This new paper in Nature (click on screenshot, pdf here, reference at bottom) has the potential to be the big human-paleobiology story of the last several years. It reports finding human occupancy of a high-altitude cave in Mexico during the last glacial maximum (LGM): about 26,000 years ago. And that, say the authors, implies that humans have been in the New World since more than 30,000 years ago—more than doubling the time we thought they’d been here. Previously, the best guess was that humans crossed the Bering Strait from Siberia about 15,000 years ago, and then spread through the Americas.
Click on the screenshot below to get the paper (free through the legal app Unpaywall, or you can make a judicious inquiry).
Before we accept these results as overturning the received wisdom about humans in the New World, though, there has been some criticism of the paper, as you can see in a precis in Science by Andrew Curry.
The cave where the finds were made sits atoop a remote mountain in the Mexican state of Zacatecas, about 2,740 m high, and has been studied since 2012. Although dry and barren now, it was thought to be verdant during the LGM, with water, plants, and plenty of edible animals nearby. Researchers worked there for a month at a time, camping in the cave and hauling water and food by donkey from the nearest town.
What made the researchers suppose that the cave was occupied by humans were several things, most prominently 2000 specimens of what looked like sculpted tools. Here’s a figure showing some of these putatively manufactured objects:
Now I would have thought that by now paleoanthropologists would be able to distinguish non-human rock artifacts from real, chipped tools, but apparently that’s not the case. As one critic says in the Science writeup:
Critics point out that the tools are simple and don’t resemble other toolkits from the Americas, raising the possibility they’re the product of natural breakage. “They look like they could be artifacts, but why aren’t they found anywhere else in the landscape?” wonders David Meltzer, an archaeologist at Southern Methodist University. The tools’ consistency is also remarkable, he says. “If these tools are real, why are they only found—so far at least—in this one spot over a 10,000-year period? Humans adapt and adopt new technology.”
The tool-making conclusion, at least, must remain tentative. There was also burned wood that was radiocarbon dated, implying human campfires, but the critics again say that this could derive be from “wind-blown” wildfires. The researchers also used OSL dating of quartz from the sediments, which tells you when the mineral was last exposed to light, ergo when it was laid down.
Finally, the researchers trawled the cave for DNA, which they could sequence to see what kind of animals and plants were there. The fauna included bats, mice and other rodents, marmots, goats, and sheep, as well as birds, though this could have come from more recent occupancy. Plant DNA included forest species like spruce, pines, grasses, and palms. The disappearance of cold-adapted species and forest trees that gave way later to Joshua trees and grasses suggests that the sediments in the cave did go through the late Glacial Maximum, which was followed by a period of dryness.
Notably, no human or humanoid DNA was found in the cave, which would have gotten people much more excited about this find.
THE UPSHOT
How strong is the evidence for human presence in the Americas beginning 30,000 years ago? The 30,000 years is a guess by the authors, derived from guessing how long it would take humans to get to a 26,000-year-old cave residence in Mexico after crossing from Siberia. In terms of the age of the cave itself, that seems reasonable, but the evidence for human occupation is largely the “tools”, and their provenance is doubtful. And if humans inhabited the cave continuously for millennia, as the authors suppose, then why wasn’t human DNA found there? My judgment, and I’m a tyro here, is that the evidence is intriguing but not terribly strong. A lot hinges on whether the “tool-like” stone artifacts really were chipped by hominin hands.
On the other hand, the Science article says that there is a cave in the Yukon that’s yielded dates as old as the Mexican cave (about 24,000 years), but although it contains thousands of animal bones, there are “few stone tools or cut marks.” But other researchers are beginning to think that people came to America earlier than we thought, and could have spread quickly by traveling along the West coast by boat, avoiding the largely frozen interior. Here’s a tweet (h/t: Matthew) showing sites where there could have been earlier habitations:
News & Views: Two studies in Nature report evidence that the initial human settlement of the Americas happened earlier than is widely accepted. Some of the evidence suggests settlement began at least 10,000 years earlier than was generally suspected. https://t.co/OBuIQzBI7v
— Nature (@nature) July 23, 2020
How good are the dating methods? From what I read, they seem fairly reasonable, and they used at least two methods that give about the same dates. The question is not how old the cave is, but whether humans lived there and made the tools and charcoal.
