Out of Africa: The earliest modern human to leave

The 2017 discovery in Morocco of fossilised, anatomically modern humans (AMH) dated at 286 ka (see: Origin of anatomically modern humans, June 2017) pushed back the origin of our species by at least 100 ka. Indeed, the same site yielded flint tools around 315 ka old. Aside from indicating our antiquity, the Jebel Irhoud discovery expanded the time span during which AMH might have wandered into Eurasia, as a whole variety of earlier hominins had managed since about 1.8 Ma ago. Sure enough, the widely accepted earliest modern human migrants from Skhul and Qafzeh caves in Israel (90 to 120 ka) were superseded in 2018 by AMH fossils at Misliya Cave, also in Israel, in association with 177 ka stone artefacts (see Earliest departure of modern humans from Africa, January 2018). Such early dates helped make more sense of very old ages for unaccompanied stone tools in the Arabian Peninsula as tracers for early migration routes. Unlike today, Arabia was a fertile place during a series of monsoon-related cycles extending back to about 160 ka (see: Arabia : staging post for human migrations? September 2014; Wet spells in Arabia and human migration, March 2015). The ‘record’ has now shifted to Greece.

hominin sites
Key ages of early H. sapiens, Neanderthals and Denisovans (credit: Delson, 2019; Fig. 1)

Fossil human remains unearthed decades ago often undergo revised assessment as more precise dating methods and anatomical ideas become available. Such is the case for two partial human skulls found in the Apidima Cave complex of southern Greece during the late 1970s. Now, using the uranium-series method, one has been dated at 170 ka, the other being at least 210 ka old (Harvati, K. and 11 others 2019. Apidima Cave fossils provide earliest evidence of Homo sapiens in Eurasia. Nature, v. 571 online; DOI: 10.1038/s41586-019-1376-z). These are well within the age range of European Neanderthals. Indeed, the younger one does have the characteristic Neanderthal brow ridges and elongated shape. Albeit damaged, the older skull is more rounded and lacks the Neanderthals’ ‘bun’-like bulge at the back; it is an early member of Homo sapiens. In fact 170 ka older than any other early European AMH, and a clear contemporary of the long-lived Neanderthal population of Eurasia; in fact the age relations could indicate that Neanderthals replaced these early AMH migrants.

Given suitable climatic conditions in the Levant and Arabia, those areas are the closest to Africa to which they are linked by an ‘easy’, overland route. To reach Greece is not only a longer haul from the Red Sea isthmus but involves the significant barrier of the Dardanelles strait, or it requires navigation across the Mediterranean Sea. Such is the ‘specky’ occurrence of hominin fossils in both space and time that a new geographic outlier such as Apidima doesn’t help much in understanding how migration happened. Until – and if – DNA can be extracted it is impossible to tell if AMH-Neanderthal hybridisation occurred at such an early date and if the 210 ka population in Greece vanished without a trace or left a sign in the genomics of living humans. Yet, both time and place being so unexpected, the discovery raises optimism of further discoveries to come

See also: Delson, E. 2019. An early modern human outside Africa. Nature, v. 571 online; DOI: 10.1038/d41586-019-02075-9

The earliest humans in Tibet

Modern Tibetans thrive in the rarefied air at altitudes above 4 km partly because they benefit from a genetic mutation of the gene EPAS1, which regulates haemoglobin production. Surprisingly, the segment of Tibetan’s DNA that contains the mutation matches that present in the genome of an undated Denisovan girl’s finger bone found in the eponymous Siberian cave. The geneticists who made this discovery were able to estimate that Tibetans inherited the entire segment sometime in the last 40 thousand years through interbreeding with Denisovans, who probably were able to live at high altitude too. Wherever and whenever this took place the inheritance was retained because it clearly helped those who carried it to thrive in Tibet. The same segment is present in a few percent of living Han Chinese people, which suggests their ancestors and those of the Tibetans were members of the same group some 40 ka ago, most of the Han having lost the mutation subsequently.

That inheritance would have remained somewhat mysterious while the existing evidence for the colonisation of the Tibetan Plateau suggested sometime in the Holocene, possibly by migrating early farmers. A single archaeological site at 4600 m on the Plateau has changed all that (Zhang, X.L. and 15 others 2018. The earliest human occupation of the high-altitude Tibetan Plateau 40 thousand to 30 thousand years ago. Science, v.  362, p. 1049-1051; DOI: 10.1126/science.aat8824). The dig at Nwya Devu, which lies 250 km NW of Lhasa, has yielded a sequence of sediments (dated by optically stimulated luminescence at between 45 to 18 thousand years) that contains abundant stone tools made from locally occurring slate. The oldest coincides roughly with the age of the earliest anatomically modern human migrants into northern China, so the earliest Tibetans may well have been a branch of that same group of people, as suggested by the DNA of modern Tibetan and Han people. However, skeletal remains of both humans and their prey animals are yet to emerge from Nwya Devu, which leaves open the question of who they were. Anatomically modern humans or archaic humans, such as Denisovans?

The tools do not help to identify their likely makers. Slate is easy to work and typically yields flat blades with sharp, albeit not especially durable, edges; they are disposable perhaps explaining why so many were found at Nwya Devu. None show signs of pressure flaking that typify tools made from harder, more isotropic rock, such as flint. Yet they include a variety of use-types: scrapers; awls; burins and choppers as well as blades. The lack of associated remains of prey or hearths is suggested by the authors to signify that the site was a workshop; perhaps that will change with further excavation in the area. The age range suggests regular, if not permanent, occupancy for more than 20 ka

Related articles: Gibbons, A. 2014. Tibetans inherited high-altitude gene from ancient human. Science News,2 July 2014, Zhang J-F. & Dennell, R. 2018. The last of Asia conquered by Homo sapiens. Science, v. 362, p. 992-993; DOI: 10.1126/science.aav6863.

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