Category Archives: Anthropology and Geoarchaeology

Neanderthal demographics and their extinction

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About 39 thousand years ago all sign of the presence of Neanderthal bands in their extensive range across western Eurasia disappears.Their demise occurred during a period of relative warmth (Marine-Isotope Stage-3) following a cold period at its worst around 65 ka (MIS-4). They had previously thrived since their first appearance in Eurasia at about 250 ka, surviving at least two full glacial cycles. Their demise occurred around 5 thousand years after they were joined in western Eurasia by anatomically modern humans (AMH). During their long period of habitation they had adapted well to a range of climatic zones from woodland to tundra. During their overlap both groups shared much the same food resources, dominated by large herbivores whose numbers burgeoned during the warm period, with the difference that Neanderthals seemed to have depended on ranges centred on fixed sites of habitation while AMH maintained a nomadic lifestyle. Having shared a common African ancestry about 400 thousand years ago, DNA studies  have revealed that the two populations interbred regularly, probably in the earlier period of overlap in west Asia from around 120 thousand years ago and possibly in Europe too after 44 ka. Considering their previous tenacity, how the Neanderthals met their end is something of a mystery. It may have been a result of competition for resources with AMH, which could be countered by the increase in food resources. Maybe physical conflict was involved, or perhaps disease imported with AMH from warmer climes. Genetic absorption through interbreeding of a small population with a larger one of AMH is a possibility, although DNA evidence is lacking. An inability to adapt to climate change contradicts the Neanderthals long record and their disappearance during MIS-3. Previous population estimates of changing Neanderthal populations in the Iberian Peninsula (see Fig. 2 in Roberts, M.F. & Bricher, S.E 2018. Modeling the disappearance of the Neanderthals using principles of population dynamics and ecology. Journal of Archaeological Science, v. 100, p.16-31; DOI: 10.1016/j.jas.2018.09.012) show decline from about 70,000 to 20,000 before MIS-4, then recovery to about 40,000 before the arrival of AMH at 44 ka followed by a decline to extinction thereafter. Roberts and Bricher developed a model for investigating demographics from archaeological evidence that is neutral as regards any particular hypothesis for Neanderthal extinction.

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Artistic reconstruction of Neanderthal family group (credit: Nikola Solic, Reuters)

Attempting to take modelling further, another research consortium from France has focussed on the demographic changes needed to draw Neanderthals to extinction (Degioanni, A. et al. 2019. Living on the edge: Was demographic weakness the cause of Neanderthal demise? PLOS One, v. 14(5): e0216742; DOI: 10.1371/journal.pone.0216742). It is based on studies of living hunter-gatherer groups and those from the recent past. Survival of individuals in such groups is strongly age-dependent, i.e. low survival among juveniles, high among individuals in their prime and decreasing among the elderly. Fertility also varies among females, increasing from post-pubescence to ages between 21 to 30 years. In groups that practice sexual pairing between individuals from different communities (exogamy) migration from one to another is necessary to avoid inbreeding. The modellers assumed that only individuals from 16 to 18 years old migrated in this way. They found that a small decrease (~8%) in the fertility rate of younger females (<20 years) having a child for the first time could produce the decreasing trend in Neanderthal populations during the 5,000 year period of sharing resources with AMH populations. This would have culminated in the extinction of the Neanderthals, irrespective of the fertility rates of older, pre-menopausal females. So what could trigger such a change from a primiparous fertility rate that gave stable or growing population to one that ended so badly? The authors make no suggestion, eschewing the ‘why’ for the ‘how’. All they suggest is that the decrease in Neanderthals, which would have benefited AMH settlement in the vacated areas, could have occurred without any need for some catastrophic event, such as disease, slaughter or climate change. Any of these causes would probably have resulted in more rapid extinction. However, the lead author, Anna Degioanni from Aix Marseille Université, when interviewed by The Independentnewspaper said. ‘First-time pregnancies, especially in young females (less than 20 years old), are on average more at risk than second and other pregnancies… a slight decrease in food may explain a reduction in fertility, especially among first-time mothers’.

