Homo Sapiens: Anatomically Modern Humans (AMH)

Experts hailed the discovery in 2015 as "stunning" -- 47 teeth found in a cave in southern China dated back to 80,0000 to 120,000 years ago, challenging widely accepted ideas about human evolution.

It suggested that Homo sapiens were in China at least 20,000 years earlier than early modern humans had been previously believed to have left Africa and spread around the world. It also tantalizingly hinted at the possibility that a different group of early humans could have evolved separately in Asia.



Not so fast, says the science in 2021. New research published Monday has suggested perhaps we shouldn't be so eager to rewrite the time line on human origins.

DNA analysis of two human teeth found in the same cave, called Fuyan, plus teeth and other fossilized remains from four other caves in the same region, suggested that it was unlikely early modern humans were in China so early.

"Our new research means it is very unlikely that Homo sapiens reached China before 50,000 years ago. It is always possible that our species reached the region more than 100,000 years ago, but we would have to say that there is no convincing evidence in favor of this at present," said Darren Curnoe, an associate professor at the Australian Museum Research Institute in Sydney and coauthor of the paper that published in the journal PNAS on Monday.

The researchers were able to extract DNA from 10 human teeth and establish the age of other materials in the caves, such as charcoal and animal teeth, using a range of different methods. The team found that the teeth were at least 16,000 years old, while the other materials were less than 40,000 years old.

"The 2015 study relied heavily on the results of a single dating method which determined the age of cave materials (flowstone) lying above and below the sediments containing the human teeth," he said via email. Flowstone is a sheetlike deposit of rock formed by flowing water.

"It is well understood that the most reliable dates come directly from the materials of interest to archaeologists, in this case, the human teeth. Our new (dates), including direct ages, are far younger than previously suggested."

The 2015 study measured the radioactive decay of uranium within cave deposits, not DNA.

Chris Stringer, research leader for human evolution at the Natural History Museum in London, said that the dates of Chinese fossilized teeth had always stood out and it was right to investigate them further using different methods.

However, he said the study, while interesting, didn't definitively rule out early modern humans in China before 50,000 years ago.



Complex family tree
Untangling human ancestry is a complicated business, and recent research has indicated the human family tree is much more bushy and less linear than the traditional "Out of Africa" narrative, which suggested modern humans originated in Africa and made their first successful migration to the rest of the world in a single wave between 50,000 and 70,000 years ago.

Many different ancient hominins existed and coexisted before Homo sapiens emerged as the lone survivor, and there was interbreeding between different groups of early humans.

Some of these groups -- like Neanderthals -- are easily identified through the fossil record and archaeological remains, but others -- like the Denisovans -- have been largely identified by their genetic legacy.

Maria Martinón-Torres, director of the National Research Center on Human Evolution in Spain and an author of the 2015 study, said she welcomed the new data on the early presence of modern humans in China.

However, she noted that the two teeth from Fuyan Cave were uncovered in 2019 and didn't belong to the original sample her team studied and published in 2015.

"The precise data about the location and morphology of the sample is crucial, but it is not provided in the paper," she said.

"I agree that we should be working in improving the dates of all sites of interest, especially with direct dating when possible. However, at the moment, there is an increasing number of samples that would support the presence of H. sapiens outside Africa before 50 ka (50,000 years ago)," she said via email.

She noted that there are other discoveries in Saudi Arabia, Israel, Sumatra and Laos, and another site in China where a jawbone has been found, that support the presence of Homo sapiens outside Africa before 50,000 years ago.





One of the main factors supporting the idea that early modern humans left Africa around 50,000 years ago is that there is a strong signal in the genes of present-day human populations.

"We would say that Out of Africa after 70,000 years ago seems to be the dominant picture. We can't preclude earlier dispersals in other regions, but certainly southern China seems to have been settled in this Out of Africa wave after 50,000 years ago," Curnoe said via email.

However, Martinón-Torres said this doesn't rule out the possibility that earlier groups of Homo sapiens wandered around Asia earlier -- just as groups of other early humans like Neanderthals and Denisovans did.

"We had no expectations about the dating of these fossils and sites and would have been pleased if we had confirmed an early dispersal. It would certainly have made the history of our species much older than generally believed, and perhaps more interesting," Curnoe said.

"Sadly, this seems not to be the case, at the least for southern China, according to our work."