What happened to the people? Part of the reason we think humans have been in the New World for only 15,000 years is not just evidence from habitation, but from DNA of Native Americans (note: there are some older estimates). If that’s the case, why doesn’t the DNA give a consistent age of 30,000 years from when Native Americans branches off from East Asians? One possibility is that the early arrivers went extinct without leaving descendants, so we wouldn’t find a genetic signature of their existence. Given that some paleoanthropologists see evidence of an early arrival from other sites, like that in the Yukon, the possibility of extinction seems unlikely.
All in all, this is an exciting finding, and may well be right, but we’ll have to let the experts fight it out.
Excavating in the cave, a photo from the Science precis:
h/t: Matthew Cobb
____________
Ardelean, C.F., Becerra-Valdivia, L., Pedersen, M.W. et al. 2020. Evidence of human occupation in Mexico around the Last Glacial Maximum. Nature (2020). https://doi.org/10.1038/s41586-020-2509-0
Oh, I don’t know, it still seems reasonable to me. 15,000 years may not be much in geologic time, but it’s plenty of time for a human group to discover the Americas, travel up and down the coast, live in the Americas in small groups for hundreds or thousands of years, and still go extinct before the second wave.
I find it hard to believe that a human group that could have colonized most or all of North and South America, presumably improving its use of technology and resources as it settled in, would slam-bam go extinct without some other group having come along and provided a “helping hand”.
The fast and larger second wave is a problem for a slow and small first wave, as is the lacking evidence of continuous gene flow in the latter case.
I always thought that the idea that there was only be one* migration from Asia to the Americas made no sense. Why wouldn’t people be going back and forth constantly? It’s not as though the first arrivals built a wall to keep everyone else out.
*Actually, two–the Inuit were later arrivals.
The book in 3. below says ‘at least 4 migrations”, agreeing with you.
There may be two Inuit migrations, too.
Because the genomes show nothing like that (on the largest scale).
“…the best guess was that humans crossed the Bering Strait from Siberia ABOUT 15,000 years ago, and then spread through the Americas.”
With a bit of an exception, the following agrees with this:
CH. 7, “In search of native American ancestors” of the ‘bible’ by David Reich about the ancient DNA work of the past decade or so, namely “Who we are and how we got here”
The exception is that it would say AT LEAST 15,000 years ago. I’ve not looked further at it to see if he conjectures a lot more or not.
I’d read it as soon as it came out (and suggested it here) and should make time to read it again soon.
Reich does essentially give credit to his wife Eugenie as a co-author.
Agree on David Reich’s book: Very good.
I am no paleontologist, but I have been seeing pictures of various stone tools for a long time. Unless someone can demonstrate otherwise, those artifacts do look like stone tools, especially the ones that look like spear points. The simpler forms, made from a small # of blows directed on both sides, can hardly be an accident as far as I am aware. I have certainly never seen rocks like these that were not regarded as stone tools.
There is no evidence of later, more delicate strikes to create a fine cutting edge, but nevertheless these types of artifacts still resemble those made from early Homo sapiens cultures.
We still need bones. Bones is what we need. And we need more extraordinary evidence to back up the extraordinary date.
The crude appearance of the stone tools could be due to the raw material. In many regions, suitable quality stone is not available. If only coarse-grained rocks are available, the stone tools will tend to be more crude. Flint is not available everywhere. Meltzer does raise a good point, asking why stone tools are not found more widely in the region if people occupied the area for a long time. But, they certainly do look to be genuine stone tools.
