Tag Archives: Anatomically modern human

Human evolution and revolution in Africa

Toba eruption: a hindrance or a spur to humans?

English: Erosional dissection of an ash deposi...

Ash-fall blanket at Mount Pinatubo volcano in the Philippines. (credit: Wikipedia)

The eruption that created the 100 by 30 km Toba caldera 74 ka ago was the largest recorded volcanic event during the two million years of the genus Homo’s evolution. It ejected an estimated 800 cubic kilometres of ash to blanket the land surface thousands of kilometres away. By analogy with the known effects of stratospheric ash and sulfate aerosols from  the much smaller 1991 eruption of the Mount Pinatubo in the Philippines, which  reduced mean global temperature by 0.5 °C, Toba might be expected to have had an even larger cooling effect, perhaps by as much as 10° C. Such a scenario has led palaeoanthropologists to suggest that there would have been major effects on humans migrating across Eurasia at the time, such as dramatic population reduction and maybe a genetic ‘bottleneck’ that could have led to rapid evolution among surviving generations. Yet, not only are stone tools found below the Toba Ash in Sumatra, but also in South India and immediately above it too. Yet analysis of Toba’s environmental effects recorded by sediments on the bed of Lake Malawi in southern African reveal little if any sign of a global ‘volcanic winter’.

A letter in Nature, published online on 15 March 2018 (Smith, E.J. and 15 others 2018. Humans thrived in South Africa through the Toba eruption about 74,000 years ago. Nature, v. 555; doi:10.1038/nature25967) decisively refutes any retardation of human cultural progress, in southern Africa at least, and suggests the opposite. Smith and colleagues from South Africa, Australia and the US found ash dated at around 74 ka 9,000 km away from Toba in sedimentary sequences that contain anatomically modern human remains and artefacts at the coastal Vleesbaai and Pinnacle Point sites in Cape Province South Africa. To check on the likelihood of a fortuitous coincidence of another eruption having shed the ash, the team compared detailed geochemical analyses of ash samples with those from other volcanoes and bona fide Toba samples, with a clear confirmation of provenance. In the archaeological record, rather than any sign of a cultural setback, the intensity of use of the sites increased after the ash-fall event, accompanied by significant technological innovations. Perhaps the Pinnacle Point community was lucky and also responded in the spirit of the adage ‘necessity is the mother of invention’. Discovery of the Toba ash at other ancient human sites would resolve the issue.

Hominin cultural revolution 320,000 years ago

As regards stone tools, the Olorgesailie Basin in southern Kenya is about as good as it gets; a long-used ‘factory’ that covers a time span from about 1. 2 to 0.03 Ma. In places, large areas of the surface underlain by sedimentary strata, some of which have become major tourist attractions, are liberally strewn with tools and debitage from their manufacture. The area is ideal for stone-tool makers: being within the East African Rift it contains outcrops of many hard, fine-grained volcanic rocks and cherts formed by hot springs interleaved with its dominant fill of lake and riverine sediments. There are two dominant sedimentary units: the Olorgesailie Formation (1.2 to 0.49 Ma) overlain by the Oltulelei  Formation (0.32 to 0.05 Ma), the time gap between the two marking an extended period of regional erosion. Despite the rich tool assemblages, hominin remains have yet to be unearthed from the sediments, although there are plenty of bones from potential prey mammals. Olorgesailie was  good place to live, especially as the Rift would have channelled migrating herds predictably between its steep-sided flanks.