Ancient DNA and multimethod dating confirm the late arrival of anatomically modern humans in southern China

PNAS February 23, 2021 118 (8) e2019158118; doi.org/10.1073/pnas.2019158118

Significance
Genetic studies show the founders of all living non-African populations expanded from Africa ca. 65 to 45 ka. This “late dispersal” model has been challenged by the discovery of isolated AMHs at caves in southern China suggested as early as ca. 120 ka. We assessed the age of early AMH fossils from five caves in this region using ancient DNA analysis and a multimethod geological dating strategy. We found they were much younger than previously suggested, with some remains dating to the Holocene owing to the complex depositional history at these subtropical caves. Current evidence shows AMHs settled southern China within the timeframe set by molecular data of less than ca. 50 to 45 ka and no earlier.

Abstract
The expansion of anatomically modern humans (AMHs) from Africa around 65,000 to 45,000 y ago (ca. 65 to 45 ka) led to the establishment of present-day non-African populations. Some paleoanthropologists have argued that fossil discoveries from Huanglong, Zhiren, Luna, and Fuyan caves in southern China indicate one or more prior dispersals, perhaps as early as ca. 120 ka. We investigated the age of the human remains from three of these localities and two additional early AMH sites (Yangjiapo and Sanyou caves, Hubei) by combining ancient DNA (aDNA) analysis with a multimethod geological dating strategy. Although U–Th dating of capping flowstones suggested they lie within the range ca. 168 to 70 ka, analyses of aDNA and direct AMS 14C dating on human teeth from Fuyan and Yangjiapo caves showed they derive from the Holocene. OSL dating of sediments and AMS 14C analysis of mammal teeth and charcoal also demonstrated major discrepancies from the flowstone ages; the difference between them being an order of magnitude or more at most of these localities. Our work highlights the surprisingly complex depositional history recorded at these subtropical caves which involved one or more episodes of erosion and redeposition or intrusion as recently as the late Holocene. In light of our findings, the first appearance datum for AMHs in southern China should probably lie within the timeframe set by molecular data of ca. 50 to 45 ka.

Two studies report new Homo sapiens fossils from the site of Bacho Kiro Cave in Bulgaria. "The Bacho Kiro Cave site provides evidence for the first dispersal of H. sapiens across the mid-latitudes of Eurasia. Pioneer groups brought new behaviours into Europe and interacted with local Neanderthals. This early wave largely predates that which led to their final extinction in western Europe 8,000 years later", says Jean-Jacques Hublin, director at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

An international research team, led by Jean-Jacques Hublin, Tsenka Tsanova and Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology, and Nikolay Sirakov and Svoboda Sirakova of the National Institute of Archaeology with Museum at the Bulgarian Academy of Sciences in Sofia, Bulgaria, renewed excavations at Bacho Kiro Cave in 2015. The most spectacular finds come from a rich, dark layer near the base of the deposits. Here the team uncovered thousands of animal bones, stone and bone tools, beads and pendants and the remains of five human fossils.



Protein analysis

Except for one human tooth, the human fossils were too fragmented to be recognized by their appearance. Instead, they were identified by analysing their protein sequences. "Most Pleistocene bones are so fragmented that by eye, one cannot tell which species of animal they represent. However, the proteins differ slightly in their amino acid sequence from species to species. By using protein mass spectrometry, we can therefore quickly identify those bone specimens that represent otherwise unrecognizable human bones", says Frido Welker, Postdoctoral Research Fellow at the University of Copenhagen and research associate at the Max Planck Institute for Evolutionary Anthropology.

To know the age of these fossils and the deposits at Bacho Kiro Cave, the team worked closely with Lukas Wacker at ETH Zurich, Switzerland, using an accelerator mass spectrometer to produce ages with higher precision than normal and to directly date the human bones.

"The majority of animal bones we dated from this distinctive, dark layer have signs of human impacts on the bone surfaces, such as butchery marks, which, along with the direct dates of human bones, provides us with a really clear chronological picture of when Homo sapiens first occupied this cave, in the interval from 45,820 to 43,650 years ago, and potentially as early as 46,940 years ago", says Helen Fewlass of the Max Planck Institute for Evolutionary Anthropology. "The radiocarbon dates at Bacho Kiro Cave are not only the largest dataset of a single Palaeolithic site ever made by a research team, but also are the most precise in terms of error ranges", say researchers Sahra Talamo from the University of Bologna and Bernd Kromer from the Max Planck Institute in Leipzig.



DNA sequencing

Though some researchers have suggested that Homo sapiens may have already occasionally entered Europe by this time, finds of this age are typically attributed to Neanderthals. To know which group of humans were present at Bacho Kiro Cave, Mateja Hajdinjak and Matthias Meyer of the genetics team led by Svante Pääbo at the Department of Evolutionary Genetics at the Max Planck Institute for Evolutionary Anthropology sequenced the DNA from the fragmented fossils bones.