One of the key features of Neanderthals is that they were probably sedentary with widely spaced communities across their huge range. So exogamy would have been more difficult for them than it would have been for nomadic groups. Genetic evidence from a few Neanderthals suggests that inbreeding was an issue. Had it been widespread among Neanderthals – risky to infer from such scanty information – that may also account for decreased primiparous fertility and also survival of newborns.

Related article: Neanderthals may have died out because of infertility, new model suggests. (The Independent)

Denisovan on top of the world

Who the Denisovans were is almost completely bound up with their DNA. Until 2019 their only tangible remains were from a single Siberian cave and amounted to a finger bone, a toe bone three molars and fragment of limb bone. Yet they provided DNA from four individuals who lived in Denis the Hermit’s cave from 30 to more than 100 thousand years ago. The analyses revealed that the Denisovans, like the Neanderthals, left their genetic mark in modern people who live outside of Africa, specifically native people of Melanesia and Australia . Remarkably, one of them revealed that a 90 ka female Denisovan was the offspring of a Denisovan father and  a Neanderthal mother whose DNA suggested that she may have come from the far-off Balkans. Living, native Tibetans, whose DNA has been analysed, share a gene (EPAS1) with Denisovans, which regulates the body’s production of haemoglobin and enables Tibetans and Nepalese Sherpas to thrive at extremely high altitudes (see The earliest humans in Tibet).

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Baishya Karst Cave in eastern Tibet with Buddhist prayer flags (Credit: Dongju Zhang, Lanzhou University)

Part of a hominin lower jaw unearthed by a Buddhist monk in 1980 from a cave on the Tibetan Plateau, at a height of 3280 m, found its way by a circuitous route to the Max Planck Institute for Evolutionary Anthropology in Leipzig in 2016. It carries two very large molars comparable in size with those found at the Denisova Cave, and which peculiarly have three roots rather than the four in the jaws of non-Asian, living humans’. East Asians commonly show this trait. This and other aspects of the fossil teeth resemble those of some uncategorised early hominin fossils from China. Dating of speleothem calcium carbonate with which the jaw is encrusted suggests that the fossil dates back to at least 160 thousand years ago, around the oldest date recovered from Denisova Cave; during the glacial period before the last one. So the individual was able to survive winter conditions worse than those experienced today on the Tibetan Plateau. Further excavation in the cave found numerous stone artefacts and cut-marked animal bones (Chen, F. and 18 others 2019. A late Middle Pleistocene Denisovan mandible from the Tibetan Plateau. Nature, v. 569, published online; DOI: 10.1038/s41586-019-1139-x).

Unfortunately the Tibetan Jaw did not yield DNA capable of being sequenced, so the issues of inheritance of the ‘high-altitude’ gene and wider relatedness of the individual could not be checked. However, one of the teeth did contain preserved protein that can be analysed in an analogous way to DNA, but with less revealing detail. The results were sufficient to demonstrate that the mandible was consistent with a hominin population closely related to the Denisovans of the Siberian cave.

No doubt a path has already been beaten to the Tibetan cave, in the hope of further hominin material. To me the resemblance of the Tibetan fossil jaw to other hominin finds in China, including those from Xuchang, summarised here, is exciting. None of them have been subject to modern biological analysis. Perhaps the ‘real Denisovan’ will emerge from them.

See also: Mysterious ancient human found on the ‘roof of the world’ (National Geographic magazine); Major discovery suggests Denisovans lived in Tibet 160,000 years ago (New Scientist) ; Finally, a Denisovan specimen from somewhere beyond Denisova Cave (Ars Technica)

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‘Hobbits’ found in the Philippines

The earliest signs that hominins had colonised the island of Luzon in the Philippines took the form of crude stone tools found around half a century ago. Re-excavation of one of the sites uncovered yet more tools buried in a river-channel deposit, along with remains of a butchered rhinoceros dated at around 700 ka by two methods (see Clear signs of a hominin presence on the Philippines at around 700 ka May 2018). The primitive nature of the tools and their age suggested that Asian Homo erectus had managed to reach the Philippine archipelago, despite it being separated from larger islands by deep water.  Even during large falls in sea level (up to 130 m) during glacial periods that exposed Sundaland, which linked the larger islands of Indonesia to mainland Eurasia, at best only a narrow stretch of sea (~20 km) connected the Philippines to the wider world. For most of the time since the earliest known colonisation any hominins on the islands would have been cut off from other populations.