Acheulean biface tools strewn on a bedding surface in the Olorgesailie Basin, Kenya (credit: mmercedes_78 https://www.flickr.com/photos/27325832@N06/3833105587)

The older formation has yielded biface tools of the Acheulean technology from bottom to top. The earliest Acheulean tools in Africa date back to about 1.7 Ma and have been attributed to Homo ergaster/erectus, although examples in Europe are associated with H. antecessor and H. heidelbergensis – the technology was active for about 1.4 Ma. The Acheulean method involved striking flakes from large blocks of rock to result in a symmetrical, pear-shaped core that served as a multipurpose tool.   The oldest strata in the Oltulelei  Formation contain exclusively tools that are very different , having been made by a significantly more complicated procedure and covering a wide variety of designs with different uses. This Levallois technique focused on thin flakes produced from cores after careful preparation, which enabled similar tools to be made repeatedly rather than relying on chance fracturing. Precise dating of the oldest of these assemblages gives an age of 320 ka (Deino, A.L. et al. 2018. Chronology of the Acheulean to Middle Stone Age* transition in eastern Africa. Science, v. 359 online; DOI: 10.1126/science.aao2216). The makers clearly were able to visualize the finished product within the original lump of raw stone, but in a more nuanced way than did the makers of Acheulean biface tools. The first-described Levallois tools were associated with European Neanderthals.

English: Levallois flake obtained by the prefe...

Producing a flake by the Levallois technique (credit: Wikipedia)

Sometime in the 500 to 320 ka interval removed by erosion a major shift in technology and almost certainly cognition took place. Not only was this a technological revolution, but the Levallois tools are found in association with a variety of pigments, such as ochres, which show signs of having been worked, presumably for decoration of some kind. Also, the tool makers seemed to have a clear preference for specific rocks – black, glassy obsidian and cherts of white and green hues from sources 25 to 90 km from the tool-making sites (Brooks, A.S. and 14 others 2018. Long-distance stone transport and pigment use in the earliest Middle Stone Age. Science, v. 359 online; DOI: 10.1126/science.aao2646). The sheer volume of tools at each site and the evidence for long-distance transport of the raw materials have prompted the authors to hazard a guess at some kind of trade, or at least cooperative intergroup interaction. Together with the use of pigment, probably for body ornamentation, this suggests individual and perhaps group identity within a kind of social network.

Of course, the big question is: Who made the leap? That’s a hard one in the absence of human remains associated with the tool-making factories at Olorgesailie . The authors of both papers argue for the earliest modern humans. But, to me, this seems like an assumption based on the age of the transition rather than any convincing evidence. The original Levallois tools from northern France were found in association with skeletal remains of Neanderthals but much later in the Pleistocene. An age of 320 ka does place the Olorgesailie tools in the same ballpark as early AMH fossils from Morocco, later than the genetically derived date of separation of Neanderthals and AMH. However, the 180 ka time gap in which the technological revolution took place gives some room for so-called African ‘archaic modern humans’ (not subdivided as are similar fossils from Europe) are known from Zimbabwe, Tanzania and Ethiopia. If the Neanderthals were using the Levallois technique in Europe there is every reason to suspect that they, or their possible forebears H. heidelbergensis, may have brought it with them from Africa.

The Olorgesailie tools figure in a third paper in the same volume of Science, but one with less shaky grounds (Potts, R. and 14 others 2018. Environmental dynamics during the onset of the Middle Stone Age in eastern Africa. Science, v. 359 online; DOI: 10.1126/science.aao2200). The wet-dry cycle of the Pleistocene, related to global warming and cooling in interglacial and glacial episodes respectively, had become more marked after the 500 to 320 ka period of tectonically induced erosion. In itself, this would have resulted in more marked shifts in the ecosystems of the basin – perhaps a case of necessity being the mother of invention. Yet, the evidence base for changing climate cycles in Africa is not from local lake-sediment stratigraphy, micropalaeontology or geochemistry, but from the modelled variation of insolation based on Milankovich’s hypothesis.

*Note:  The Middle Stone Age in Africa does not correlate with the Mesolithic of Europe, but is a legacy of the development of archaeology in Africa. It corresponds to the European Middle Palaeolithic.

