Tag: Early human migration

The earliest humans to leave Africa, in China

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Since discovery in 2010 that remains of the genus Homo at Dmanisi in Georgia were about 1.85 Ma old several more instances of bones and stone tools a few hundred thousand years less than that age have turned up in China. All have been ascribed to H. erectus, although there are dissimilarities with African examples of the species and its predecessor H. ergaster. The technological breakthrough that led H. erectus/ergaster to knap the distinctive bifacial or Acheulean ‘handaxe’ was achieved at about the same time as the Dmanisi humans left Africa, yet there is no sign of such tools in eastern Asia until much later, most ancient artefacts there being of a more primitive, ‘Oldowan’ type. That is perhaps because more serviceable tools were fashioned from less durable materials than fine-grained rock that takes an edge. Maybe the skills were lost en route or the forebears of eastern Asian tool makers left Africa before the breakthrough. At any rate, the genus Homo is generally conferred on any being that had a tool-making culture, so that the presence of tools alone in a sedimentary deposit signifies that humans probably once inhabited that site. The earliest tools (3.3 Ma) from the Turkana area of Kenya were made half a million years before the first known appearance of well-documented remains of an un-named member of the genus Homo at  Ledi-Geraru in Afar, Ethiopia (2.8 Ma). At sites in Olduvai, Tanzania (1.9 Ma) and Turkana, Kenya (2.1 Ma) fossils of Homo habilis are found in association with ‘Oldovan’ stone tools.

Sites where early human fossils an tools have been found. (Credit: John Kappelman, Nature 2018; doi:10.1038/d41586-018-05293-9)

The latest development in the origin and wanderings of early humans has emerged from studies of a thick deposit of windblown silt or loess that makes up the Loess Plateau (Latitude 34°N) between the Yellow and Yangtze Rivers in central-east China. The loess is divided into several sequences by thin soil horizons (palaeosols). The entire stratigraphy contains tiny grains of iron minerals whose magnetic polarity was aligned with the Earth’s magnetic field at the time of deposition. This allows periods of normal and reversed geomagnetic polarity to be detected with considerable precision. Measurements have been taken at 10 cm intervals throughout the loess, to give an unbroken record of events throughout the Pleistocene Epoch that can be matched to a dated reference called the geomagnetic polarity timescale (GPTS). Palaeoclimate researchers have been able to show that the layers of loess correspond to successive glacial stages, whereas the palaeosol represent warm interglacials, exactly as recorded in sea-floor sediment profiles   A team of archaeologists from China and Britain have found primitive, Oldowan-type, artefacts in both the loess and palaeosol horizons at 17 different levels (Zhu, Z. and 10 others 2018. Hominin occupation of the Chinese Loess Plateau since about 2.1 million years ago. Nature, v. 559 advance publication online doi:10.1038/s41586-018-0299-4. See also). The artefacts are positioned at levels dated at between 1.26 to 2.12 Ma by the palaeomagnetic dating (from the Réunion to Cobb Mountain normally polarized subchrons).

Primitive stone tool (four sides shown) from the Loess Plateau of China. (Credit: Zhu et al./Nature 2018)

So, in both cool and warm conditions (34°N has cold winters today) toolmakers were regularly present in central, east China for almost 900 ka. The earliest must have made a 14 thousand km trek from tropical Africa across several climatic zones, and been physically, cognitively and technologically capable of surviving and reproducing for the one- to three-thousand years the journey must have taken (based on a dispersal rate of 5 to 15 km a year estimated from modern hunter-gatherers’ activities). Either there were repeated migrations of this scale or a pioneer population survived on or within reach of the loess steppe for hundreds of thousand years. The earliest emigrants would have been neither Homo erectus nor ergaster, for neither had evolved. Their age suggests that they may have been H. habilis, a view that has been expressed for the ancestors of the diminutive H. floresiensis known to have been present of the Indonesian island of Flores for around 700 ka. Until actual fossils are unearthed – not easy as the sequence is exposed in very steep slopes characteristic of dissected loess terrains – who the first occupants of China were remains mysterious. But one thing stands out: If early humans from that long ago could arrive, survive and prosper half a world away from their place of origin, then paleoanthropologists must consider the possibility of continual diffusion of the genus Homo away from its African origins once equipped with the ability to make tools. China may become the focus for early-human research as it became for that into the origins of birds and feathered dinosaurs.

You can read more about early humans and their evolution here.

