Patagonian monsters: July 2020

Saturday, July 25, 2020

H. luzonensis and H. floresiensis possible link to Denisovans

Just a brief post to share a paper published yesterday (Introgression, hominin dispersal and megafaunal survival in Late Pleistocene Island Southeast Asia Joao C Teixeira, Guy S Jacobs, Chris Stringer, Jonathan Tuke, Georgi Hudjashov, Gludhug A Purnomo, Herawati Sudoyo, Murray P Cox, Ray Tobler, Chris SM Turney, Alan Cooper, Kristofer M Helgen bioRxiv 2020.07.24.219048; doi: https://doi.org/10.1101/2020.07.24.219048).

The authors were looking into the "super-archaic" hominins that were discovered in the Island Southeast Asia (ISEA) region: Homo luzonensis and H. floresiensis, which were contemporary to anatomically modern humans (AMH). As modern populations in the region have a high level of Denisovan introgression they wanted to find out if there was also a signal of introgression from the super-archaics in the region.

Their analysis failed to detect super-archaic admixture but they reached an interesting conclusion:

"An alternative explanation is that H. luzonensis and H. floresiensis belong to a hominin clade that is considerably less divergent from AMH than is currently accepted, possibly being the latesurviving descendants of an earlier radiation of a Denisovan-like lineage across ISEA.
This would imply that hominin occupation of Flores (1.2Ma) and the Philippines (700ka) was not continuous and that the ubiquitous Denisovan ancestry across ISEA, which includes signals of admixture from a Denisovan population that diverged from the Altai Denisovans ~280ka, results from AMH admixture with one or both of these groups.
Indeed, the patterning of Denisovan ancestry across ISEA is consistent with separate Denisovan introgression events in the Philippines and, potentially, in Flores. Despite the complete lack of support for this scenario from current morphological interpretations, it is possible that pronounced dwarfism and prolonged periods of endemic island evolution for H. floresiensis and H. luzonensis complicate morphological assessments and phylogenetic placement of these groups.
While it would simplify the search for ‘southern Denisovans’ if they could be linked with the dwarfed hominins of Flores and Luzon, existing archaeological and morphological data and Flores as a more likely location for the sources of Denisovan-like DNA."

Below a map of the sites where Denisovan, Flores and Luzon hominins' remains were found:

Could the Denisovans be a link to the Homo erectus population of Asia? Current research links them to Neandertals in western Eurasia.

Thursday, July 23, 2020

Chiquihuite Cave occupied 35,000 years ago? A very early date for human presence in America

This paper, published in Nature yesterday: Ardelean, C.F., Becerra-Valdivia, L., Pedersen, M.W. et al. Evidence of human occupation in Mexico around the Last Glacial Maximum. Nature (2020). https://doi.org/10.1038/s41586-020-2509-0, found evidence that human beings lived in the Chiquihuite Cave for around 20,000 years, starting some 35 ky ago.

The cave is located in north central Mexico (see map) in a dry area, which at the time had forests that resembled those we now see in British Columbia or NW USA.

The authors unearthed stone tools in the cave but these are quite unusual: "The site yielded about 1,900 stone artefacts within a 3-m-deep stratified sequence, revealing a previously unknown lithic industry that underwent only minor changes over millennia.". That is, a technology that produced stone tools in the same manner over thousands of years and in a way that is different from other stone making tools!

People have been living here since before the Last Glacial Maximum (LGM) which took place between 19 and 26,000 years ago. This is long before the purporte "Beringian" standstill, (theory which assumes that Asians on their way to America stood still in Beringia because the LGM didn't let them into America).

The stones! the authors state: "The flaked artefacts reflect a technological tradition that was previously unknown, and remains mostly unchanged over the sequence." and they are quite unique: "...However, the majority of these tools are unifacial with marginal retouch... Apart from incipient preforms, finished bifacial artefacts are scarce; their existence is inferred from the abundance of tertiary thinning flakes. Notches and stems are almost completely absent. The bases are rounded or convergent, and are rarely thinned... Overall, the assemblage represents a lithic industry with no evident similarities to any of the other cultural complexes of the Pleistocene or Early Holocene epochs known in the Americas".

The authors conclude: "The occupants of the cave were seemingly adapted to altitudes and mountain landscapes, showing a behavioural pattern that—to our knowledge—was previously unknown in the archaeological record of the Americas. Their lithic industry has no parallel in the continent and its qualitative traits suggest a mature technology, possibly brought in from elsewhere before the LGM."