See also:  Gibbons, A. Complex behaviour arose at dawn of humans. Science, v. 359, p. 1201-1202 (with video)

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Sophisticated Neanderthal art now established

The first detailed description and analysis of the amazing cave paintings of Western Europe that have been attributed to anatomically modern humans (AMH) were made in the early 20th century by the Jesuit priest Abbé Henri Breuil. As well as that those of Lascaux and Altamira, which have been dated, many works in Spanish caves have not. Art ascribed to AMH includes figurative work depicting a wide range of Late Pleistocene animals, abstract and perhaps symbolic designs, and ‘signatures’ of individual people in the form of direct prints or stencils of hands. The earliest known graphic work made by modern humans is a 100 ka-old baton of ochre with a zig-zag set of sharp incisions found with ochre-filled shells possibly for body painting at Blombos Cave in South Africa.

Evidence for pre-AMH work in Europe is sparse and widely  judged to be ambiguous; for instance 50 ka-old ochre-stained and pierced shells associated with Neanderthal remains in Spain.  Hints at even earlier origins for art lie in the geometrically etched bivalve shells excavated by Eugene Dubois at the site in Java where he discovered Homo erectus crania in 1891. They have recently been dated at around half a million years old.  Occasionally, radiometric dating of drawings has revealed quite meagre red dots that are slightly older than the widely accepted date of first entry of AMH into Europe (~40-45 ka) and may have been made by Neanderthals. Of course, there are many European cave paintings associated with dates earlier than the extinction of Neanderthals (around 30 ka) that may have been made by them, but which are generally ascribed to AMH by assuming that only our species has the wit to make them.  Even the sophisticated Châtelperronian stone tools and rough ornaments associated with undeniable Neanderthal remains are considered by many paleoanthropologists to show skills copied from AMH.

This AMH-centric view of art depends on two outlooks: simple prejudice that any beings markedly different in appearance from us were intellectually inferior – generally condemned as racist if applied to different groups of living humans; lack of incontrovertible and unambiguous evidence to the contrary. Both are set to be rigorously challenged by the growing use of sophisticated radiometric U-Th dating of the thin films of chemically precipitated calcite (flowstone or speleothem) that often coat the walls of caves and are at least as old as the art that they cover. A German-Spanish-British team has applied the technique to artwork and painted stalactites on the walls of three caves in Spain known to have been occupied by hominins over the last 100 ka (Hoffmann, D.L and 13 others 2018. U-Th dating of carbonate crusts reveals Neandertal origin of Iberian cave art. Science, v. 359, p. 912-915; doi: 10.1126/science.aap7778. See also: Appenzeller, T. 2018. Europe’s first artists were Neandertals. Science, v. 359, p.852-853; doi: 10.1126/science.359.6378.852). One cave that was analysed is that at La Pasiega in Cantabria whose art was sketched by Abbé Breuil. The team’s results are dramatic: all the dated samples pre-date 40 Ka, the oldest at 79.66±14.90 ka being from La Pasiega. Precisely dated art includes hand stencils, painted stalactites, geometric patterns and line drawings of animals. Many of the caves’ artworks remain to be dated, including some well-executed animals and strange, possibly symbolic designs.

Symbolic Neanderthal art in La Pasiega cave, Spain – left: recent photograph; right: sketch produced Abbé Breuil in 1913. The red, ladder-like symbol has a minimum age of 64 ka but it is unclear if the animals and other symbols were painted later. (credit: Hoffmann et al. 2018, Supplementary Data Figure S4)

The implications of this work are far-reaching. Handprints and stencils are common throughout the archives of European cave art and seem generally to be the oldest at each site. The dating method is yet to applied to the bulk of cave art, much of which is encased in speleothem, so it is quite possible that ‘dual authorship’ may be discovered in some caves. It now seems clear that Neanderthals invented permanent art independently of AMH, and since art is a form of communication that has implications for the ability to speak as well as to think ‘outside-the-box’. The 177 ka corral-like enclosures made of stalactites and associated hearths deep within Bruniquel Cave seem more likely to have ritual significance, far from the light of day, for the Neanderthals that made them. The finds throw doubt on the implausibility of Neanderthal invention of so-called ‘transitional’ technologies, such as the Châtelperronian. Finally, fully modern humans in Africa and Neanderthals in Europe were doing much the same things over roughly the same time period; genetically and physically they parted company about 450 to 400 ka ago; both were capable of artistic symbolism and fulfilled that potential. That implies that their common ancestor may have passed on the proclivity, as might their predecessor H. erectus who created the etched mollusc shells of Trinil half a million years ago.