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

Clear signs of a hominin presence on the Philippines at around 700 ka

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For over half a century the presence of crude stone tools on several SE Asian islands, such as Flores and Sulawesi in Indonesia and Luzon in the Philippines, have hinted at their colonisation by Asian Homo erectus. Hominin fossils have yet to be exhumed, outside of Flores (Homo floresiensis) and dating the earlier finds has been imprecise, but evidence continues to accumulate. As regards the Philippines, the earliest hominin fossil is a modern human toe bone dated at 66.7 ka. Another curious feature of these isolated parts of what might be termed  ’Wallacea’, on broader floral and faunal grounds, is the presence in the Pleistocene fossil record of large mammals, or at least dwarfed species of megafauna found in mainland Asia. These include elephants, rhinos and deer.

Topography of the Philippines, showing location of the Kalinga site. Palest blue sea would have been above sea level during glacial maxima. At such times Borneo would have been part of Sundaland – linked to mainland Asia (credit: Wikipedia)

A large team, with members from France, Philippines, Australia, Spain, Germany, Holland, Spain and Greece, has been excavating a tool- and fossil-rich site in thick alluvium at Kalinga in northern Luzon since 2014 (Ingicco, T. and 22 others 2018. Earliest known hominin activity in the Philippines by 709 thousand years ago. Nature, published online). It occurs in an erosional channel filled with mud. Stone artefacts comprise 56 flakes, hammer stone and cores, the tools being crude – a common feature of the Asian H. erectus lithic culture, unlike that in Africa and Europe. As well as fragments of other animals, the site is notable for a 75% complete, but disarticulated, skeleton of a rhinoceros scattered over a small area. That in itself suggests that the beast may have been butchered, and is confirmed by cut marks and signs of smashing on several of the bones. Uranium-thorium dating of one of the animal’s teeth (709±68 ka) and sediment grains from above and below the fossiliferous unit by electron-spin resonance (701±70 and 727±30 ka respectively) confirms the great antiquity of the site. Dating of volcanic plagioclase crystals from sediments by the 40Ar/39Ar method yields even older dates around 1 Ma, but the crystals may have been washed for older volcanic ash deposits.

It seems beyond doubt that early hominins, possibly H. erectus, colonised Luzon some 700 ka ago, yet, according to the authors, ‘it still seems too farfetched to suggest that H. erectus, or another unknown Pleistocene ancestral candidate … were able to construct some sort of simple watercraft and deliberately cross sea barriers’. That seems to be pushing caution a little too far. Do the authors not believe their own – to me compelling – evidence and analyses? But the paper spent a year in review, so maybe they came up against a singularly pernickety referee (three are named but one remains anonymous). Presumably, if a hominin fossil turns up during on-going excavations, that would change everything apart from the question, ‘Did they walk, swim or navigate?’ Luzon and the Philippines archipelago as a whole are surrounded by sea shallow enough for them to have been a single landmass during a glacial maximum when sea level was around 100 m lower than at present. At such a juncture a less than 20 km sea journey would have separated the Philippines from Borneo, then part of a vast area of lowland to the SW (Sundaland) that was connected to the Asian mainland.

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

Early modern humans in Sumatra before the Toba eruption

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In late July 2017 news emerged that modern humans first reached Australia at least 65 thousand years ago. Confirming that the date of departure from Africa to end up in SE Asia and Australasia was  considerable earlier than previously believed, deposits in Sumatra that contain remains of early Home sapiens have yielded even older ages (Westaway, K.E. and 22 others 2017. An early modern human presence in Sumatra 73,000–63,000 years ago. Nature v. 548 online; doi:10.1038/nature23452). This resulted from a re-examination of material from the Padang Caves first excavated more than a century ago by Eugène Dubois, famous for his discovery in Java of the first H. erectus remains. A richly fossiliferous breccia in the Lida Ajer cave yielded a fauna characteristic of a rainforest biome and included two teeth that Dubois considered to be human. Several later palaeontologists confirmed his identification as have hominin specialists in the present Australian-Indonesian-American-British-Dutch-German team. The fossil assemblage has long suggested great antiquity for the site, but only now has it been dated precisely. The dating employed three methods: optically stimulated luminescence dating of quartz grains from the breccia (85±25 to 62±5  ka); uranium-series dating of speleothem including fragments of hollow ‘soda-straw’ stalactites(84±1 to 71±7 ka); uranium-series dating of gibbon and orangutan teeth found together with the human teeth (86±13 to 76±7 ka). Statistical analysis of the age data suggests 73 to 63 ka for the fauna, with a maximum age for deposition of the breccia of 84±1 ka.

