Did Chinese Homo erectus survive into the Late Pleistocene?

14,000-year-old hominin thigh bone has archaic affinities.

In 2012, human remains differing from the modern condition were reported from two sites 300 km (185 miles) apart in southwest China: Longlin Cave in Guangxi Province, and Maludong (‘Red Deer Cave’) in Yunnan Province. The Longlin remains have been radiocarbon dated to 11,500 years old, and those from Maludong to 14,000 years old. The Longlin remains included a partial skull, a temporal bone fragment probably belonging to the skull, a partial lower jawbone and some fragmentary postcranial bones. The cheek bones of the skull are broad and flared sideways; the browridges conspicuous; the chin less prominent than in Homo sapiens; and the remains are very robust. The Maludong remains include a skullcap, two partial jawbones and a partial thighbone.

Popularly reported as the Red Deer Cave people, the hominins were at first thought to represent a single population, but newly-published work suggests that the Longlin skull has affinities to early modern humans. The bony labyrinth (the bony outer wall of the inner ear) of the temporal bone fragment is modern in appearance and it is possible that the skull’s unusual shape might be the result of interbreeding between archaic and modern humans. It has been suggested that Longlin was located in a ‘hybrid zone’ – a border between relict archaic and modern populations. Similar hybrid zones occur with some non-human primate populations.

The Maludong thighbone is now claimed to show affinities to archaic humans, in particular those from the Early Pleistocene. There is a scarcity of later archaic human remains in East Asia, and the authors of the new report are reluctant to assign the thighbone to a particular archaic human species. However, the likeliest possibility is that the thighbone represents a late survival of Homo erectus in China. Regardless of species, the implications of these new findings is that isolated populations of archaic humans were still in existence in China as late as 11,500 years ago and that some of these populations were interbreeding with modern humans.

References:

1.  Curnoe, D. et al., Human Remains from the Pleistocene-Holocene Transition of Southwest China Suggest a Complex Evolutionary History for East Asians. PLoS One 7(3) (2012).
2.  Curnoe, D., Ji, X., Taçon, P. & Yaozheng, G., Possible Signatures of Hominin Hybridization from the Early Holocene of Southwest China. Scientific Reports 5, 12408 (2015).
3.  Curnoe, D. et al., A Hominin Femur with Archaic Affinities from the Late Pleistocene of Southwest China. PLoS One (2015).

 

 

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New dates for Monte Verde pushes back arrival of first humans in South America

Chilean site was first occupied at least 18,500 years ago

Monte Verde in southern Chile is a peat bog in the terraces of Chinchihuapi Creek in the Maullín river basin, midway between the Pacific coast and the Andean mountains. There is well-preserved evidence of human occupation including wooden tent remains, foundations and floors of huts, hearths, wooden lances, mortars, and large numbers of stone tools. The site was apparently occupied all year round. A wide range of coastal and mountain habitats were exploited including marshes, wetlands, forests, estuaries, and rocky and sandy shorelines.

Evidence of habitation was not thought to pre-date the 14,600 year horizon identified at the site MV-II, although there was evidence of an earlier cultural horizon (MV-I). The MV-II dates in themselves made Monte Verde attractive to opponents of the long-running ‘Clovis First’ orthodoxy, which holds that the culture originally identified at Clovis, New Mexico represents the earliest human settlement of the New World. The Clovis culture is noted for its distinctive leaf-shaped spear points, which were first found in the 1930s. Clovis sites dating from 13,250 years ago are widespread across the United States and Central America to as far south as Panama. Assuming that the first Americans reached the New World via the Beringia land bridge that linked Alaska with Siberia during the last Ice Age, a human presence in South America 14,600 years ago is problematic to Clovis First.

However, even earlier dates have now been obtained for Monte Verde. Archaeologists carried out spatially-intermittent excavations and core drillings across an area lying between MV-II and the two sites of CH-I and CH-II, located on the south side of the creek, 500 m upstream of MV-II. These revealed stone tools, faunal remains, and evidence of fires widespread across the study area albeit vertically and horizontally discontinuous. These appear to represent ephemeral seasonal activities carried out over a long period of time between shallow channels of a now-buried braided system of streams that fed into the river. Radiocarbon and Optically Stimulated Luminescence dating has yielded a range of dates from 18,500 to 14,500 years ago, with implications that humans reached the New World much earlier than previously believed.

