Evolution as Mass spectrometric U-series dating of Huanglong Cave in Hubei Province, central China: Evidence for early presence of modern humans in eastern Asia.