Satellite image of Lake Toba, the site of a VE...
Satellite image of Lake Toba in NW Sumatra (at centre), the site of the largest volcanic eruption during the history of human evolution ~71,600 years ago (credit: Wikipedia)

Stone tools which may have been carried by anatomically modern humans into the area have previously been used to suggest a minimum date of the arrival of migrants, though they may have been carried by ­H. erectus. Remarkably, such tools have been found beneath a thick bed of volcanic ash found throughout southern Asia and in Indian Ocean sediment cores. This has been dated at 71.6 ka and represents the explosive collapse of the caldera now containing Lake Toba in NW Sumatra that was the largest volcanic event in the entire history of the genus Homo. The new age data from Lida Ajer suggests that modern humans were present in its vicinty before the eruption, a view also supported by ‘molecular-clock’ dating of the range of mitochondrial DNA carried by living SE Asian people (79 to 75 ka). So, despite the stupendous magnitude of the Toba eruption is seems likely that some of the migrants survived.  Together with the dating of the earliest Australians the Sumatran evidence is at odds with the view, widely held by palaeoanthropologists, that the ‘Out of Africa’ exodus began by crossing the Straits of Bab el Mandab between 74 and 58 ka when global sea-level fell markedly during marine oxygen-isotope Stage 4 (MIS4). A problem with that hypothesis has been that climatic and ecological conditions in southern Asia during MIS4 were unfavourable. But is seems that modern humans were already there and capable of adapting to both the climate shift and to the devastation undoubtedly caused by Toba.

Surprising modern-human migrations into China and Africa

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Caves figure highly in discoveries of hominin remains, fossil riches from those near Johannesburg in South Africa and at Atapuerca in northern Spain having set the world of palaeoanthropology reeling in the last few months. As often as not the caves chosen by hominins for day-to-day living, refuge or ritual, places where carnivores dragged some of our early relatives, or into which they fell accidentally, formed in limestones. There are few places so well endowed with karst features than southern China, a fair number of caves in them having rich deposits of bat guano to which farmers have beaten well-trodden paths to dig it out for fertiliser. One such is Fuyan Cave in Daoxian County, Hunan. Manure mining there had done a great deal of the heavy work faced by archaeologists, having stopped when it reached a hard layer of calcite speleothem or flowstone that underpaves more or less the entire cave floor. Initial trial investigations found three clearly human teeth at the surface, encouraging further work. Digging through the flowstone revealed sediments rich in fossils, mainly teeth which preserve better than other remains in humid conditions. As well as teeth from a variety of mammals, large and small, 47 human teeth emerged. Close study revealed dental features that are irrefutably those of anatomically modern humans (Liu, W. and 13 others 2015. The earliest unequivocally modern humans in southern China. Nature, doi:10.1038/nature15696). Remarkably, many of the teeth are in far better condition than my own, and those of many living people with access to dental expertise.

Some of the Daoxian human teeth. (Credit: Song Xing and Xiu-jie Wu of the 1Key Laboratory of Vertebrate Evolution and Human Origins at the Chinese Academy of Sciences
Some of the Daoxian human teeth. (Credit: Song Xing and Xiu-jie Wu of the 1Key Laboratory of Vertebrate Evolution and Human Origins at the Chinese Academy of Sciences)

The true significance of the excavation emerged only when 230Th dating revealed the age of the flowstone cap to the old cave sediments. A small stalagmite protruding from its surface yielded a minimum age of ~80 ka: by far the oldest date for anatomically modern human remains outside of Africa and the eastern Mediterranean. The dating produced older ages around 120 ka with equally good precision. Before this discovery the date of migration of Africans to populate Eurasia was thought to be about 60 ka from imprecise dating based on genetics of a range of living Eurasians and Africans – a ‘molecular clock’ – and the earliest sign of humans found in Australia. Consequently, finds in South India of artefacts beneath 74 ka ash from the super-eruption of the Mount Toba caldera have been regarded by many, other than the finders, as having been made by Homo erectus. Dates of 100 ka for modern human occupation of the Levant were thought to represent a failed attempt at migration out of Africa by a northern route. Both these important findings now take on renewed significance. Yet a 30 to 40 ka time gap between the Fuyan people and the previous dates for the earliest signs of migration into China, Borneo and Australia (40-50 ka) begs the question, ‘Did this early group of far-travelled migrants survive to become ancestors of modern Chinese people?’ There are many possible scenarios that only future discoveries might validate: simply goiung extinct; failure to survive the encounter with earlier migrants, such as H. erectus or the Denisovans; assimilation into those older populations.