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Topography of the Philippines, showing location of the Kalinga site. Palest blue sea may have been above sea level only during extreme glacial maxima. (credit: Wikipedia)

The first hominin fossil found by archaeologists in 2007 was a 67 ka old toe bone (metatarsal) in cave sediments from Northern Luzon. It was undoubtedly from Homo, but which species was unclear.  More recent excavations added a mere 12 fossil fragments, probably from three individuals; 7 teeth, 4 adult finger- and toe bones and part of the femur of a juvenile (Détroit, F. and 8 others 2019. A new species of Homo from the Late Pleistocene of the Philippines. Nature, v.  568, p. 181–186; DOI: 10.1038/s41586-019-1067-9). The finger bones, being curved, are unlike those of modern humans and H. erectus. The teeth are even more different; for instance the premolars show two or three roots – ours have but one – and their unusually tiny molars only a single root. The combined features are sufficiently distinct to suggest a separate species (H. luzonensis). The small teeth may indicate that the adults may have been even smaller that the ‘Hobbits’ of Flores and anatomically different.

Like H. floresiensis, as a result of isolation the new human species probably evolved to become small, possibly from very low number of H. erectus original colonisers. But an even stranger possibility is suggested by their curved toe and finger bones. They may have been habitual climbers as much as walkers – unlike us and H. erectus. Could that indicate that their ancestors left Africa already distinct from the rest of Late Pleistocene humans? That is also a disputed hypothesis for the origins of H. floresiensis  remains of whom are more complete. Similarly, they pose the issue of how their progenitors managed to get to the archipelago: deliberately by boat or being carried there clinging in desperation to vegetation torn-up by tsunamis and transported seawards by the back-wash.

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A stratigraphic timeline for the Denisova Cave

Denisova Cave was named to commemorate an 18th century hermit called Denis, who used it as his refuge. The culmination of more than four decades of excavation, which followed the discovery there of Mousterian and Levallois tools there, has been the explosion onto the palaeoanthropological scene of Denisovan genomics, beginning in 2010 with sequenced DNA from a child’s finger bone. The same layer yielded Neanderthal DNA from a toe bone in 2013. Another layer yielded similar evidence in 2018 of an individual who had a Neanderthal father and a Denisovan mother. Application of the new technique of peptide mass fingerprinting, or zooarchaeology by mass spectrometry (ZooMS), to small, unidentifiable bone fragments from the cave sediments revealed further signs of Denisovan occupation and the first trace of anatomically modern humans (AMH). So far the tally is 4 Denisovans (two female children and two adult males), a Neanderthal woman and the astonishing hybrid. Analyses of the sediments themselves showed traces of both Neanderthal and Denisovan mtDNA from deeper in the stratigraphy than levels in which human fossils had been found, but which contained artefacts. The discovery of the first Denisovan DNA revealed that AMH migrants from Africa who reached the West Pacific islands about 65 ka ago carried fragments of that genome. As well as hybridising with Neanderthals some of the people who left Africa had interbred with Denisovans sufficiently often for genetic traces to have survived. Yet, until now, the ages of the analysed samples from the cave remained unknown.

