Life with the Neanderthals

From Robinson Crusoe’s discovery of Friday’s footprint on his desert island to Mary Leakey’s unearthing of a 3.6 Ma old trackway left by two adults and a juvenile of the hominin species Australopithecus afarensis at Laetoli in Tanzania, such tangible signs of another related creature have fostered an eerie thrill in whoever witnesses them. Other ancient examples have turned up, such as the signs of mud trampled by 800 ka humans (H. antecessor?) at Happisburgh, Norfolk, UK (see Traces of the most ancient Britons, February 2014). From a purely scientific standpoint, footprints provide key evidence of foot anatomy, gait, travel speed, height, weight, and the number of individuals who contributed to a trackway. At Le Rozel on the Cherbourg Peninsula in Normandy, France – about 30 km west of the D-Day landing site at Utah beach – Yves Roupin, an amateur archaeologist, discovered a footprint on the foreshore in the 1960s close to the base of a thick sequence of late-Pleistocene dune sediments exposed below a rocky cliff. Fifty years later, rapid onset of wind and tidal erosion threatened to destroy the site, so excavations and scientific analysis began. This involved excavation of thick overburden on an annual basis to expose as much of five footprint-bearing horizons as possible (about 90 m2).

Le Rozel
The Le Rozel excavation, with weighted plastic sheets to protect the site from erosion between visits (credit: Dominique Cliquet)

More and more prints emerged, each photographed and modelled in 3-D, with the best being preserved as casts using a flexible material, similar to that used by dentists (Duveau, J. eyt al. 2019. The composition of a Neandertal social group revealed by the hominin footprints at Le Rozel (Normandy, France). Proceedings of the National Academy of Sciences. 9 September 2019; DOI: 10.1073/pnas.1901789116). At the end of the excavation hundreds of prints had been found and recorded. They had been preserved in wet sand, probably deposited in an interdune pond. Luminescence dating of sand grains revealed that the footprints were produced around 80 ka ago, 35 ka before Europe was occupied by anatomically modern humans. Scattered around the site are numerous fossils of butchered prey animals, together with stone tools typical of Neanderthal technology.

Such a large number of footprints presented a unique opportunity to analyse the social structure of the Neanderthal group that produced them, for they came in many different sizes. During the very short period in which they were produced and buried by wind-blown sand, an estimated 10 to 13 individuals had crossed and re-crossed the site – there may have been more individuals who didn’t happen to cross the wet patch But the evidence suggests that children and adolescents, one of whom may have been as young as 2 years, predominated. Two or three with the biggest feet were probably adults as tall as 1.9 metres – about 20 cm taller that the average for modern human males. That is surprising for Neanderthals who are widely believed to have been more stocky. The fact that footprints occur in 5 horizons suggests that the band, or perhaps family, found the site to be good for occupation. Wider hypotheses are a little shaky. Did Neanderthals have large families? Does the predominance of children and adolescents indicate that they died young? But perhaps children stayed close to habitations with just a few ‘minders’, while other adults went off hunting and foraging. Were the kids playing?

Australopithecus anamensis; a face to fit the name

Ethiopian palaeoanthropologist Yohannes Haile-Selassie of the Cleveland Museum of Natural History, Ohio, USA has been involved in the search for early human ancestors in the Awash Valley of the Afar Depression in Ethiopia since 1990. The Middle Awash Project, founded by his mentor Tim White, has been enormously successful over the years. That is because most members from the top down are persistent, inured to heat and sharp sighted. Haile-Selassie is a case in point. In 2016 near a place called Miro Dora, he and a local worker independently spotted two parts of what turned out to be a near-complete cranium of an australopithecine (Au. anamensis) (Haile-Selassie, Y. et al. 2019. A 3.8-million-year-old hominin cranium from Woranso-Mille, Ethiopia. Nature, v. 572, published online; DOI: 10.1038/s41586-019-1513-8). When it was dated at about 3.8 Ma, using the 40Ar/39Ar method and magnetic reversal stratigraphy (Saylor, B.Z. and 13 others 2019. Age and context of mid-Pliocene hominin cranium from Woranso-Mille, Ethiopia. Nature, v. 572, published online; DOI: 10.1038/s41586-019-1514-7), his find caused quite a stir.

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The near-complete cranium of an Au. anamensis found in the Afar Depression of NE Ethiopia. Note the lateral fflattening caused by sedimentary burial. (Credit: Cleveland Museum of Natural History)

Fragmentary hominin fossils, including a complete lower jaw, found near Lake Turkana, Kenya in 1994 were sufficiently different from other, known australopithecines to warrant their recognition as a new species, Australopithecus anamensis. Seeming more ape-like than the famous ‘Lucy’ fossil Au. afarensis and also older – 3.9 to 4.2 Ma compared with 3.0 to 3.8 Ma for Lucy’s species –  Au anamensis  has long been regarded as a possible ancestor of afarensis, or even a more primitive member if the same species. The new, almost perfect cranium – except for some distortion during burial – cohabited the Afar Depression with Au. afarensis, for as long as 100 ka, and is sufficiently different to retain its species status. Because many palaeoanthropologists consider Au. afarensis to be early in the evolutionary line that lead to humans, the new find seems to throw a spanner in this linear hypothesis. However, there is another possibility that may resolve the issue.

