Sometime between 23,000 and 21,000 years ago, human beings were in what is today New Mexico, according to a new report in the journal Science. If so, it is a dramatic development in our understanding of how the Americas were populated and would blow the "Clovis First" theory out of the water once and for all.
The basal theory of the occupation of the Americas is called Clovis First. It postulates that people only reached the New World about 13,000 years ago, and that the tools created by the Clovis people were the parent of all toolmaking technologies in the New World.
The Clovis First theory was already showing cracks. The new paper joins a growing body of research suggesting that occupation was earlier, by say a couple of thousand years. But in this case – if the footprints were dated correctly – humans would have already been in the Americas at the height of the Last Glacial Maximum, the peak of the last Ice Age.
Just this week, unrelated research revealed that the howling cold of the Ice Age did not deter early modern humans from exploring Eurasia. Evidently extreme cold couldn’t dampen early human wanderlust.
Roast seaweed and Clovis
It is generally agreed that people reached North America from Eurasia via the Beringia land-bridge, which linked the two continents when sea-levels were much lower because so much water was locked up in ice. Beringia was a vast grassland steppe. It didn’t snow there much, keeping it from becoming glaciated. Humans and other animals could and did walk across it.
How the ancient Eurasians advanced after crossing Beringia is another matter. They may have walked through gaps in the ice sheets, or braved the ice more directly. They may have sailed down the coast from Alaska to California and beyond. Or perhaps all of the above.
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The real question is when this happened. Whether they traveled over land or by sea, conditions during the Last Glacial Maximum would have rendered all these routes problematic. Evidence of pre-Clovis sites based on ostensible tool finds, or circumstantial evidence, has been treated with skepticism.
One example of such research, published in June in Latin American Antiquity, suggests that deer and rabbit bones found at the bottom of a Mexican rock shelter, Coxcatlan, date to around 30,000 years ago. The authors suggest that the animals may have been brought there by people. Or maybe the animals got there on their own, or were dragged by nonhuman predators that prefer to sup in rock-shelters, unmolested by aviating scavengers.
Another study, from 2020, reports on stone artifacts in Chiquihuite Cave near Mexico City that the authors claim indicate that the cave was occupied more than 30,000 years ago. Others argue that the artifacts were not tools, just rocks.
Another study of plant remains and environmental DNA in Chiquihuite found no traces of humans (which doesn’t prove they weren’t there), but did find bears.
Even if a stone is a tool, stones can be taken out of context, muddying up their time of deposition; and marks on seemingly butchered bones can be otherwise explained. While the very-old sites cause lips to purse, one site that may have more credence is MonteVerde in southern Chile. The site features hearths where seaweed was burned 14,000 years ago. That brought rise to a somewhat-pre-Clovis theory of occupation of the New World 16,000 to 15,000 years ago, which is quite widely accepted these days.
Now the footprints in New Mexico may change everything. No less than 61 human tracks were discovered in multiple stratigraphic layers, representing a span of about 2,000 years, when human beings were walking in what is today White Sands National Park.
The footprints were originally reported back in October, but at the time were only thought to be 10,000 years old.
Also, the footprints were found in situ, meaning they remained where they were laid down. So the question is: When were they laid down?
Crucially, the layers with the tracks were interbedded with seed layers, which could be carbon-dated. The results indicate that people were traipsing through the Americas at least 23,000 years ago, during the Last Glacial Maximum. “These data provide definitive evidence of human occupation of North America south of the Laurentide Ice Sheet during the LGM,” the authors state.
“Those tracks certainly look human; that part is compelling,” commented Prof. David Meltzer of Southern Methodist University, who was not involved in this research. “It would be great if they had come up with some artifacts to go with the footprints, both to supplement the case for a human presence, and to provide a glimpse of the associated material culture, [so] we might have a better idea of what to look for elsewhere of a human presence at this time.”
How secure is the timing of these prints? The authors themselves stress several caveats. The dating is based, as said, on radiocarbon-dating seeds, specifically of the aquatic plant Ruppia cirrhosa. But what the researchers call the “hard-water effect” could skew the results to the older side. Factoring in possible sources of error, they argue that major error beyond a few hundred years is improbable and conclude their dating is robust.
Meltzer doesn't disagree: “Even if the radiocarbon ages prove too old as a consequence of that effect, based on the stratigraphy I don’t think that the footprints will become that much younger,” he says.
So, 23,000 to 21,000 years, a time when the local climate was drying, people were walking around the paleolake Otero, which was perennial but would rise and fall based on changes in the local hydrological budget. If so, when is it plausible that their ancestors crossed Beringia?
“This would have needed to be when the ice sheets were melted, but also when sea levels were not too high to cover the Bering land bridge. This set of conditions may have occurred at around 30,000 years ago,” answers coauthor Sally Reynolds.
Fascinatingly, tracks of teens and children prevail while full-sized adult footprints were relatively rare. It could be that teens were sent to the lake to fetch water and their pesky kid siblings tagged along, as pesky kid siblings do, while the grown-ups were busy with skilled tasks, the archaeologists postulate.
For what it’s worth, in keeping with other paleo-people-prints, the paleo-walkers had relatively flat feet, as is common with the habitually unshod, the archaeologists explain.
Of mammoths and men
The human tracks had company: the researchers also found prints of mammoths, ground sloths, American camelids and other animals, at least some of which lived contemporaneously with the people.
Which brings the authors to their last point: the juxtaposition of tracks clearly show that people and now-extinct-megafauna coexisted in the Americas. They’re not the first to note that.
In South Dakota, a mother and baby mammoth were found from about 13,000 years ago near postulated stone tools, a find interpreted as potential evidence of butchering. In Michigan, a mammoth that may or may not also show hallmarks of butchering and was dated to 15,000 to 11,700 years ago. Paleo-Americans may have even immersed dead megafauna in lakes to preserve their flesh longer. There are other examples;
But did early arrivals to the New World kill off the North American megafauna? Maybe. Maybe not. Arguably in Eurasia and certainly in isolated spots of the world, we did; there is even a groundbreaking theory postulated by the team of Tel Aviv University’s Prof. Ran Barkai that archaic humans ate megafauna until there were no more, at which time their mental capacity had to improve in order to catch smaller and swifter prey, and as we continued to proliferate, we solved the problem by inventing animal husbandry in the Neolithic.
That doesn’t mean humans were key to the end of gigantic animals in the New World. Some believe climate changes were probably the chief culprit, with drastic drops in temperature around 13,000 years ago propelling their decline and extinction. Meltzer points to a paucity of evidence relevant to the megafaunal extinction: “Merely because humans were on the landscape with those animals at that time, assuming they were, is not evidence of a predator-prey relationship, especially in the absence of anything remotely resembling a kill site,” he says.
“The evidence is not clear that the megafauna were in decline. The White Sands research points to humans coexisting with megafauna for a longer time that previously though prior to the extinctions of these animals,” Reynolds explains. “It may be that a combination of warming climates and human hunting activities led to declining numbers of megafauna.”
But it does start to seem that as the megafauna of North America died off, we were there to watch it. Moreover, she says: if humans were in New Mexico that long ago, they had likely already become widespread; and other old sites will be identified.