A discovery in southern China of human teeth dated to more than 80,000 years old indicates that Homo sapiens was present in the region considerably earlier than had previously been suspected. See Letter p.696
Debate over when our species, Homo sapiens, first dispersed from Africa across southern Asia is hindered by a lack of relevant fossil evidence between the eastern Mediterranean and southeast Asia. Exciting new material is presented in this issue by Liu et al.1 (page 696), who describe a collection of H. sapiens teeth from a cave in southern China's Hunan province. The age and morphology of the teeth suggest that modern humans reached southern China long before they had arrived in northern China or in Europe.
Most researchers agree that our species first appeared in East Africa around 190,000 to 160,000 years ago, and then dispersed into the eastern Mediterranean around 100,000 to 60,000 years ago, after which it was replaced by Neanderthals. Following this apparent 'failed dispersal'2, one suggested scenario is that H. sapiens did not progress eastwards until around 60,000 years ago — a date based on the estimated divergence time of genetic lineages in South Asian people3 and the probable arrival date of humans in Australia4. This picture is supported by apparent similarities between small stone tools known as microliths from South Africa dating to around 60,000 years ago and ones from South Asia that are between 30,000 and 36,000 years old3,5. These similarities have been interpreted as showing a direct link between the earliest modern humans in South Asia and their probable African ancestors5, although the similarities now seem less robust than was first argued6. A contrasting scenario is that H. sapiens first dispersed eastwards (probably by way of the Arabian Peninsula) during the last interglacial period, and entered South Asia well before 60,000 years ago, and perhaps before the volcanic super-eruption that occurred 74,000 years ago at present-day Lake Toba in Indonesia7,8,9.
One place where these hypotheses can be tested is in southern China, which is dotted with karst caves that are rich fossil sources. But descriptions of this material have so far been ambiguous because of doubts over the stratigraphic context of skeletal specimens, their dating and/or their identification. Some finds were made by villagers while digging for fertilizer, which obscured the stratigraphic context of the fossils; in other cases, fossil teeth are too worn for identification purposes, or the association between a dated flowstone deposit and a skeletal specimen is unclear10. At Zhiren Cave in southern China, for example, a mandible (lower jawbone) attributed to H. sapiens was found in a geological sequence dated by five flowstones ranging from 110,000 to 55,000 years old11, so the specimen may be younger than the published age of 110,000 years12; it has also been suggested that the mandible is from a late Homo erectus individual13.
Liu and colleagues' discoveries at Fuyan Cave are especially welcome because they seem to lack these usual problems surrounding context, dating and identification. A flowstone (layer 1) covers the entire cave floor, so the underlying material clearly has to be older; a stalagmite on this flowstone was dated to a minimum age of 80,100 years old (± 1,200 years). The underlying layer 2 is a thin, sandy clay around 20–50 centimetres thick, in which the authors identify numerous mammalian fossils from 38 extant species and 5 extinct large mammals. This fauna is identified as being from the Upper Pleistocene period (125,000 to 10,000 years ago), so the human teeth, which were found in layer 2 in part of the cave, are estimated to be between 80,000 and 120,000 years old.
The teeth are well preserved and show detailed cusp morphology. All 47 are unequivocally attributed to H. sapiens. The authors describe them as generally smaller than other African and Asian specimens from the Upper Pleistocene, and closer in size to those of Upper Pleistocene Europeans and contemporary modern humans. The M1 molar teeth in the sample are different in shape from the rhomboidal contours displayed by Neanderthals or the elongated teeth seen in Asian H. erectus fossils. Instead, the relative cusp and occlusal polygon areas of the M1 molars are almost identical to those of modern Chinese populations. They also seem less primitive than northern Chinese specimens such as those discovered at the Xujiayao site14.
This discovery has several implications. The finding that H. sapiens first appeared in southern China between 120,000 and 80,000 years ago indicates that our species dispersed across southern Asia well before 60,000 years ago (Fig. 1). Furthermore, the fact that the teeth resemble those of Upper Pleistocene Europeans and modern humans implies that the population they came from were immigrants and not the outcome of local evolution from H. erectus. To place these finds in their continental context, the Fuyan teeth indicate that modern humans were present in southern China 30,000 to 60,000 years earlier than in the eastern Mediterranean and Europe. This is not surprising, perhaps. H. sapiens originated in or near the tropics, so it makes sense that the species' initial dispersal was eastwards rather than northwards, where winter temperatures rapidly fell below freezing. As Liu and colleagues point out, the finds also imply that modern humans were in southern China long before there is evidence for them in northern China and Europe. In the case of northern China, the earliest evidence is from Tianyuan Cave near Beijing, dated to around 40,000 years ago15; in Europe, evidence appears around 45,000 to 40,000 years ago16. Here, the authors suggest, the presence of Neanderthals may have delayed the arrival of modern humans. However, the predominantly colder winter conditions of the enormous landmass between Europe and northern China may better explain the earlier colonization of southern zones.
Excavation of other caves in the region will undoubtedly add to the findings from Fuyan. What is especially needed now is archaeological evidence (sadly lacking in Fuyan Cave) to indicate whether the initial dispersal of our species was caused or facilitated by cognitive developments (such as symbolism or complex exchange systems), or was simply an example of opportunistic range extension. More revelations about our species' history can surely be expected from southern China.
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Nature Ecology & Evolution (2018)