During the Pliocene, Afar was a very diverse place with many volcanoes, lava flows and minor rift systems. It is possible that geographic complexity separated and isolated small groups allowing them to diverge genetically, in the manner of island faunas. Australopithecus afarensis may have arisen from such isolation, going on to outcompete its ‘parent’ species Au anamensis whose numbers progressively dwindled. Nevertheless, the emerging diversity of coexisting hominin populations in the Pliocene seriously challenges linear evolutionary hypotheses aimed at understanding the origin of our own genus (see Taking stock of hominid evolution February 2002 and Hominid evolution: a line or a bush? May 2006).

See also: Video of the discovery and summary of subsequent research

Barras, C. 2019. Rare 3.8-million-year-old skull recasts origins of iconic ‘Lucy’ fossil. Nature, v. 572, p. ; DOI: 10.1038/d41586-019-02573-w

Spoor, F. 2019. Elusive cranium of early hominin found. Nature, v. 572, p. ; DOI: 10.1038/d41586-019-02520-9

 

Symbolic art made by Denisovans (?)

The deep soil by a permanent spring in a vegetable allotment on the edge of the small town of Lingjing near Xuchang City in Henan Province, China has provided a wealth of stone artefacts and bone fragments to a depth of 10 m (see Denisovan(?) remains in the garden, March 2017). Optically stimulated luminescence (OSL) dating of mineral grains shows that the last time that the deepest soils were exposed to sunlight was between 78 to 123 ka. Long before the first arrival of anatomically modern humans (AMH) in China the site had been much as it is today, a human habitation site. Among the bones were fragments of the crania from five human individuals, perhaps either Homo erectus descended from the earliest arrivals in China or more recent Denisovans closely related to the Neanderthals of western Eurasia. Reconstruction of the two most complete crania hinted at the second possibility by resemblance to Neanderthal anatomy yet the complete lack of evidence that Neanderthals travelled so far to the east.

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Top: lines etched through ochre veneer on a rib bone from Lingjing, China; bottom: hashed lines carved on a faceted block of hematite from Blombos Cave (Credit: Li et al 2019; Fig. 3 and Chris Henshilwood)

So far there have been no reports of DNA from these enigmatic fossils, but some of the bones from the deepest layers show etched, roughly parallel lines (Li, Z et al. 2019. Engraved bones from the archaic hominin site of Lingjing, Henan Province. Antiquity, v. 370, p. 886-900; DOI: 10.15184/aqy.2019.81). Analysis shows that they were deliberately made after the bones had been defleshed: the fragments have thin veneers of red ochre through which the deep scratches reveal white bone. They are not cut marks, but the scratches on previously reddened bone suggest some form of design. This is by no means the earliest symbolic art, for shells associated with Eugene Dubois’s ~500 ka old ‘Pithecanthropus’ (Homo) erectus remains from Trinil, Java are similarly engraved (see Art from half a million years ago. December 2014). Yet the Lingjing engravings predate the oldest know symbolic art from the Blombos Cave of South Africa that was produced by AMH who lived in about 75 ka ago. Neanderthal artistic ability has shown up at many sites (see Human evolution and migrations, March 2011; May 2016; February 2018)

An ability to express mental concepts of some kind in a durable way now seems to have characterised at least four human species over the last half-million years.

See also: Schuster, R. 2019. Prehistoric Art or Doodle? 110,000-year-old Engraved Bones Create New Mystery (Haaretz, 31 July 2019); Denisovan(?) remains in a Chinese garden (Earth-logs, March 2017)

Humans gorged on giant mole rats during Ethiopian glaciation

Until recently it was believed that humans only adapted to life at high elevations, such as those of the Tibetan Plateau, during the Holocene. Then it turned out that the DNA of modern Tibetans contains a mutated gene (EPAS1) that boosts haemoglobin production that underpins their comfortably living at above 4000 m. In quick succession it was discovered that modern humans were living in Tibet as early as 30 to 40 ka, the same gene was found in Denisovan DNA and then a jawbone of that earlier human emerged from a Tibetan cave. It has been estimated that ancestral Tibetans inherited the DNA segment from Denisovans at around 40 ka. The ancestral African homeland of our genus Homo has large highland tracts that rise above 4000 m, most notably Mount Kilimanjaro (5895 m, Tanzania), Mount Kenya (5199 m Kenya) and Mount Stanley (5109 m, Rwenzori, Uganda). Those three retain glaciers, albeit small ones. But during the last glacial maximum permanent ice fields also capped highland areas in Morocco, Ethiopia and South Africa. Today there are permanent or seasonal habitations above 4000 m in all these African settings because of warmer conditions, but DNA analyses of the inhabitants have yet to be tested for the EPAS1 genetic mutation.