That is no surprise for two reasons: cave sediments are complex, having been reworked over millennia to scramble their true stratigraphy; most of the organic remains defied 14C dating, being older than its maximum limit of determination. However, using alternative approaches has resulted in two papers in the latest issue of Nature. The first reports results from two methods that rely on the luminescence of grains of quartz and feldspar when stimulated, which measures the time since they were last exposed to light (Jacobs, Z. and 10 others 2019. Timing of archaic hominin occupation of Denisova Cave in southern Siberia. Nature, v. 565, p. 594-599; DOI: 0.1038/s41586-018-0843-2). Over 280 thousand grains in 103 sediment samples from different depths and various parts of the cave system have yielded a range of ages from 300 to 20 ka that span 3 glacial-interglacial cycles except for a few gaps, giving rough estimates of the timing of hominin occupation shown by fossils and soil layers that contain DNA. The youngest evidence for Denisovans is shown to be roughly 50 ka; a time when AMH was present elsewhere in Siberia. They lived at a time halfway between the 130 ka interglacial and the last glacial maximum. Two Neanderthals, a Denisovan and the hybrid occupied the site during the 130 ka interglacial. Soils from the previous warm episode from 250 to 200 ka contain both Neanderthal and Denisovan DNA traces. The oldest occupancy, marked by the presence of a Denisovan bone sample, was 300 ka ago, once again midway between an interglacial and a glacial maximum.

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All the hominin remains found in Denisova Cave: Note the common scale. (Credit: Douka et al. 2019; extended data Figure 1)

The second paper (Douka, K. and 21 others 2019. Age estimates for hominin fossils and the onset of the Upper Palaeolithic at Denisova Cave. Nature, v. 565, p. 640–644; DOI: 10.1038/s41586-018-0870-z) focused on direct dating of the hominin fossils themselves – and thus their DNA content, important in trying to piece together timings of genetic mixing. In the absence of radiocarbon dates from the bones themselves because of most specimens’ >50 ka ages, except in the case of the youngest whose 14C age is at the 50 ka limit. They resorted to a hybrid technique based on a means of modelling fossils’ ages from differences in mtDNA between the specimens and that in the youngest hominin, which, luckily, was dateable by radiocarbon means. Weighted by dating of the actual sediments that contain them, the differences should become greater for successively older fossils because of random mutations: a variant of the ‘molecular clock’ approach. It’s complicated and depends on assuming that mitochondrial mutation rate was the same as that in modern humans. Unsurprisingly the results are imprecise, but sufficient to match the hominin fossil occurrences with different environmental conditions

Pollen grains and vertebrate fossils from various levels in the cave system demonstrate the wide climatic and ecological conditions in which the various hominins lived. The warmest episodes supported broad-leafed forest, offering maximum resources for hominin survival. Those between interglacial and full glacial conditions were much less benign, with alternating dry and wet cold conditions that supported open steppe ecosystems. The oldest Denisovan occupation was at the close of a period of moderately warm and humid conditions that supported mixed conifer and broad-leafed trees that gave way to reduced tree cover.

As well as the presence of stone tools sporadically through the sedimentary sequence, in the youngest levels there are bone rings and pendants made from deer teeth; clearly ornamental items.  Did the late Denisovans make them or do they signify anatomically modern human activity? Radiocarbon ages do not give a concrete answer, one of the pendants is about 45 ka old with an error that puts it just within the range of age variation of the oldest Denisovan fossil. No AMH remains have been found in Denisova Cave, but remains of a modern human male have been found at Ust’-Ishim, in NW Siberia. At 45 ka, he represents the earliest arrival of AMH in northern Asia. So it may have been members of this new population that left ornaments in Denisova, but, for the moment, artistic Denisovans are a possibility.

Further deployment of rapid screening for hominin bone fragments using the ZooMS method and analyses for traces of DNA in soils is likely to expand the geographic and time ranges of Denisovans and other close human relatives. Denisova Cave formed in Silurian limestones of the Altai Range, and there are other caves in those hills …

Related article: Dennel, R. 2019. Dating of hominin discoveries at Denisova. Nature, v. 565, p. 571-572; DOI: 10.1038/d41586-019-00264-0)

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Early stone tools spread more widely