Reference:
Dillehay, T. et al., New Archaeological Evidence for an Early Human Presence at Monte Verde, Chile. PLoS One 10 (11) (2015).

 

 

Homo erectus origin likely for Flores ‘hobbits’

Dental study rejects modern human or earlier hominin connection with Homo floresiensis

The origin of the diminutive ‘hobbits’ of Flores, Indonesia have been controversial since they were announced as a new human species, Homo floresiensis, in 2003. The most widely accepted view is that they are descended from a group of Homo erectus that reached Flores at least a million years ago and underwent a phenomenon known as insular dwarfism whereby a combination of low risk of predators and a relative scarcity of food means that smaller individuals are favoured from an evolutionary point of view and thus individuals within a population will ‘downsize’ over the course of many generations.

However, there are two alternative viewpoints. The first is that the Homo floresiensis remains simply represent modern humans affected by a condition such as microcephaly or cretinism. The second view accepts that the Flores hominins are indeed descended from an archaic species, but posit that it is something more primitive than Homo erectus – possibly Homo habilis or an australopithecine. It is argued that the absence of fossil evidence for such early hominins leaving Africa is not evidence of absence from Eurasia.

In a newly-published study, researchers carried out extensive comparisons using linear metric analyses, crown contour analyses, and other trait-by-trait morphological comparisons of the molar, premolar and canine teeth of Homo floresiensis against an extensive sample of teeth from present-day modern, prehistoric modern, and archaic humans. Three methods were used: metric analyses based on crown length and breadth data; comparisons of crown contour using normalized Elliptic Fourier Analysis (EFA); and non-metric and linear metric comparisons of individual morphological traits not recorded by the first two methods.

The researchers found suggest that the Homo floresiensis teeth do share derived characteristics with those of Early Pleistocene Homo erectus from East Africa and Java, and with the Dmanisi hominins from Georgia; but none of the ‘hobbit’ teeth exhibit the very primitive morphology associated with Homo habilis or australopithecines. Such characteristics include the occasional absence of a P3 buccal groove, a distally positioned P3 lingual cusp, a more circular P4 crown, the presence of a P4 transverse crest, non-parallelogram M2 crown shape, a mesiodistal short M2 crown, a M1 mid-trigonid crest, equivalent M1 and M2 sizes, and a moderately wide upper dental arcade. The findings rule out the claim that Homo floresiensis evolved from a hominin that was more primitive than Homo erectus.

Nor was a good match found with the modern samples. In comparison to Homo floresiensis, the teeth of Homo sapiens are derived for nine out of 26 character states, contradicting the suggestion that the dentition of Homo floresiensis is wholly modern.
Overall, the results suggest that Homo erectus is the ancestral species; however the dentition of Homo floresiensis did continue to evolve and possesses some unique features not seen in any other hominin species. These include the large (relative) size and the unique occlusal morphology of the P3 that otherwise exhibits primitive morphologies; and the extremely short first molars. In view of the general trend of molar shortening during the evolution of Homo over time, this condition in Homo floresiensis is actually more derived than in Homo sapiens.

It must be assumed that these evolutionary changes reflected the unique habitat of Flores, but regardless they demonstrate the distinctiveness of Homo floresiensis as a species.

Reference:
Kaifu, Y. et al., Unique Dental Morphology of Homo floresiensis and Its Evolutionary Implications. PLoS One 10 (11) (2015).

Bronze Age origins of bubonic plague

Study finds evidence of Yersinia pestis bacterium in 5,000-year-old human teeth

Three pandemics of bubonic plague have occurred in historical times: the first began with Plague of Justinian from AD 541 to 544, continuing intermittently until AD 750 AD; the second began with the Black Death from AD 1347 to 1351, continuing in waves including the Plague of 1665-66 into the eighteenth century; and the third which started in China in the mid-nineteenth century and triggered a series of outbreaks worldwide during the first half of the last century. The Black Death alone killed 30 to 50 percent of the European population. Deaths totalled at least 75 million, more than the number of deaths during World War I and II combined.