Mitochondrial DNA-based chart of large human m...
Mitochondrial DNA-based chart of large human migrations: the consensus before these new data. Numbers are millennia before present. ( credit: Wikipedia)

As if to counter this, a multinational group of collaborators have sequenced and analysed the genome from a 4500 year-old male skeleton discovered in the Mota Cave of the Gamo highlands of southern Ethiopia (Llorente, M.G. and 18 others 2015. Ancient Ethiopian genome reveals extensive Eurasian admixture throughout the African continent. Science, DOI: 10.1126/science.aad2879). Comparison with what is now a virtual library of living human genomes showed that this man’s genetic make-up most closely matched that of the Ari, a tribe living in the area today. What was most interesting is that part of the modern Ari genome – between 4 to 7% – is not present in the 4500 year-old sequence. Instead, it matches those of modern Sardinians and a prehistoric German farmer. Yet it occurs in people living not only in Ethiopia, but also in central, western and southern Africa to varying degrees. There seems to have been a ‘backflow’ of people into the whole of Africa from Eurasia, estimated to have occurred some 3500-4000 years ago and probably involving a large influx. By that time farming was already established in Africa, so the migrants may have had some advantage, either culturally or physically, to encourage their wide spread through the continent.

In tropical climates, DNA is likely to break down quickly and little if any fossil DNA has been recovered from prehistoric Africans. In this case, burial in a cave at high elevation may have helped preserve it, but also the target for extraction was the petrous bone from the inner ear whose density seems to allow DNA a better change of long-term survival. With continually improving DNA analysis and sequencing techniques more news is surely going to emerge from past African populations.

More on human migrations

Related articles

Gibbons, A. 2015. Prehistoric Eurasians streamed into Africa, genome shows. Science, v. 350 (9 October 2015), p. 149.

Hominin updates

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A new approach to 14C dating at the Oxford Radiocarbon Accelerator Unit at the University of Oxford UK, combined with detailed analysis of human teeth to distinguish fully modern human remains from those of Neanderthals has pushed back the date and pace of migration into Europe by people whose tools define the Aurignacian and Italian Uluzzian technologies. These are the earliest modern-human cultures found in Europe, but some of the tools are similar to those produced by Neanderthals (Châtelperronian culture), raising the possibility of transfer of technologies between the two groups. So, without confirmation from human remains of the anatomical affinities the would be doubts about using tools of these kinds to signify the presence at a site of full modern humans. Teeth found decades ago at caves in SW England and southern Italy prove, on detailed comparative study, to be from ‘moderns’ (Higham, T. And 12 others 2011. The earliest evidence for anatomically modern humans in northwestern Europe. Nature, v. 479, p. 521-524; Benazzi, S. And 13others 2011. Early dispersal of modern humans in Europe and implications for Neanderthal behaviour. Nature, v. 479, p. 525-528).The new carbon-isotope method  efficiently eliminates chemical contamination of material by post-fossilisation processes and so tend to increase the measured age of samples. The two studies produced exciting results: dates of occupation between 42-43 and 43-45 ka from SW England and southern Italy respectively. Together with results from other sites throughout central and southern Europe, the discovery shows that widespread colonisation was accomplished in three to five thousand years by migrants probably from the Levant, who may have travelled along three routes fanning out from the Bosporus in modern Turkey: along the Danube; along the Adriatic coast; from southern Greece to the ‘heel’ of Italy.

In early 2011 a group of archaeologists led by Simon Armitage of the University of Birmingham, UK reported stone tools from a cave in the United Arab Emirates for which they derived possible ages of 125, 95 and 40 ka (see Human migration in EPN for January 2011). The older dates were coeval with anatomically modern humans in the Levant, but the tools themselves showed features that could not be matched decisively with those from any other sites, including those in the Leant, though they most resembled collections from East and NE Africa. Armitage and colleagues suggested that the people who occupied the UAE cave had crossed the Red Sea at the time of the glacial maximum around 130 ka, at a time of unprecedented low sea level. A recent paper adds considerable weight to this idea (Rose, J.I. and 9 others 2011. The Nubian Complex of Dhofar, Oman: An African Middle Stone Age Industry in Southern Arabia at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028239). Jeffrey Rose, also of the University of Birmingham, and colleagues from Ukraine, US, UK, Germany, the Czech Republic and Australia excavated site in Dhofar southern Oman, much closer to the Straits of Bab el Mandab than the UAE. Chert tools found in the area are of the Levallois type, specifically resembling closely those found widely in the Nile Valley of southern Egypt and northern Sudan, and in the Afar Depression of Ethiopia, in deposits dated between 128 to 74 ka. The Omani tools yielded an optically stimulated luminescence age of about 106 ka. This nicely confirms that Africans had moved far beyond the confines of their home continent by the last interglacial episode, with the route to South Asia open to them along the shores of the Persian Gulf and Indian Ocean. However, the route that they had taken could equally have been around the head of the Red Sea as across the Bab el Mandab.