Of course the unusual stone tools and the lack of bones, ashes or hearths which would indicate actual human presence has been used by some skeptics to doubt the validity of this find. I quote some of them from this article in National Geographic below:

Loren Davis,Oregon State archaeologist: "The thing to remember is that humans don’t have a monopoly on the physics required to break rocks" (implying a natural origin for the unusual stone tools.
Tom Dillehay -discoverer of the Monteverde Site in Chile- "It's very curious that the assemblage is so different from anything anyone has known before. How is it possible that it’s not related to anything previously found? Well, it’s possible."

These are some of the tools (from the article):

They look man-made to me. And the tools found inside the cave were from stones of a green or black color (90% of the total) wich is interpreted as an act of human choice. Furthermore these stones are found close to the cave but not in it. The cave's rocks are grey so there is no doubt that they didn't fall from the cave's walls or roof.

To my inexperienced and non-academic eyes they look rather coarse and similar to Mousterian tools made by Neanderthals.

There is much to learn yet! But if humans were using these caves 35 Ky ago, then they must have arrived even earlier. In a Spanish language article one of the paper's authors -Ardelean- tells us that they found the cave following the indications given to them by a local farmer. That it took him a lot of work and effort to secure funding to excavate the cave; that there are few discoveries like this due to lack of funding and that the scarce funding goes into the "pyramids" (Mayan and Aztec ones) because they can be exploited as tourist attractions.

Ardelean added that "humans came to the caves now and then, they didn't live there, instead it was a winter shelter, probably part of a migration route".

Let's look forward to more discoveries like this one.

Wednesday, July 22, 2020

Nature article supports arrival of first Americans as far back as 57 Ky ago

An article published in Nature today (The timing and effect of the earliest human arrivals in North America Becerra-Valdivia, L., Higham, T. Nature (2020). https://doi.org/10.1038/s41586-020-2491-6 ) finds that:

"The data obtained show that humans were probably present before, during and immediately after the Last Glacial Maximum (about 26.5–19 thousand years ago)2,3 but that more widespread occupation began during a period of abrupt warming, Greenland Interstadial 1 (about 14.7–12.9 thousand years before 2000)4. We also identify the near-synchronous commencement of Beringian, Clovis and Western Stemmed cultural traditions, and an overlap of each with the last dates for the appearance of 18 now-extinct faunal genera. Our analysis suggests that the widespread expansion of humans through North America was a key factor in the extinction of large terrestrial mammals."

It is a first step in the right direction, and clearly states: "If transatlantic migration is set aside and an Asian origin assumed, the antiquity and distribution of the early sites suggest that the initial crossing of the 48th parallel north occurred either (i) during the later part of Marine Isotope Stage 3 (57–29 ka)36, when ice and sea level estimates37–39 indicate that land passage through Beringia was unlikely or interrupted, and an ice-free corridor between the Laurentide and Cordilleran Ice Sheets was probably present39 (with evidence of terrestrial landscapes occurring between 48 and 40 ka40) or (ii) during the LGM terminus, when the Bering land bridge was viable but the ice-free corridor was inaccessible41,42. Both possibilities sug-gest the earliest arrivals to North America had some degree of littoral adaptation."

The Clovis First theory has bean dealt a great blow! The authors write: "the previously accepted model (termed ‘Clovis-first’)—suggesting that the first inhabitants of the Americas were linked with the Clovis tradition, a complex marked by distinctive fluted lithic points1—has been effectively refuted".

It mentions several Pre-Clovis sites: "pre-Clovis sites show the earli-est evidence for cultural occupation in stratigraphic component C of Chiquihuite Cave (Mexico) at 33,150–31,405 cal., before the Last Glacial Maximum (LGM) (from 26.5 to 20–19 ka2,3). Several sites appear to be occupied later, during or immediately after the LGM. These include Gault (26,435–17,385cal.), Meadowcroft Rockshelter (24,335–18,620cal.) and Cactus Hill (20,585–18,970cal.) (Fig.2a). In eastern Beringia, Bluefish Caves is represented by a single date obtained on a humanly modified bone sample (24,035–23,310cal.) dating squarely to the LGM..

It is encouraging, and should undo the dark work of William Henry Holmes of the Smithsonian Institution, Thomas Chamberlin of the United States Geological Survey and Ales Hrdlicka (of the Smithsonian) who refused to accept that humans had reached America before the end of the last Ice Age. They imposed their ideas and only accepted an earlier (but not too early) date when the Folsom points were found in 1927 followed by the Clovis ones in the 1930s. They were irrefutable confirmation of ancient humans in the Americas during the Pleistocene.