The rift systems of Ethiopia, Kenya and Tanzania, and the limestone caverns near Johannesburg, South Africa have a long history of intensive archaeological study, rewarded by many finds of hominin skeletal remains and artifacts over the last century. Each region lays claim to be the birthplace of humans, that in South Africa being grandiloquently dubbed ‘The Cradle of Humankind’. Of course, the realistic chances of making discoveries and careers draws scientists and funds back to these regions again and again: a kind of self-fulfilling prophesy fueled by the old miners’ adage, ‘to find elephants you must go to elephant country’. The key site for the earliest stone tools was for a long time Tanzania’s Olduvai Gorge, thanks to finds of deliberately shaped choppers, hammer stones and sharp edges from about 2 Ma ago in close association with remains of Homo habilis by the Leakeys. Termed ‘Oldowan’, signs of this industry emerged from 2.6 Ma sediments in the Afar Depression of Ethiopia in 2010, but with no sign of who had made them. By 2015 the cachet of ‘first tools’ moved to Lomekwi on the shore of Lake Turkana in Kenya, dated to 3.3 Ma but again with no evidence for a maker. In fact the oldest evidence for the use of tools emerged with the 2010controversial discovery at Dikika in Afar of 3.4 Ma old bones that carry cut marks, but no sign of tools nor whoever had used them. However remains of Australopithecus afarensis occur only a few kilometers away.

Excavations outside the East African Rift System and South Africa are still few and far between, especially from before 1 Ma. The High Plateaus of eastern Algeria include one ancient site, near Ain Hanech, which yielded 1.8 Ma Oldowan stone artifacts as long ago as 1992. A nearby site at Ain Boucherit takes the North African record back to 2.4 Ma with both Oldowan tools and cut-marked bones of horse and antelope (Sahnouni, M. and 12 others 2018. 1.9-million- and 2.4-million-year-old artifacts and stone tool–cutmarked bones of from Ain Boucherit, Algeria. Science, v. 362, p. 1297-1301; DOI: 10.1126/science.aau0008). Tool makers had clearly diffused across what is now the Sahara Desert by that time. Given the distance between the Lomekwi and Dikika sites in East Africa that is hardly a surprise, provided climatic conditions were favourable. Michel Brunet’s discovery in 3.3 Ma old sediments of an australopithecine (Au. bahrelghazali) in central Chad demonstrates that early hominins were quite capable of spreading across the African continent. Yet, to wean palaeoanthropologists and their sponsors from hitherto fruitful, ‘elephant’ areas to a more ‘blue skies’ approach is likely to be difficult. There are plenty of sedimentary basins in Africa that preserve Miocene to Recent sediments that may yet turn up fossils and artifacts that take the science of human origins and peregrinations further and possibly in unexpected taxonomic directions

Related article: Gibbons, A. 2018. Strongest evidence of early humans butchering animals discovered in North Africa. Science News online; doi:10.1126/science.aaw2245.

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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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More early art from South Africa?

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Silcrete flake from Blombos with crosshatching drawn in red ochre. (Credit: C. Foster)

The Blombos Cave 300 km east of Cape Town is where the earliest signs of art produced by anatomically modern humans were found (see Snippets on human evolution October 2011). The most publicized was a shaped piece of ochre etched with a hashed pattern of lines (Henshilwood, C.S. et al. 2018. An abstract drawing from the 73,000-year-old levels at Blombos Cave, South Africa. Nature v. 561, online; DOI: 10.1038/s41586-018-0514-3). This and the ochre-processing workshop where it was found gave a date of about 100 ka, Now another item has hit the newsrooms; a  ground piece of flinty silcrete that shows signs of being the product of knapping, on which has been drawn a similar pattern, which resembles the now ubiquitous ‘hashtag’ associated with Twitter. The level in the excavation from which it was removed gives an age of about 75 ka. Like the earlier artifact, it involved the use of ochre but in a way that has been said to be an example of drawing or painting, rather than etching. It is likely to have been produced by a sharpened piece of solid ochre, perhaps a kind of crayon

For some reason the object has been hyped as the earliest example of art and of advanced cognitive abilities. But the pattern is not as complex as that on the original etched ochre block from Blombos, or even those on a freshwater mussel from Trinil in Java that could have =been made by associated Homo erectus between 430 and 500 ka ago. This does not take the context at Blombos into account. There is ample evidence that ochre, along with charcoal and burnt seal bone, was being ground there and made into paint found in an abalone shell. It can be surmised that such paint was used for some kind of decoration that has not yet been discovered. That is quite possibly because it was used for body paint as similar materials are still widely used.  Now anyone – male or female – who uses cosmetics today, be it foundation, lipstick, eye-liner and -shadow or the truly fabulous make-up used by the Kathakali performers of Kerala, takes an age to try and to decide on which of an almost imperceptible range of shades to apply. Ochres are like that, as any native Australian artist will tell you.