"Given the exceptionally good DNA preservation in the molar and the hominin fragments identified by protein mass spectrometry, we were able to reconstruct full mitochondrial genomes from six out of seven specimens and attribute the recovered mitochondrial DNA sequences from all seven specimens to modern humans. Interestingly, when relating these mtDNAs to those of other ancient and modern humans, the mtDNA sequences from Layer I fall close to the base of three main macrohaplogroups of present-day people living outside of Sub-Saharan Africa. Furthermore, their genetic dates align almost perfectly with those obtained by radiocarbon", says Mateja Hajdinjak, Postdoctoral Fellow at the Francis Crick Institute in London and research associate at the Max Planck Institute for Evolutionary Anthropology.

The results demonstrate that Homo sapiens entered Europe and began impacting Neanderthals by around 45,000 years ago and likely even earlier. They brought into Bacho Kiro Cave high quality flint from sources up to 180 km from the site which they worked into tools like pointed blades perhaps to hunt and very likely to butcher the remains of the animals found at the site.

"The animal remains from the site illustrate a mix of cold and warm adapted species, with bison and red deer most frequent", says palaeontologist Rosen Spasov from the New Bulgarian University. These were butchered extensively but were also used as a raw material source. "The most remarkable aspect of the faunal assemblage is the extensive collection of bone tools and personal ornaments", says zooarchaeologist Geoff Smith from the Max Planck Institute for Evolutionary Anthropology. Cave bear teeth were made into pendants, some of which are strikingly similar to ornaments later made by Neanderthals in western Europe.

Homo sapiens replaced Neanderthals

Taken together, the Bacho Kiro Cave sediments document the period of time in Europe when Middle Paleolithic Neanderthals were replaced by Upper Paleolithic Homo sapiens (the so-called transition period), and the first Homo sapiens assemblages are what archaeologists call the Initial Upper Paleolithic. "Up to now, the Aurignacian was thought of as the start of the Upper Paleolithic in Europe, but the Initial Upper Paleolithic of Bacho Kiro Cave adds to other sites in western Eurasia where there is an even older presence of Homo sapiens", notes Nikolay Sirakov of the National Institute of Archaeology with Museum at the Bulgarian Academy of Sciences.

"The Initial Upper Paleolithic in Bacho Kiro Cave is the earliest known Upper Palaeolithic in Europe. It represents a new way of making stone tools and new sets of behaviour including manufacturing personal ornaments that are a departure from what we know of Neanderthals up to this time", says Tsenka Tsanova of the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology. "The Initial Upper Paleolithic probably has its origin in southwest Asia and soon after can be found from Bacho Kiro Cave in Bulgaria to sites in Mongolia as Homo sapiens rapidly dispersed across Eurasia and encountered, influenced, and eventually replaced existing archaic populations of Neanderthals and Denisovans."

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Abstract
The Middle to Upper Palaeolithic transition in Europe witnessed the replacement and partial absorption of local Neanderthal populations by Homo sapiens populations of African origin1. However, this process probably varied across regions and its details remain largely unknown. In particular, the duration of chronological overlap between the two groups is much debated, as are the implications of this overlap for the nature of the biological and cultural interactions between Neanderthals and H. sapiens. Here we report the discovery and direct dating of human remains found in association with Initial Upper Palaeolithic artefacts2, from excavations at Bacho Kiro Cave (Bulgaria). Morphological analysis of a tooth and mitochondrial DNA from several hominin bone fragments, identified through proteomic screening, assign these finds to H. sapiens and link the expansion of Initial Upper Palaeolithic technologies with the spread of H. sapiens into the mid-latitudes of Eurasia before 45 thousand years ago3. The excavations yielded a wealth of bone artefacts, including pendants manufactured from cave bear teeth that are reminiscent of those later produced by the last Neanderthals of western Europe4,5,6. These finds are consistent with models based on the arrival of multiple waves of H. sapiens into Europe coming into contact with declining Neanderthal populations7,8.



Jean-Jacques Hublin et al.
Initial Upper Palaeolithic Homo sapiens from Bacho Kiro Cave, Bulgaria
Nature, 11 May 2020, DOI: 10.1038/s41586-020-2259-z

Helen Fewlass et al.
A 14C chronology for the Middle to Upper Palaeolithic transition at Bacho Kiro Cave, Bulgaria
Nature Ecology and Evolution, 11 May 2020, DOI: 10.1038/s41559-020-1136-3