I agree they look very much like tools, not just geology. It would be helpful to see the edges up close to look at the points of fracture. In flinty materials it would show consistent multiple conchoidal fractures where pressure was used to chip off bits to shape and sharpen the rock. Not that it even needs to be precise and pretty. One can get a good sharp edge with a crude smash and discard the rock when it’s dull, then grab another one. You could do this either because you lack the skill for refined tool craft like in early human tools found in Africa, because the materials are plentiful, if you’re in a hurry, or probably a dozen other reasons. Even a flake that you chip off a proper tool can be used as a quick throw-away tool itself. Likewise, microscopic views of the edges of the rocks, if used by humans, would show wear patterns, scratches in fairly regular directions due to the cutting action, against bone for example. Geological wear on naturally broken rocks wouldn’t have this. But, caveat here, I am no expert, I only minored in anthropology, and that’s been 8 years ago, and I am not active in my local archeological society any more so take more than a grain of salt with that butchered mammoth…perhaps a better educated professional can agree, add to, or correct my post.
I have not looked at the articles (I should). If the rocks are a match to rocks in the immediate area, then that adds a bit to the possibility that these are somehow artifacts. Maybe rocks exfoliate out in these shapes? But paleontologists should not be fooled by that.
If they are not a match to rock sources in the area, then that would be strong evidence for human transport.
I won’t pay Nature to read the actual journal article but yesterday I read a different report about this which, if I’m not misremembering (or misunderstanding, either are possible) it said that the rock was not of a type naturally occurring in the cave, but I can’t recall if it could be found in the area. Perhaps someone with access could clear the fog from my limited memory on that.
I have personally found a place along the Osage river where it was clear
someone had sat there and manufactured tools and the debitage as mentioned by Nicholas K. was quite significant but only in a small area of a few square feet and looked very similar to the photo above. I’ve also found a beautiful but broken point a few hundred feet away up a broad ridge and a nice scraper not far away where my dad used to take me camping. Not that it has anything to do with the paper it was just neat to find. Also cool was the guy who recently found a well-preserved wooden bow, possibly 400 years old in a muddy creek in Mississippi. Three cheers for high-tannin water content and anoxic mud!
I would like to add here some more thoughts, but these are more toward this being a false positive – no human artifacts.
1. The comportment of the artifacts suggest a long occupation of the site, but…
2. The critique article mentions that there are various animal bones but no signs of butchery. One could say the absence of evidence is not evidence for absence, but doesn’t that really amount to evidence for absence this time? I would think the evidence of butchery should be there, along with other evidence of habitation like a fire hearth.
3. Those things that look like crude spear points are barely 3 cm long! The small scale bothers me. Well, maybe poor quality stone obligates humans to make arrowheads with whatever they have.
4. A speculation here. It would be very easy for the researchers to ignore what they are not looking for. Could they be recording rock fragments that happen to look like artifacts while ignoring other fragments that don’t?
If the alleged stone tools are exfoliated rock (which certainly is possible at high altitude, where freeze-thaw occurs), any trained archaeologist shold be able to recognize that. If the tools were manufacured on site, there would be debitage. If tools were not manufactured at the site, and there is little to no natural exfoliated rock fragments, then they are more likely tools. If there is a load of exfoliated rock and only a few putative tools, then it is less likely they are genuine tools.
“3. Those things that look like crude spear points are barely 3 cm long!”
Excellent point – no pun intended. Perhaps the people were very small. There’s precedent for that, even though this could be a hominin as we don’t know it. But what, precisely, a 3cm long sharp-ish stone could do in any case, is not clear.
I suppose I could read this paper – perhaps it’s in there.
I just had a look at some of the photos of the site — it is a large cave with tons of exfoliated rock all over. I am now having doubts (but I am notan expert on lithics). Some cut marks on bones would really help the case for human occupation. Those also seem to be lacking.
Mark, exactly what I was thinking: No butchery, no hearths, no human remains (not even a tooth), and the “tools” being selected from an enormous quantity of rock fragments. Also, I suspect that material identified as charcoal isn’t necessarily burned wood but may be derived from wood long buried under anaerobic conditions.
Burned wood is found naturally all the time. Humans didn’t invent fire. Now, find a hearth and we’re talking something different.
Good points!
I should read the paper through.
I would like fellow reader’s thought on this.
In reference to David Reich’s book, “Who We are and How We Got Here”, he discusses Population Y on pages 176-181 of the hardback book.
We find this sentence on page 177: “If there were ancient people on the continent who were displaced by First American, the may have mixed with the ancestors of present-day populations, leaving some statistical signal in the genomes of peole living today.”
