The hominin invasion of China

Earlier this month, Scientific Reports included an article by Hong Ao and colleagues reporting a date for the Shangshazui archaeological locality in the Nihewan Basin of North China Ao:2013. This is now one of the earliest sites known for human activity in China, possibly the earliest, between 1.7 million and 1.6 million years ago.

The dating of this site is part of a much larger story of archaeological dating in China. Early Pleistocene sites, particularly in the Nihewan Basin west of Beijing, have given rise to a much more detailed paleomagnetic stratigraphy allowing them to be placed more accurately in time. As a result, China now has several archaeological sites dated to before 1.5 million years ago, with the earliest known occupation within a hundred thousand years of the Dmanisi hominins.

Knowing the precise age ranges of early hominid habitation and stone technologies in different regions of the world is a key component for a comprehensive understanding of human evolution. The Nihewan Basin in North China is an intermontane basin about 150?km west of Beijing (Fig. 1). It comprises one of the most detailed sets of Early Pleistocene Paleolithic evidence from the whole of Asia1. Therefore, it has become a major area of archaeological research and a prime focus of investigations into early human evolution in East Asia. During the past decades, more than 60 Paleolithic sites associated with thousands of in situ Oldowan-like stone tools (i.e., Mode 1 core and flake technologies) were found in the basin. The Nihewan fluvio-lacustrine sediments do not contain material suitable for radio-isotopic dating (e.g., tephra). The exact ages of these Paleolithic sites thus have long been considered controversial. Only recently, reliable ages were assigned to some Early Pleistocene Paleolithic sites based on high-resolution magnetostratigraphy; sites include Majuangou (MJG) dated at 1.661.55?Ma, Lanpo (LP) at 1.6?Ma, Xiaochangliang (XCL) at 1.36?Ma, Xiantai (XT) at 1.36?Ma, Banshan (BS) at 1.32?Ma, Feiliang (FL) at 1.2?Ma and Donggutuo (DGT) at 1.1?Ma. These recently established magnetostratigraphic ages of the Paleolithic sites in the basin have dramatically increased our understanding of early human colonization of 40 N East Asia.

Majuangou was reported in 2004 by Zhu and colleagues Zhu:2004, and was the first of the archaeological sites to break 1.5 million years ago. The site includes horse bones with percussion marks, where they were broken for marrow extraction. Zhu and colleagues reported later, in 2008, on new dating for the Yuanmou site in southern China, which has produced two central incisors of an ancient human (presumably Homo erectus) and stone artifacts. Their date estimate, 1.7 million years ago, is as early as estimated in this new paper for Shangshazui in northern China.

The Early Pleistocene is not the only time period that has been revolutionized by recent dating efforts in China; many Late Pleistocene sites have also been redated in the last few years. But the Early Pleistocene is simpler to understand: an earlier chronology in China puts that region in alignment with Java and Georgia in pointing to a rapid hominin invasion of Asia.

Ao and coworkers Ao:2013 consider an ecological explanation for the rapid movement of humans across Asia:

Consistent with the dispersal of Proboscidea out of Africa at 2.51.5?Ma, Hipparion sp. was also found in the Nihewan Basin during the Early Pleistocene. Therefore, favorable global (especially Africa and Eurasia) climatic and environmental conditions make it not illogical to expect to find hominid emigrants in the Nihewan Basin at ca 1.71.6?Ma: similar mixed savanna and woodland habitats as in Africa and southern Caucasus are shown to be present here.

In this brief rendering, it is the similar ecological context across parts of Asia that humans followed rapidly, along with other African fauna. By contrast, Zhu and colleagues looked to a broader environmental range in their 2008 article about the Yuanmou finds Zhu:2008.

The similarity of age constraints (1.701.66 Ma) currently defined for different areas of eastern Asia may yield, however, a more robust hypothesis concerning this novel extension of the geographic range of Homo. Early Homo at Yuanmou lived near the time of a wide expansion of East Asian hominins over an area that extended from at least 40N (Nihewan Basin) to 7S (Java) latitude, across a habitat range from temperate grassland to tropical woodland and possibly forest (Zhu et al., 2003, Zhu et al., 2004 and Antn and Swisher, 2004). The oldest recorded hominin dispersal to East Asia apparently culminated in the ability to adapt to a wide variety of environments and, eventually, the lengthy persistence of H. erectus in East Asia prior to H. sapiens.

In that hypothesis, the cognitive adaptability of early Homo allowed humans to disperse into a diverse range of local ecologies. I think that both of these explanations capture some of the reality. Humans through most of the Pleistocene were successful as an edge species, making use of ecotones to increase the range of resources available to them at any given time. The reconstruction of the Yuanmou, Dmanisi, and Sangiran paleoenvironments have this aspect in common, and hominin assemblages in East Africa are largely consistent with this idea as well.

At any rate, I expect many more changes in the chronology of the Chinese archaeological record. There is a great story in the way that paleomagnetic chronologies have developed during the last decade, with an increasing ability to recognize very micro-scale periods of different polarity, which occasionally (as in the case of Malapa) allow very precise date estimates for archaeological or fossil assemblages.