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Lord Rama face paint in Kathakali

To me, the most likely origins of both kinds of Palaeolithic hashtag are: in the case of the ‘drawing’, checking the colour and ‘grindability’ of a sharpened piece of red ochre before use; and for the etched block, using a sharp tool to grind off small amounts from what may have been a well-used block of an especially valued hue.

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

Neanderthal Mum meets Denisovan Dad

Two bone fragments from the Denisova Cave – the former abode of an 18th century Russian hermit called Denis – in the Altai region of Siberia yielded ancient  DNA. One matches that from previously analysed Neanderthal remains and the other a genome that could only be ascribed to a hitherto unknown ancient-human population, now known as the Denisovans. Since their discovery further analysis of both modern and ancient DNA has shown that modern humans living outside of Africa contain a few percent of DNA from both ancient-human groups. Soon after leaving Africa some of their ancestors interbred with both; indeed a 40 ka-old modern-human jaw from Romania revealed genetic evidence that the individual had a Neanderthal great-great grandparent. Their descendants spread far and wide to populate Eurasia, Australasia and the Americas. Using the ancient DNA to peer back in time suggests that Neanderthals and Denisovans diverged from a common ancestor between 470 and 380 ka, itself having split from modern-human ancestry between 770 to 550 ka. Denisovan DNA also contains evidence that its ancestry included segments that could only have come from a totally unknown hominin species. Interestingly, DNA from the Neanderthal bone fragment found at Denisova contains fragments from an anatomically modern-human.

Tourists at the entrance to Denisova Cave, Rus...

Tourists at the entrance to Denisova Cave, Russia (credit: Wikipedia)

With such riches from tiny fragments of human bones unearthed from the Denisova Cave, it is no surprise that the team led by Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has subsequently analysed others that showed signs of human proteins. The latest ‘takes the biscuit’. A fragment of limb bone from someone who was at least 13 years old yielded DNA commensurate with their having been the child of a Neanderthal mother and a Denisovan father (Slon, V. and 18 others 2018. The genome of the offspring of a Neanderthal mother and a Denisovan father. Nature, v. 560, published on-line; doi: 10.1038/s41586-018-0455-x). Their child was a girl, who has been nicknamed ‘Denny’ by the team, though ‘Denise’ might seem more appropriate. The only clues to what her father, or any Denisovan, might have looked like stem from a few teeth and a skull fragment from the cave that have yielded Denisovan DNA. The teeth are much larger and the skull fragment is thicker than those of Neanderthals, suggesting that Denisovans were distinctly bigger and more robust than even the sturdy Neanderthals.

The father came from a population related to a later Denisovan found in the cave – the first to be sequenced. This suggests long-term occupancy of the area by Denisovans. But his genome also carries traces of Neanderthal ancestry. Surprisingly, the mother is more closely related to Croatian Neanderthals, rather than to an earlier Neanderthal found in the cave. Neanderthals were clearly capable of migrating between Europe and eastern Eurasia; more than 5000 km in this case. Even though very few archaic humans have been genetically sequenced it is beginning to look as if genetic mixing between diverse hominin groups in the last half million years was common, when they actually met. A custom of marrying outside a closely related group (exogamy) has been popular throughout recorded history; indeed it makes sound genetic sense. With the tiny human population density during the Late Pleistocene, it may then have been cause for mutual celebration.  As documented in Chapters 2 and 3 of David Reich’s Who We Are and How We Got Here (Oxford University Press, 2018) human origins since about 470 ka until the present chart a history of episodic migrations and genetic mixing that certainly makes nonsense of earlier ideas of ‘racial purity’ and casts doubt even on the term ‘species’ as regards members of the genus Homo.