My question: Could this be some evidence of that population Y?
The 3 or 4 pages you mention beyond 177 do take this “Population Y” very seriously. But it seems their evidence makes it unlikely to be anything like South Sea islanders coming across the south Pacific to establish themselves in South America.
For example from page 181: “Our estimate…is based on the assumption that Population Y traversed the entirety of Northeast Asia and America without mixing with other people it encountered..”.
Yes, that is my point…that Reich seems to imply, from my reading, that there may have been people in the Western Hemisphere before the “First Americans” or even “First Nations” or the “Indigenous”.
All of whom came from the area around Siberia…..
That would be genetic evidence, though. Unique molecular markers mixed in the DNA of some native American populations today. But those unique markers (if the markers exist) could have come from any recent but also extinct population of humans.
I think it is statistically pretty easy for populations to die out and leave no genetic trace that they even existed. They could mix with other populations before they die out, but if those other populations happen to die out too, then that is that.
Do your research, Jerry. North America was populated by the lost tribe of Israel.
That’s one of the things that Mormons are expected to believe, is it not?
Yes, it’s in the Book of Mormon, although the theory probably had non-Mormon adherents as well. I don’t really know much about it. I just thought it was an amusing follow-up to the “do your research” charge the wokes always lead with before accusing someone of cultural appropriation. We should create a whole new comedic genre based on phrase complements to “do your research” 🙂
Yes, I realized it was a joke of course; and I guess I vaguely thought this “lost tribe” idea had existed long before Josoph Smith.
Mormons are unlucky that their doctrines were invented just before archaeology and paleontology became proper sciences. Their evidence turned out to be against them.
I have a 2-volume book published in the 19th-century that says the Indians were Welsh [based on the similarities of some words].
Except the ones who drank a superior kind of beer. They were Cornish Gaelic descendants, or maybe Orkneyans, or Lettermullen island fishermen who got blown across the Atlantic in a storm??
It is very good that they managed to get two different dating systems to work in the same deposits, giving congruent results. That’s a major necessity for demonstrating a pre-Clovis occupation of the Americas.
It is very unfortunate that the putative artefacts are less convincing. I heard of the publication a couple of days ago from the dating community, who like two methods producing overlapping results in a stratigraphically secure context. But they never showed pictures of the putative artefacts. Wildly convincing, they are not. At the level of detail presented here – microwear might change that picture, but you’d have expected them to present that data.
Ho hum. Maybe the next site will have the perfect concatenation of evidence. Maybe not. Maybe the Clovis point-makers really were the first occupants of the Americas (though I personally doubt it – H.sapiens have had rafts and fishing for 50kyr+, and the Aleutians and Beringia have probably been productive seas for a very much longer time, so I would anticipate long periods of coastal exploration as the glaciers waxed and waned – which would make Clovis being the first settlement quite surprising. Whether the first settlers were genetically continuous with the “First Nations” is a separate question. Whether they left evidence of their activity which wasn’t overprinted by later occupation or buried below the rising seas … nobody knows. Yet.
Maybe this above was intended as a general comment, not a response to my corny (Cornwall?) beer joke.
Anyway something occurred to me that hadn’t before which is not unrelated to this one above:
If Beringia, the land now under the sea near the Bering Strait (plus some on either side), was partly occupied for several thousand years before any ‘concerted push’ into what’s now North America (the ‘concerted’ just a figure of speech), it may be that exactly when the first real settled people in America (not US necessarily!) came there is not very well defined. If an easternmost settlement was for centuries near the present Alaskan coast and varied back-and-forth, it doesn’t seem out of the question that a couple of thousand years difference in two claims about this could be equally correct/incorrect.
It’s not like Lief Erickson (formerly Christopher Columbus) just suddenly shows up at a very particular time.
Beringia is a pretty complex bit of seabed. A lot of the commentary on it seems to think of it as a sort of on-off switch. I dug out some bathymetry a while ago … where’d I put it … Meh, I put it “somewhere safe”, can’t find it now.