More on Neanderthals, Denisovans and AMH genetic relatedness

Editorial from the Guardian Newspaper 26 February 2018.

Earliest departure of modern humans from Africa

In June 2017 the likely age of the earliest anatomically modern humans (AMH) was pushed back to almost 300 ka with the dating of their remains found at Jebel Irhoud in Morocco. It seemed only a matter of time before their first departure from Africa would also be shown to be earlier than generally believed at between 90 to 120 ka measured from AMH remains in the Skhul and Qafzeh caves of Israel. Such an exodus may be reflected by dates (80 to 113 ka) from fragmentary and indeterminate human remains in China, but a more definite, far-travelled AMH presence in east Asia is, so far, limited to about 60 ka. Yet there is genetic evidence from Neanderthal DNA from Germany and Siberia for human-Neanderthal interbreeding at some time between 219 and 460 thousand years before present: a very hazy intimation but one that needs accounting for. The main phase of genetic introgression from Neanderthals into Homo sapiens has been estimated to have occurred at between 50 to 60 ka; more easily explained by the known AMH peregrination into Asia in that period.

Misliya Cave on Mount Carmel, Israel has now added to the Levantine AMH record. A partial upper jaw and some teeth provide morphological data that fall within the range of H. sapiens fossils, along with tools ascribed to the Levallois technology. This involved striking flakes from a prepared core – a tortoise-like bulge on the flake that detaches when struck properly to form a pre-sharpened flake, flat on one side and rounded on the other. This method was shared by both AMH and Neanderthals, and examples of the tools extend as far back as 500 ka in Africa and may have been invented by a common ancestor of both human groups. Levallois tools were found with the AMH fossils at Jebel Irhoud and also in the Levant at Tabun, dated at 190 to 260 ka, but with no associated fossil remains of their makers. Those at Mislya Cave yielded a mean age from the use of three different dating methods at least 177 ka ago, making the fossil jaw found with them the earliest direct sign of AMH outside Africa (Hershkovitz, I. and 34 others 2018. The earliest modern humans outside Africa. Science, v. 359, p. 456-459; doi: 10.1126/science.aap8369).

So, Mislya supports the genetic evidence of human-Neanderthal Introgression in Eurasia (see; Stringer, C & Galway-Witham, J. 2018. When did modern humans leave Africa? Science, v. 359, p. 389-390; doi: 10.1126/science.aas8954) and provides a spur to extend work in China and between Arabia and eastern Asia. For decades the anatomically modern human remains in the Levant have been sidelined, that near-Mediterranean area being widely regarded as a ‘boulevard of broken dreams’. That is, until Levalloisian tools dated at up to 125 ka were found in the United Arab Emirates and Arabia as a whole had been shown to have had a monsoonal climate during the glacial period that preceded the last, Eemian interglacial and in several later episodes. Once in the Levant, and provided they continually had a foothold there, AMH had many windows of opportunity to move further east without having to await falls in sea-level to open routes such as that across the Red Sea via Straits of Bab el Mandab.

Neanderthal development

Despite the lingering public image that Neanderthals were not as bright as fully modern humans some had significantly larger brains than we do, albeit with most of the difference being in the rear part of the brain region. So they may have had different powers, such as enhanced vision and awareness of position (proprioception). Because there are few cranial fossils of immature Neanderthals and, for them, little evidence of ages, not much is known about how they developed from birth. A common assumption has been that because their brain was larger post-natal development much have been faster than in modern humans. Set against our slow post-natal development and the faster pace in chimpanzees this assumption has been used in support of limited Neanderthal cognitive abilities.