But pushing the dates beyond 12-13,000 years has proven difficult. Let's hope this article marks a new trend in the field.

Saturday, July 18, 2020

The Neanderthal from Chagyrskaya

A recent paper (A high-coverage Neandertal genome from Chagyrskaya Cave by Fabrizio Mafessoni et al. Proceedings of the National Academy of Sciences Jun 2020, 117 (26) 15132-15136; DOI: 10.1073/pnas.2004944117) reported the sequencing of a third Neandertal genome. It complements the other two, one from the Denisova Cave in the Altai Mountains, the other from the Vindija cave in Croatia.

The Neandertal from Chagyrskaya -a site which is roughly 66 miles (106 km) from Denisova is significant because Chagyrskaya specimen lived around 80,000 years ago, the Denisovan Neandertal lived roughly 110,000 years ago and Vindija's specimen has been dated to around 50,000 years ago.

But despite the geographical closeness between Chagyrskaya and Denisova, Chagyrskaya is closer to the European Neanderthals: it "...shares more derived alleles with Vindija 33.19 and other later Neandertals in the Caucasus and in Europe than with the older Denisova 5 Neandertal from the Altai".

The authors also found that " that Vindija 33.19 is more closely related than Chagyrskaya 8 to Neandertal populations that contributed the majority of the DNA to present-day populations." that is, modern humans are closr to Vindija Neandertals than to the Chagyrskaya one.

Finally, they conclude that "Chagyrskaya 8 is thus related to Neandertal populations that moved east sometime between 120 and 80 kya. Interestingly, the artifacts found in Chagyrskaya Cave show similarities to artifact assemblages in central and eastern Europe, suggesting that Neandertal populations coming from western Eurasia to Siberia may have brought their material culture with them. Some of these incoming Neandertals encountered local Denisovan populations, as shown by Denisova 11, who had a Denisovan father and a Neandertal mother related to the population in which Chagyrskaya 8 lived."

Friday, July 17, 2020

Amerindians navigated to Polynesia before the Polynesians arrived there

An article in Nature (Native American gene flow into Polynesia predating Easter Island settlement, Ioannidis, A.G., Blanco-Portillo, J., Sandoval, K. et al. Nature (2020). https://doi.org/10.1038/s41586-020-2487-2) finds evidence that there is Amerindian admixture in Polynesian people due to an early "one-time-only" event that took place around 1150-1230 AD in eastern Polynesia.

The Amerindians didn't sail to Easter Island (Rapa Nui) which is the point where America and Polynesia are closest. Instead they moved across the equatorial region -like Thor Heyerdahl had suggested in the 1940s- and reached the Marquesas islands, which at that time were uninhabited.

Then came the island-hopping Polynesians from the west and they met there, admixed and then spread across the Pacific.

The authors find similarities between the DNA sampled in Polynesia with the DNA of Colombian and Ecuadorian Native Americans.

A plausible alternative is that the Amerindians never set sail across the ocean. Instead the Polynesians kept on sailing eastwards and reached America, here they fraternized with the locals and returned with Amerindian DNA back home.

The Polynesia to America route has been proposed before (Diffusionism Reconsidered: Linguistic and Archaeological Evidence for Prehistoric Polynesian Contact with Southern California Terry L. Jones and Kathryn A. Klar American Antiquity, Vol. 70, No. 3 (Jul., 2005), pp. 457-484 DOI: 10.2307/40035309). And I have posted about Polynesian DNA in South America (here) regarding the Botocudo people and a possible route for peopling America via the Antarctic (read more ), but for pre-Polynesian people -I was thinking about Aboriginals from Australia or even pre-sapiens hominins (here), not Polynesians who are the latecomers to the region.

Alternate Hypothesis

Perhaps the Amerindian signal has another origin. Let's take a look at the map in Nature's paper:

See large size map

The "Polynesians" supposedly have a strong imprint of Amerindian -green- DNA. And the Chilean Mapuche people (brown) are found in large amounts in Easter Island, which is coherent with the Spanish from Chile visiting the islands with native servants-laborer, and from there back migrated into western Polynesia in historic times. They also occupy the Chilean-Argentine area of South America. The ancestral Kaweskar people who were "canoe people" have a high prevalence of the "green" signal. They were the first to reach southern South America.

The strong Mesoamerican signal may (green) may indicate that these people (Mixe, Zapotec, Maya, Northern South American Amerindians and the ancestral Kaweskar) came from Polynesia -from Asia via Polynesia. They also settled there in their migration from Asia to America. Later came the (pale blue) wave of Polynesians and replaced them.

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