I re-did the presentation of the bathymetry. It’s at https://wellsite-geologist.blogspot.com/2020/07/beringia-bathymetry.html I can do higher resolution if you want, but the basic story of a belt of islands and mainland fringing the south side of the “land bridge” provides a more-or-less continuous environment from temperate zones to arctic ones which wouldn’t require technological leaps, rather evolutions. One does wonder almost why it took so long for humans to get to the Americas.
Thanks–interesting website.
From knowing the numerical details of ocean levels at various times, one could make maps of Beringia at those times, using these ocean floor levels and assuming that hadn’t changed much during the intervening time.
Hasty thoughts:
• I presume the composition of the stone objects match what would have been the available stone in the general area
• is the possibility of humans transporting the stone objects at a later date from Northern hemisphere sources ruled out? Or some other such scenario- local inhabitants given a collection that was hidden. This probably would have left traces of DNA, however.
One of these days, if the early date is correct, we will find some bones or other strong evidence. If it’s not correct, we will continue to find merely suggestive sites, forever. It’s hard to prove humans were not here then.
I see that Douglas Fir is mentioned.
Douglas Fir :
https://en.m.wikipedia.org/wiki/Douglas_fir
^^^distribution is only in Pacific Northwest
Mexican Douglas Fir :
https://en.m.wikipedia.org/wiki/Pseudotsuga_menziesii_var._lindleyana
… So I suppose the Mexican species is what was found…
When did people start putting holes in stone?
Stone – not so long ago (tens of kyr). Bone, antler, ivory – materials with higher tensile strength, probably a good deal longer. Wood – to quote the comedians Flanders & Swann, “We ‘ad a Wood’enge ‘ere once. But it rotted.”
Punching through stone isn’t that easy. The easiest way is to use a compound tool – a tough material like a dense wood, or antler acting on a hard material (sand ; emery, once you learn to identify it) to make a composite tool. That’s a sign of the neolithic and mesolithic rather than palaeolithic. Whether what we now understand as the easiest way was the first way … another good question. Got any other ideas how to do it, which would be compatible with Uggg the caveman (with a kayak tied up nearby)?
“Perforated shells found at South Africa’s Blombos Cave appear to have been strung as beads about 75,000 years ago”
Not stone, but kinda hard.
I remember a claim that those were parasite holes. But I have no source to that.
I.e. there was (is) a natural pick of shells that could be strung.
I see how that would work. It seems to me (no special expertise) it would be easy to tell the difference. As I recall, also pigments found which suggests they were decorating their bodies? Bead necklace, a touch of rouge, and I’m ready for a night on the town. 🙂
My archaeologist friends doubt that the stone objects are human artefacts. The items called flakes and points are found among lots and lots of other stone fragments that are not interpreted as flakes or points — there is a wide distribution of shapes and sizes of all these little bits of stone, some of which have shapes like stone tools. Instead of just seeing the items that the authors interpreted as points and flakes, I’d like to see them against the background of all the other similar-sized stone fragments (and I would like to know the relative frequencies of the flakes or points versus other non-tool fragments. The lack of such tools in sites with later dates between 30,000 and 15,000 years makes human occupation seem less likely. The absence of evidence of the use of the tools (butchered bones) is evidence of absence because such butchery is typically found alongside the discarded tools themselves at similar kinds of sites that also have other evidence of human habitation at later dates.
Also the authors engage in some unfortunate exaggeration. In the Abstract they write, “Here we present results of recent excavations at Chiquihuite Cave—a high-altitude site in central-northern Mexico—that corroborate previous findings in the Americas10,11,12,13,14,15,16,17of cultural evidence that dates to the Last Glacial Maximum (26,500–19,000 years ago)18, and which push back dates for human dispersal to the region possibly as early as 33,000–31,000 years ago.”. But those references 10-17 are all studies from much farther north and from much later dates, and extend the evidence for human occupancy only to about 16,000 years ago. Those other references don’t support the idea of earlier migration >30,000 years ago. So unfortunately I think this is just another case of the tabloids (Nature, Science, PNAS) betting on a result that might be important, and not caring too much if it might be instead just wrong.