The El Sidron Neanderthal boy, including a reconstruction of his skull and brain cast. (credit: Antonio Rosas, Museo Nacional de Ciencias Naturales, Madrid, Spain)

The El Sidron cave in Asturias region of northern Spain has yielded fossil remains of a dozen Neanderthals dated at between 49 and 37 ka, the time when anatomically modern humans were also present in Europe. They are among the best studied examples of this human group. Three were of boys, the best preserved of whom is estimated to have died at 7.7 years old from analysis of his dental development (Rosas, A. and 10 others 2017. The growth pattern of Neandertals, reconstructed from a juvenile skeleton from El Sidrón (Spain). Science, v. 357, p. 1282-1287; doi:10.1126/science.aan6463) Analysis of signs of the maturation stage that he had reached, including that of his brain, show no fundamental difference from modern human juveniles in his overall pace of growth. Other workers have found that a similarly aged Homo erectus boy from Kenya had indeed developed more quickly than modern human juveniles.

It’s not much to go on, but the El Sidron boy supports the view that Neanderthals were not much different from us.

You can find more information on migration of modern humans here.

Early modern humans in Sumatra before the Toba eruption

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.

Neanderthal culture confirmed

The Châtelperronian material culture represents the earliest sign of the Upper Palaeolithic in Europe and its products span a period from about 45 to 40 ka. It includes stone tools, such as points and long, thin blades with a single cutting edge and a blunt back, reminiscent of a modern knife, and others with notched, or denticulate edges that resemble saw blades. A great many of the tools, including ivory and bone ones, are probably designed for working and stitching skins. But the most revealing worked objects are animal teeth, shells and fossils that are either bored or grooved to be strung together. The best have been found in the Grotte du Renne in eastern France. The most controversial aspect of the Châtelperronian is that its artefacts are sometimes found with the fossil remains of Neanderthals who had previously produced less sophisticated, Mousterian tools since around 160 ka. The controversy centres on whether or not Neanderthals created the Châtelperronian culture, and if so, did they develop them independently or through cultural exchange with or copying from the newly arrived anatomically modern humans (AMH).

Science Magazine

Châtelperronian ornaments from the Grotte du Renne eastern France, probably parts of a necklace. (Credit: ©Marian Vanhaeren, CNRS, University of Bordeaux)

The Grotte du Renne material is especially rich in ornaments, but insufficient fossil material is present to tell from anatomical characteristics whether or not they were made by AMH or Neanderthals. It has now become possible using traces of bone proteins to detect hominin bone fragments and DNA to assess which group is implicated (Welker, F. and 127 others, 2016. Palaeoproteomic evidence identifies archaic hominins associated with the Châtelperronian at the Grotte du Renne. Proceedings of the National Academy of Science, www.pnas.org/cgi/doi/10.1073/pnas.1605834113). Analyses of mtDNA and radiometric dating of the bones that yielded it show that the Grotte du Renne tools and ornaments link with Neanderthals who lived there about 37 ka ago. Interestingly, the stratigraphic horizon beneath the definite Neanderthal occupation level contains their earlier, Mousterian artefacts. So it seems that they developed new manufacturing techniques and material culture. Yet, the findings do not resolve the issue of independent invention or copying AMH methodology.

Importantly, Grotte du Renne shows that Neanderthals, even if they copied AMH techniques, were capable of appreciating, producing and using personal ornamentation: they could learn and transmit ideas. In that respect, here is support for the notion that, apart from significant anatomical differences from AMH they were not that different intellectually.

More on Neanderthals, Denisovans and anatomically modern humans

Wade, L. 2016. Neandertals made jewelry, proteins confirm. Science, v. 353, p. 1350.