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Glacial erratic in the Bale Mountains National Park, Ethiopia (credit: James Steamer)

Understandably, research into the former glaciation of highland areas in tropical Africa is a hot topic. One of the largest areas of glacial till and moraine in Africa lies on the >4000 m high Sanetti Plateau in the Bale Mountains of south-eastern Ethiopia. These mountains are the dissected remnants of a Miocene shield volcano and host a rich ecosystem; in fact the largest reserve of Afro-alpine flora and fauna. Like many mountains in tropical Africa, Bale helps rising moist air to condense as mists. The resulting rich ecology makes such mountain systems high-elevation ‘oases’ surrounded by semi-arid to arid savannah and desert. Because this was likely to have been equally true during the more arid conditions of the last glacial period areas such as Bale may have been refuges for humans during those times, despite the risk of altitude sickness (hypoxia). Aarchaeologist Götz Ossendorf of the University of Cologne, together with a large team from Germany, France, Ethiopia, Switzerland the USA, set out to test this hypothesis ( Ossendorf, G. and 21 others 2019. Middle Stone Age foragers resided in high elevations of the glaciated Bale Mountains, Ethiopia. Science, v. 365, p. 583–587; DOI: 10.1126/science.aaw8942).

Their main target was to excavate a rock shelter at around 3500 m, but outcrops of volcanic glass (obsidian) at 4200 m had clearly attracted human interest  as they are scattered with flaked tools and debitage from their manufacture. The upper sediment layers in the rock shelter yielded ashes, charcoal, a few pottery shards and a glass bead, together with evidence for herbivore droppings. Dates fall in the last 800 years; hardly surprising as the Bale Plateau is seasonally visited by local herders who use rock shelters as corrals for livestock. The lower levels, however, contain artefacts of the Middle Stone Age (MSA); the African terminology roughly equivalent to the Upper Palaeolithic in Eurasia. The MSA layer also contain coprolites, some of hyena in its upper parts but also massive amounts likely to be human that extend to the base of the cave sediments. Dated at 47 to 31 ka, the sediments bracket the age of maximum glacier extent.

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Alert giant mole rat in Ethiopia’s Bale Mountains (credit: M. Watson)

The lower cave sediments contain abundant animal bones and signs of several hearths. Some of the bones show signs of cooking from burn marks. Although several prey species occur, more than 90% of the bones are those of giant mole rats (Tachyoryctes macrocephalus). It is not difficult to conclude that the human population’s meat consumption was almost entirely of roasted mole rat. That is not surprising because the thin soils of the Bale Mountains support at least 29 mole rats per hectare, each adult weighing around a kilogram. Like the guinea pig (Cavia porcellus), which forms a major source of protein for people living today in the high Andes of Peru and Bolivia – an estimated 65 million being eaten annually by Peruvians, mole rats are extremely easy to catch; an attractive proposition for consumers surviving under the stress of hypoxia. They also reproduce at a phenomenal rate Today, Andean people domesticate guinea pigs for the table. Until other sites of human habitation during the Bale ‘ice age’ whether the MSA people lived permanently at high elevation or migrated there seasonally, to gorge on mole rats, cannot be resolved.

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.

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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

Ancient proteins: keys to early human evolution?

A jawbone discovered in a Tibetan cave turned out to be that of a Denisovan who had lived and died there about 160,000 years ago (see: Denisovan on top of the world; 6 May, 2019). That discovery owed nothing to ancient DNA, because the fossil proved to contain none that could be sequenced. But the dentine in one of two molar teeth embedded in the partial jaw did yield protein. The teeth are extremely large and have three roots, rather than the four more common in modern, non-Asian humans, as are Denisovan teeth from in the Siberian Denisova Cave. Fortunately, those teeth also yielded proteins. In an analogous way to the genomic sequencing of nucleotides (adenine, thymine, guanine and cytosine) in DNA, the sequence of amino acids from which proteins are built can also be analysed. Such a proteomic sequence can be compared with others in a similar manner to genetic sequences in DNA. The Tibetan and Siberian dentine proteins are statistically almost the same.