If we are ever to discover who the Denisovans were and what they looked like, the evidence is likely to come from East Asia at latitudes where climate favours preservation of DNA. Advanced sequencing equipment and techniques are now operational in China, where suspected Denisovan remains have been found

See also: Warren, M. 2018. First ancient-human hybrid. Nature, v. 560, p. 417-418; doi: 10.1038/d41586-018-06004-0); Sample, I. 2018. Offspring of Neanderthal and Denisovan identified for first time. The Guardian (22 August 2918).

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

Multiregional human evolution in Africa

Africa is not only a large continent, but is subdivided into many different climatic zones and ecosystems and these have changed drastically over the last 2 Ma. It is further subdivided by terrain features, such as the courses of major rivers, large plateaus, tectonic rift systems and the mountains that frequently define their flanks. Getting around Africa is not easy today, was more difficult before modern transport, and many geomorphic provinces may have been mutually inaccessible in the distant past. For instance, the Sahara Desert forms a major barrier to travellers on foot because access to surface water is non-existent except at widely spaced oases. Without boats or rafts the Nile and Congo cannot be crossed for a thousand miles or more. Migration was perhaps a very rare event outside of periods of widespread humid climates or when great environmental stress forced people either to move or perish. Despite these physical and ecological divisions and barriers palaeoanthropologists have, until recently, tended to regard the evolution of Homo sapiens and earlier human and hominin species as having occurred within single populations: a linear view forced on them by scanty fossil remains and limited methodologies. Logically, when human numbers were small Africa probably had several isolated population Physical isolation would have engendered genetic isolation in which our ancestors evolved for tens of thousand years.

Anatomically modern human (AMH) remains found at Jebel Irhoud in Morocco turned out to be 315 ka old, displacing those from Ethiopia (190 ka) as the earliest known examples of AMH. Several more archaic H. sapiens fossils have turned up in southern Africa and as far afield as the Middle East, suggesting that the early evolution of AMH was in an Africa-wide context rather than in one area – the rift system of Ethiopia and Kenya – from which a new species radiated outwards. This breadth of finds has encouraged Eleanor Scerri of Oxford University and her many international colleagues to resurrect what was once a widely discarded hypothesis; a multiregional model of modern human origins, originally proposed to have arisen from pre-sapiens groups in Eurasia by Milford Wolpoff but which was sunk once genetic connections among living humans turned out to be rooted in Africa. (Scerri, E.M.L. and 22 others 2018. Did our species evolve in subdivided populations across Africa, and why does it matter? Trends in Ecology & Evolution, v. 33, p. 582-594; (PDF) doi: 10.1016/j.tree.2018.05.005). Scerri et al’s model is sited in Africa and the paper’s authors include several leading palaeoanthropologists who once opposed multiregionalism and established the Recent African Origin hypothesis on the back of the early genetic data.

early homo

Different early AMH cranium shapes: left Jebel Irhoud, Morocco (315 ka), right Qafzeh, the Levant (85 ka) (credit: Scerri et al, 2018; Figure 1)

From region to region in Africa, the oldest AMH crania show significant differences from each other, but within a distinct combination of features that clearly distinguish us from our fossil relatives and ancestors, such as Homo heidelbergensis from Zimbabwe and the primitive-looking H. naledi found in a South African cave in 2015. Improved dating now shows that the Zimbabwean H. heidelbergensis and H.naledi remains are roughly the same age as the Jebel Irhoud AMH specimens. The first has long been held as the progenitor of AMH and descended from H. antecessor, perhaps the common ancestor for AMH, Neanderthals and Denisovans about 700 ka ago. The three human species cohabited Africa early in the evolutionary history of AMH. It is now abundantly clear from ancient and modern genomes that AMH, Neanderthals and Denisovans interbred in Eurasia. The proximity in time and space of earlier African AMH to two more ancient human species opens up a similar possibility earlier in the emergence of all living humans. There is evidence for that too: Yoruba people living in West Africa, whose genomes have been analysed, carry up to 8% of genetic ancestry that originated in an unidentified ancient population that was non-sapiens. At present, DNA analysis with the same high precision and information content from other living Africans has not been performed, and deterioration of ancient DNA in African climates has so far thwarted genomic studies of ancient African fossils.

