When did humans reach the Americas? The debate is fierce and the evidence controversial. One site in Brazil was particularly titillating: Pedra Furada, where researchers found evidence that stone tools were being used 50,000 to 32,000 years ago. And they were, dear reader, they were. The question is, by who?
Archaeologists have tended to assume that if one finds stone tools, or at least a lithic industry (a site where stone tools were manufactured), one has found a hominin site. That is because we, the epitome of evolution, are the only ones with the brainpower and coordination to make stone tools.
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But is it so? Well, sort of. Let’s put it this way: The theory that stone tool use necessarily attests to human presence is now debunked by a paper published in Sage Journals' The Holocene last week.
It isn’t that other species are known to make stone tools – meaning choosing a core and manipulating it to achieve a specific, planned end result. But Agustin Agnolin, Federico Agnolin and colleagues from CONICET (National Institute of Latin American Anthropology and Thought) show that capuchin monkeys are a clever lot and widely use stones as tools.
The sites where capuchins use stone hammers to crack nuts and for other uses end up looking remarkably like detritus in a site of early human lithic industry, they report.
Yes, the Agnolins and colleagues agree that Pedra Furada has stone tools that may date to as much as 50,000 years ago. However, they suggest they were used by delicate little capuchin monkeys, not great looming hairy humans. What archaeologists thought was stone spoor of human industry in Brazil tens of thousands of years ago was a capuchin lithic assemblage, they say.
They can’t prove as much, but they did prove that simians today are capable of producing evidence similar to that found at the archaeological site of Pedra Furada.
How? Capuchins are considered to be among the cleverest of the monkey set. But do they make stone tools, as the Homo lineage has been doing for about 3.3 million years at least? Or do they just bang rocks? How do we wind up with evidence interpreted as a stone tool-making industry? And what do capuchins do with their stone tools?
They do not make stone tools per se, says Agustin Agnolin in an interview. “Capuchins select rocks according to their size, but do not intentionally modify them before use,” he explains the crucial difference. “The modifications these rocks undergo is through their use as hammers or anvils, which leaves their surfaces with blow marks and occasionally fractures.”
There is one wrinkle, that also winds up producing “hominin evidence”: they also hit rocks together to crush their surfaces. “The monkeys lick the remains of crushed rock, possibly to incorporate minerals into their diet. This activity causes the rocks to split apart, but the remaining fragments are not used by the monkeys,” he says.
Got it. Capuchins are definitely one of the animals with the greatest variety of tool use, for a variety of tasks, but they apparently do not make stone tools in the sense of choosing a rock and knapping it.
Also, the stones the capuchins used to crack nuts or whatever are all sourced locally, within a few dozen meters at most, Agnolin says. Humankind has been known to travel pretty impressive distances for the appropriate stone, the researchers explain.
Teaching the kids
Agnolin and the team report on latter-day capuchins using stone tools today at Serra da Capivara National Park, just a few hundred meters from the purported site of ancient human activity. But tellingly, capuchins all over South America do this. There are multiple species of capuchin monkeys, and all have been seen using tools made of different materials in different places, Agnolin says - this is not some local artifact of behavior in one spot.
“In addition to the Serra da Capivara populations, they have been seen using stone tools in a nearby national park [Serra das Confusões] and in Chapada dos Veadeiros, which is about 800 kilometers [nearly 500 miles] as the crow flies from these sites – so it is quite widespread behavior in this species,” he explains.
One wonders: there is no question that the Homo lineage teaches the kiddos how to do things like make stone tools; archaeologists believe they have even found evidence for a “schools of rock” industry from 400,000 years ago in Israel. Do capuchins teach their young ’uns?
“As for whether they teach it to kiddos, their technology is not a genetically programmed behavior, so it must be passed between individuals,” Agnolin answers. “While adults are doing their tasks it is common for infants to be watching, so it seems likely that this is how they learn these behaviors. Currently there are primatologists working on the subject, so surely there will be news on this.”
Clovis, after all?
The “Clovis First” theory argues that the people associated with the “Clovis culture” were the first humans to reach the Americas, roughly 13,000 years ago. Or 14,000 years ago, Agnolin points out, based on evidence in Alaska. Anyway, “Clovis” is characterized by fluted stone tools and distinctive bone tools, and at this point there is zero solid evidence of human arrival below the ice sheet in the Americas at an earlier time.
With its stone tools, Pedra Furada is just one of several sites purporting to present pre-Clovis evidence. These include footprints in New Mexico ostensibly made 23,000 years ago; another footprint in Pilauco, Chile, about 13,000 years ago (all dates have margins of error and that footprint is anomalous in shape anyway); signs of human occupation in a Mexican cave about 30,000 years ago, and quite a bit more.
A statistical model of human dispersal factoring in genetic and climatic evidence suggests that humans likely reached the Americas before the Last Glacial Maximum, which was 26,000 years ago.
All the above are controversial: the footsteps are human but may have been misdated. And regarding some pre-Clovis early “stone tool” sites in the Americas, as one archaeologist snorted in conversation with Haaretz: either human beings went back 2 million years in time in technology or they were just rocks.
Let us be clear that real human sites from the Late Pleistocene, from 50,000 years ago and onward, tend to have hallmarks not found at Furada such as symbolic objects, cave art and that sort of thing; cut marks on bone and whatnot – none of which our monkeys produce. (Animal art is not a real thing.)
“Although we have not developed detailed comparisons with assemblages that we know were mainly made by humans during the Holocene (the last 10,000 years) in Serra da Capivara, we can say that they are very different from those made by monkeys and those supposedly made by humans prior to 20,000 years before the present,” Agnolin says. “The Holocene assemblages of the region show sophisticated stone tools, made partly of exotic raw materials and with more complex knapping methods.”
It is fun to think that if capuchins use stone tools today and were using them 50,000 years ago, there’s no reason they weren’t doing so 500,000 or 5 million year ago. “The ancestors of the capuchins have been in the region for possibly millions of years, so there could potentially be similar, extremely ancient, sites,” Agnolin agrees. Talk about monkeying with the archaeological record – though sheer crudeness of the “tools” may speak volumes.
“In some contexts, humans have made very crude tools. But for assemblages to consist primarily of hammered pebbles or fractured rocks is highly unusual, especially in the Americas [a late phase in human evolution],” Agnolin sums up.
In short, the new paper does not take a position on Clovis here or there; it merely points out that piles of stone attesting to tool usage as much as 50,000 years ago in Brazil were probably made by monkeys. So, said piles do not support pre-Clovis occupation of South America.
Does it end the debate? It does not. Agnolin personally feels that most of the evidence supposedly showing human presence in the Americas before the Last Glacial Maximum is ambiguous, though there is rather more for post-LGM and pre-Clovis settlement. The truth is out there – we just don't know what it is yet.