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Triple helix structure of collagen, colour-coded to represent different amino acids (credit: Wikipedia)

At present the most ancient human DNA that has been recovered – from an early Neanderthal in the Sima de los Huesos in Spain – is 430,000 years old (see: Mitochondrial DNA from 400 thousand year old humans; December 2013). Yet it is proving difficult to go beyond that time, even in the cool climates that slow down the degradation of DNA. The oldest known genome of any animal is that of mtDNA from a 560–780 thousand year old horse, a leg bone of which was extracted from permafrost in the Yukon Territory, Canada. The technologies on which sequencing of ancient DNA depends may advance, but, until then, tracing the human evolutionary journey back beyond Neanderthals and Denisovans seems dependent on proteomic approaches (Warren, M. 2019. Move over, DNA: ancient proteins are starting to reveal humanity’s history. Nature, v. 570, p. 433-436; DOI: 10.1038/d41586-019-01986-x). Are the earlier Homo heidelbergensis and H. erectus within reach?

It seems that they may be, as might even earlier hominins. The 1.8 Ma Dmanisi site in Georgia, now famous for fossils of the earliest humans known to have left Africa, also yielded an extinct rhinoceros (Stephanorhinus). Proteins have been extracted from it, which show that Stephanorhinus was closely related to the later woolly rhinoceros (Coelodonta antiquitatis). Collagen protein sequences from a 3.4 Ma camel preserved in the Arctic and even from a Tanzanian 3.8 Ma ostrich egg shell show the huge potential of ancient proteomics. Most exciting is that last example, not only because it extends the potential age range to that of Australopithecus afarensis but into tropical regions where DNA is at its most fragile. Matthew Warren points out potential difficulties, such as the limit of a few thousand amino acids in protein sequences compared with 3 million variants in DNA, and the fact that the most commonly found fossil proteins – collagens –  may have evolved very little. On the positive side, proteins have been detected in a 195 Ma old fossil dinosaur. But some earlier reports of intact diosaur proteins have been questioned recently (Saitta, E.T. et al. 2019. Cretaceous dinosaur bone contains recent organic material and provides an environment conducive to microbial communities. eLife, 8:e46205; DOI: 10.7554/eLife.46205)

 

Multiple invention of stone tools

Steadily, the record of stone tools has progressed further back in time as archaeological surveys have expanded, especially in East Africa (Stone tools go even further back, May 2015). The earliest known tools – now termed Lomekwian – are 3.3 million years old, from deposits in north-western Kenya, as are cut-marked bone fragments from Ethiopia’s Afar region. There is no direct link to their makers, but at least six species of Australopithecus occupied Africa during the Middle Pliocene. Similarly, there are various options for who made Oldowan tools in the period between 2.6 and 2.0 Ma, the only known direct association being with Homo habilis in 2.0 Ma old sediments from Tanzania’s Olduvai Gorge; the type locality for the Oldowan.

The shapes of stone tools and the manufacturing techniques required to make them and other artefacts, are among the best, if not the only, means of assessing the cognitive abilities of their makers. A new, detailed study of the shapes of 327 Oldowan tools from a 2.6 Ma old site in Afar, Ethiopia has revealed a major shift in hominin working methods (Braun, D.R. and 17 others 2019. Earliest known Oldowan artifacts at >2.58 Ma from Ledi-Geraru, Ethiopia, highlight early technological diversity. Proceedings of the National Academy, v. 116, p. 11712-11717; DOI: 10.1073/pnas.1820177116). The sharp-edged tools were made by more complex methods than the Lomekwian. Analysis suggests that they were probably made by striking two lumps of rock together, i.e. by a deliberate two-handed technique. On the other hand, Lomekwian tools derived simply by repeatedly bashing one rock against a hard surface, not much different from the way some living primates make rudimentary tools. But the morphology of the Ledi-Geraru tools also falls into several distinct types, each suggesting systematic removal of only 2 or 3 flakes to make a sharp edge. The variations in technique suggest that several different groups with different traditions used the once lake-side site.

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Various 2.6 Ma old Oldowan stone tools from Ledi-Geraru, Ethiopia (credit: Braun et al., 2019)

Ledi-Geraru lies about 5 km from another site dated about 200 ka earlier than the tools, which yielded a hominin jawbone, likely to be from the earliest known member of the genus Homo. A key feature that suggested a human affinity is the nature of the teeth that differ markedly from those of contemporary and earlier australopithecines. It appears that the tools are of early human manufacture. The ecosystem suggested by bones of other animals, such as antelope and giraffe was probably open grassland – a more difficult environment for hominin subsistence. The time of the Lomekwian tools was one of significantly denser vegetation, with more opportunities for gathering plant foods. Perhaps this environmental shift was instrumental in driving hominins to increased scavenging of meat, the selection pressure acting on culture to demand tools sharp enough to remove meat from the prey of other animals quickly, and on physiology and cognitive power to achieve that.

See also: Solly, M. 2019. Humans may have been crafting stone tools for 2.6 million years (Smithsonian Magazine)

Neanderthal demographics and their extinction

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.

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

Continue reading “Neanderthal demographics and their extinction”

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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The Baishiya 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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