The cause of this deadly disease was identified as the flea-borne bacterium Yersinia pestis in 1894 by Swiss biologist Alexandre Yersin. More recently, genetic studies have suggested that it diverged from the more widespread but less virulent Yersinia pseudotuberculosis anywhere between 2,600 and 28,000 years ago.

In a newly-published study, researchers investigated the origins of Y. pestis by sequencing ancient bacterial genomes obtained from the teeth of Bronze Age people across Eurasia dating from 2,800 to 5,000 years ago. Their findings indicate that the flea-borne strain that caused the historic period plague pandemics evolved from a less virulent strain that was present in human populations long before any records of plague outbreaks.

The strains infecting Bronze Age Eurasian populations lacked the Yersinia murine toxin (ymt) gene, which encodes a phospholipase D protecting the bacterium inside the flea gut, so enabling fleas to act as vectors. Similarly, mutations associated with the development of bubonic plague and evading mammalian immune systems had not yet occurred. Not until around 3,000 years ago did highly virulent, flea-borne strains emerge.

The researchers also estimated the divergence from Y. pseudotuberculosis at 55,000 years ago, twice as early as previous maximum estimates. The Bronze Age strains began to diverge from one another 5,800 years ago. Although they could not cause bubonic plague, they could still cause pneumonic and septicemic plague and these might have been responsible for population declines between the late fourth and early third millennium BC. Large scale population movements and social changes during the Bronze Age might have facilitated plague outbreaks, but not on the scale of the historical era flea-borne pandemics.

Reference:

Rasmussen, S., Allentoft, M., Nielsen, K., Orlando, L. & Sikora, M., Early Divergent Strains of Yersinia pestis in Eurasia 5,000 Years Ago. Cell 163, 571-582 (2015).

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Modern humans were in China 100,000 years ago

Assignment of fossil teeth from Fuyan Cave to Homo sapiens is ‘unequivocal’

Ever since genetic evidence emerged to support the ‘recent Out of Africa’ model of modern human origins, the orthodox view is that until around 60,000 years ago modern humans were confined to Africa and a short range extension into Southwest Asia. The latter is thought to have been brought to an end as colder, more arid climatic conditions set in around 90,000 years ago. The model has been challenged by archaeological evidence suggesting that modern humans were established on the Arabian Peninsula 125,000 years ago and had reached India 77,000 years ago.

What has up until now been lacking is unequivocal fossil evidence significantly earlier than around 45,000 years old. Controversial evidence had previously been reported from two sites in southern China. An age of up to 139,000 years old has been claimed for the Liujiang Skull, discovered in 1958, but the exact geological position of the find was not documented and the skull could actually be as little as 30,000 years old. A lower jawbone and two molar teeth from Zhirendong (‘Homo sapiens cave’) in Guizhou Province have been securely dated to 106,000 years old, but it is not certain that these remains belonged to a modern human.

However, the discovery has now been reported of 47 teeth at the newly-excavated site of Fuyan Cave in Daoxian, Hunan Province. Uranium series dating of associated stalagmite fragments gave a minimum age of 80,000 years old for the teeth and faunal dating gave a maximum age of 120,000 years old. The teeth were compared with those of Late Pleistocene humans from Europe, Asia and Africa and were found to fall consistently within the Homo sapiens size range. They are generally smaller than other Late Pleistocene samples from Asia and Africa, and are closer to European Late Pleistocene samples and the teeth of present-day people. They resemble the latter far more closely than they do the teeth of Neanderthals or Homo erectus.

The announcement adds a radical new dimension to the history of modern human dispersals in Eurasia.

Reference:
Liu, W. et al., The earliest unequivocally modern humans in southern China. Nature 526, 696-699 (2015).

Ancient DNA reveals more extensive Neolithic back migrations to Africa from Eurasia

Sequenced genome of 4,500-year-old Ethiopian male provides genetic baseline for researchers

Modern humans are generally accepted to have originated in Africa, and the genomes of native Africans is therefore of great importance in reconstructing early migrations as our species dispersed around the world as it provides a baseline against which later events can be viewed. A problem for geneticists is the back migrations from Europe and Southwest Asia that have occurred within historical times, which act as a confounding factor when working with genetic data from present-day populations.