The new view of our origins points to repeated hybridisation involving other coexisting human species, as well as evolution in isolation, from the outset. It continued through later times while Neanderthals and Denisovans survived. Even recent human genetic history is peppered with intermingling of a great variety of migrants passing through all the habitable continents. Another issue: In the earliest times, were cultures exchanged as well as genes? The first appearance of AMH coincides with that of a new stone technology (Levallois technique), moving away from the earlier dominance by handaxes towards more delicate, leaf-shaped points, that characterise the African Middle Stone Age. Similar techniques reached Europe with the Neanderthals. Was this an invention of the earliest AMH or a joint venture?

You can find an excellent review of these issues in the September 2018 issue of Scientific American (Wong, K. 2018. Last hominin standing.  Scientific American, v. 319(3), p. 56-61) along with several other articles on human evolution.

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

The hobbits of Flores: An update

Homo floresiensis (the "Hobbit")

Homo floresiensis from Liang Bua Cave, Flores, Indonesia. (Credit: Wikipedia)

In October 2004 the world’s news media headlined the discovery of fossil remains of a tiny adult human on the Indonesian island of Flores, dated at around 18 ka. At only 1 m tall, with a brain cavity around a third the size of ours, yet having used stone tools and fire she was a sensational find. Someone so tiny and with such a small brain seemed highly unlikely to some palaeoanthropologists. Others claimed she was of a different species altogether. Homo floresiensis was also challenged as a new species and attributed to some congenital cause of small stature in a modern human – H. sapiens had first colonised Flores between 50 and 35 ka. But the subsequent discovery of remains of nine more individuals revealed skeletal details that were definitely un-human, with a suggestion of greater affinity to H. erectus. Her stature even suggested to a few anthropologists that she may have descended from migrant H. habilis, previously known only from 2 Ma ago in East Africa. The issue of relatedness was partly resolved by further dating of the cave strata that entombed the ‘hobbit’ which pushed her back to between 190 to 50 ka, beyond the earliest date of modern human colonisation. Further fragmentary fossil finds in more easily dated sediments on Flores showed the earliest known H. floresiensis lived around 700 ka ago. Stone tools and butchered prey remains on the island go back to 1 Ma, when the hominin trail goes cold.

English: Cave where the remainings of ' where ...

Liang Bua cave where the remains of Homo floresiensis were discovered in 2003. (credit: Wikipedia)

A plausible theory for these human’s ‘hobbit’-like size is an evolutionary process known as island dwarfism, akin to that which produced the tiny elephants (Stegodon) on which they preyed. Such dramatic size reduction may arise through the influence of stringently limited food resources on the evolution of descendants from a restricted founder population, genetically cut-off from larger, more widespread populations. It now appears that such dwarfism has also affected a modern human population living on Flores (Tucci, S and 14 others 2018. Evolutionary history and adaptation of a human pygmy population of Flores Island, Indonesia. Science,  v. 361, p. 511-516; doi: 10.1126/science.aar8486). A group of people of diminished stature live within shouting distance of the Liang Bua cave in which Homo floresiensis was first discovered. On average adults in the village are about 1.45 m tall. They certainly are not relict H. floresiensis, just significantly smaller than other Indonesian people living on Flores.

Serena Tucci and colleagues analysed the DNA of 32  adult pygmies from the village of Rampasasa. They show no sign of DNA from any other archaic human population than the Neanderthal and Denisovan traces that every living person outside of Africa carries – the pygmies are not descendants of H. floresiensis and are little different from other Indonesians and the rest of us. The analysis does show, however, that their ancestors carried a mixture of DNA from East Asia and New Guinea; perhaps a result of several waves of migration between 50 and 5 ka. They also carry significantly more DNA segments that are linked to short stature than do other East Asians. This suggests natural selection favored existing genes for shortness while the pygmies’ ancestors were on Flores; in other words they display an example of island dwarfism akin to that probably explaining the ‘hobbits’. Moreover, the people of Rampasasa show signs of an evolutionary adaptation to an almost exclusively meat and seafood diet, possibly arising after they migrated to Flores and had to depend on the available fauna but little in the way of plant foods.

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