I was wondering too, if these are artifacts, are they part of a wide field of similar stones, or are they localized to certain layers and areas of the cave where a human would sit and make blades? I didn’t read the paper. Curious hominins want to know.
good analysis, Mike
exactly what I was wondering
Were these “tools” perhaps cherry-picked from a great distribution of rock fragments generated by some natural process?
I am thinking of ordering a pile of crushed limestone from a local quarry, then pick through that pile to find all the hominin stone tools in that pile. Maybe I too can publish in Nature.
When I hear news like this, I always see what Razib Khan because he helps explain things in a manner that well educated layman can understand. Fortunately, he has a podcast about this on Insitome which will come out soon.
‘Talking to the author I am more than 50% convinced that humans were present in the New World 32,000 years ago, and 90% convinced they were here 25,000 years ago. This is well before what is needed and expected from the standard “Beringian standstill” model.’
His blog:
https://www.gnxp.com/WordPress/2020/07/23/how-the-amazonians-got-their-australasian/
The podcast:
https://insitome.libsyn.com/
This will go down as yet another poorly supported bit of pre-15000 evidence. We still await a well dated site with clear evidence of human activity. People really want to find older sites in the New World and, as old Richard Feynman said… “you are the easiest person to fool”.
Too bad one of them didn’t poop in the Mexican cave as someone did in the Paisley caves in Oregon.
https://advances.sciencemag.org/content/6/29/eaba6404
They’ll just need to look for the outhouse. Look for an inscription:
Some come to sit and think;
Others come to …..
“By poopular request …”
🙂 They were probably all pooped out after their long hike from Asia.
If this holds up, will it be the first known case of humans showing up in a region and *not* wiping out the local megafauna?
It has been established that the Aborigines have been in Australia for at least 50,000 years, so I think it entirely possible that humans have been in the new world for 25,000 years.
That is not a logical statement.
Yes, it’s odd. Humans have been in Asia for nearly 2 million years (erectus), but didn’t make it to the Americas.
Oops, that was in response to GBJames. And of course I mean that our human species was the first to get into North and South America, showing that it isn’t easy. Erectus _nearly_ made it to Australia, lots of island finds in between and even passed deep waters.
Was there not a land bridge from continental Asia to New Guinea to Australia at times when Erectus was already in Southeast Asia?
That’s a bit warmer than Beringia and Alaska, so better ape habitat.
If I remember correctly, H. erectus never inhabited the northern regions of Asia, from where it would have a realistic chance to reach the New World.
It is reasonable to think that any time the conditions allowed people to cross into the new World on foot, they likely would have done so.
There seems to be evidence that pre-human and later very early humans were occupying Siberia from more than 100K years ago.
I would go with the assumption that there were many incidents of small-scale migration during each of the periods where the land bridge was present, and the area on the western side was occupied. Even if Beringia provided less than ideal resources, people could be pushed in that direction by more dominant groups.
Proof of that happening at the earliest date is always something to look for, but it makes sense that it would happen many times, at least on a small scale.
The separation of the Americas from Asia is very old and blocked passage back and forth for many, many, species. Humans were just one of them. There simply is very little evidence for humans prior to about 15000 years ago. Archaeologists have been trying to find good evidence for earlier habitation for a long time and all that appears is this thin gruel. Meanwhile, in the old world, it is comparatively easy to find sites older than that.
This tells us something.
The Science criticism is a good find! The only problem I can think of is that the critics likely haven’t seen the source material, so that criticism of the stoon tools is like the evidence itself weak.
I said this yesterday in a comment in another WEIT thread on the find:
“I would add that, as the paper’s admit, there isn’t any genetic evidence (yet) either in Beringia or further south that such an early gene flow would have taken place. The current evidence, which has helped dethrone the Clovis first hypothesis, is of migration – likely along the kelp highway [ https://blog.education.nationalgeographic.org/2017/11/08/did-the-first-americans-take-a-ride-on-the-kelp-highway/ ] – ~ 17 – 20 kyrs from Beringia and quickly flooding the continents.”
“stoon tools” = stone tools.
You mean not stone spoons? (just kidding)