One way by which the problem could be solved is to obtain ancient DNA from prehistoric human remains, but this has proved difficult with only mitochondrial DNA being obtained up until now. However, in 2012, archaeologists excavated the burial of an adult male in Mota Cave, a riverside cave discovered the year before in the highlands of southwestern Ethiopia. Radiocarbon remains established that the remains were 4,500 years old, predating Eurasian migrations and the dispersal of Bantu farmers which spread agriculture across much of sub-Saharan Africa.

Conditions in the cave favoured the survival of ‘Mota’s’ DNA and it proved possible to sequence his genome. It was found that he was closely related to present-day Ethiopian populations, and in particular to the Ari, a group of Omotic speakers from southern Ethiopia, located to the west of the highland region where Mota lived. This was unsurprising and confirmed the view that there had been population continuity in this relatively isolated region over the last 4,500 years.

The researchers then searched for the source of the later Eurasian admixture by assuming that the present-day Ara genome is a genetic mix of Mota plus the source. It was found that the closest match was with Neolithic LBK farmers from Stuttgart and with present-day Sardinians. The latter are known to be the closest contemporary match to early Eurasian Neolithic farmers. The implication is that the genetic backflow into Africa came from the same source as the Neolithic expansion into Europe from Anatolia. These farmers were presumably responsible for the archaeologically-attested arrival of wheat, barley and other domesticated Southwest Asian crops in Africa around 3,000 years ago.

The next step was to use Mota as an African genetic baseline and the Neolithic LBK as the source of the Eurasian component to estimate the magnitude and geographic extent of historical migrations, without having to use present-day populations. It was found that the Eurasian genetic backflow was substantially higher than previously believed, with an additional 4 to 7 percent of the genome of most African populations tracing back to a Eurasian source. The geographical impact was also far greater than previous estimates suggest, extending all the way to West and South Africa. Even the Yoruba and Mbuti, often used as baselines in genetic studies, were found to have a significant Eurasian component, albeit less than in East Africa.

The Mota data has thus proved to be extremely informative about Neolithic migrations and obtaining even earlier African genomes would be highly desirable. Unfortunately, the African climate does not favour the preservation of DNA, but it is to be hoped that as sequencing techniques improve more ancient African genomes will become available.

Reference:
Llorente, M. et al., Ancient Ethiopian genome reveals extensive Eurasian admixture throughout the African continent. Science 350 (6262), 820-822 (2015).

Congenital defect is possible further evidence of inbreeding by Neanderthals at El Sidrón

High incidence of congenital clefts of the arch of the atlas observed among remains from Spanish site

The Atlas (C1) vertebra is the first cervical vertebra of the spine, immediately below the skull. It takes its name from the Greek Titan Atlas, who is popularly (but incorrectly) supposed to have held the world on his shoulders. Congenital defects of the anterior or posterior arches are rare in modern populations, occurring at frequencies of 0.087 to 0.1 percent and 0.73 to 3.84 percent respectively. The condition does not normally lead to clinical symptoms.

El Sidrón is a cave site in Asturias, northern Spain that has yielded extensive Neanderthal remains and stone tools since these were first discovered there in 1994. Over 2,400 human fossils have been recovered, representing at least thirteen individuals including seven adults, three adolescents, two juveniles and one infant. The remains are 49,000 years old. Ancient DNA has previously been obtained from the remains, indicating a small patrilocal (mature males remain within their family birth group, but females come from outside) group with low genetic diversity. Dental hypoplasias indicate that around half of the group members had experienced episodes of growth arrest due to malnutrition.

Researchers now report that two out of just three well-preserved atlases from the site present respectively a defect of the posterior arch and the anterior arch. Such a high incidence of a rare condition could be interpreted as further evidence of low genetic diversity of the group, and as a possible indicator of inbreeding. The picture that emerges from El Sidrón is of a small, barely-viable Neanderthal group struggling for survival in extremely harsh conditions.

References:
Ríos, L. et al., Possible Further Evidence of Low Genetic Diversity in the El Sidrón (Asturias, Spain) Neandertal Group: Congenital Clefts of the Atlas. PLoS One 10 (9), e0136550. (2015).