In 1977, Canadian archaeologist Jacques Cinq-Mars spent 10 years leading the excavation of a uniquely important site known as Bluefish Caves in Yukon, Canada. What he and his team discovered there eventually became what is today one of the most compelling chapters in the ongoing search for the first Americans………..
Cut-Marks in the Bones
The Bluefish Caves site consists of three karst (limestone) caves, located about 50 kilometers away from Old Crow village in northern Yukon. The Caves – like the HMS Terror site in Nunavut, and so many others – were already known to local First Nations members in the area. “The Vuntut Gwitchin [people] knew about the caves and visited the site many times,” says Lauriane Bourgeon, a researcher who has been studying ancient remains recovered from the caves. But it was the Cinq-Mars expedition that conducted the first archaeologically controlled investigation of the site, leading to the recovery of a wealth of faunal remains, including fish, birds, and mammals, as well as around 100 lithic artifacts, including microblades, cores, burins, small flakes, and other debris. When Cinq-Mars and his team radiocarbon dated the artifacts, the results were shocking: they appeared to be close to 25,000 years old.
This new evidence challenged the widely held theory that humans didn’t arrive in North America until much later. Not surprisingly, Cinq-Mars’ work was largely dismissed by much of the scientific community. That is, until decades later, when Université de Montréal’s Ariane Burke and Lauriane Bourgeon of the Hominin Dispersals Research Group (HDRG), and Dr. Thomas Higham, Deputy Director of Oxford University’s Radiocarbon Accelerator Unit, returned to study the faunal collections, now housed at the Canadian Museum of History.
One of their objectives was to re-determine radiocarbon dates for human activity at Bluefish Caves. The first step was to establish which bones were culturally modified, and which bones were marked as a result of natural processes. Since striations and breakages can be produced by rock abrasion, archaeologists must carefully and systematically identify cut-marks made by humans – and separate them from markings that merely seem like human activity, but can be explained by other events.
Misleading cut-marks are often produced by carnivores, for example, whose jaws can create bone breakage and flaking that resemble human attempts at marrow extraction. One way to tell these markings apart is by the presence of other pits and punctures scoring the surface, created by carnivore activity. The bones may also be accompanied by bits of digested bone, left behind from the carnivores that consumed it. One of the most distinctive features of carnivore activity is the U-shaped tooth marks they tend to score into the bones.
Researchers evaluated and recorded such tooth marks for every specimen – with carnivore activity as an alternate explanation, these markings could not be used as evidence for definitive human activity. Bones that appeared to have been damaged by weathering, as well as biological agents like rodent gnawing, were also removed from the group of potential human cut-marks. While it’s possible these other processes may have simply obscured relevant cultural modification, scientific inquiry mandates a greater degree of certainty in the data. Therefore, the researchers used a set of six criteria for each potential cut mark, to determine which ones could have been the result of human butchery.
Searching for evidence of human modification can often be like finding a needle in a haystack. In this case, a whopping 36,000 mammal bones were examined from the caves designated as Bluefish Caves I and II. While researchers determined that the vast majority of samples were the result of carnivore activity – wolves, lions, and foxes were among those responsible for the bone accumulation – both caves also contained human-modified bones. The team postulated that Canids used the caves for den sites in the spring and summer, and that human occupation at the caves was sporadic and brief.
Biological and natural geological processes can present an obstacle when identifying cut-marks. Of the specimens from Cave II, for example, root etching was discovered on over 70% of the bones. Root etching is caused by the excretion of humic acid from plant roots, which leaves dendritic grooves in the surface of the bone. In Cave I, the more significant problem was abrasion – this had caused damage to 57% of the bones.
Ultimately, the researchers were able to determine that fifteen samples were definitively modified by humans, and twenty more were considered “probable” examples of cultural modification. The activities documented by the cut-marks on the bones included skinning, dismembering, and defleshing. The species represented in the human-modified samples included horse, caribou, wapiti (elk), and possibly Dall sheep and bison, as well as a bird scapula.
Six of the cut-marked bone samples were selected for radiocarbon dating, and the results yielded dates ranging from 24,000 to 12,000 cal BP. The oldest specimen was a cut-marked horse mandible from Cave II – this evidence, along with a caribou pelvis (also from Cave II) confirms a human presence dating to 24,000 – 22,000 cal BP. The caribou bone showed signs of filleting, while markings on the horse mandible were consistent with the removal of the tongue. Previous analysis on one of the horse’s teeth had also showed that it was killed in spring or summer, indicating a human presence during the warmer seasons. These findings are significant because they suggest that humans were, at least sporadically, living in North America during the Last Glacial Maximum (or LGM) and not after, as previously thought.
The human presence at Bluefish Caves also spans over 10,000 years – the caves were used on several occasions (or more) during the frigid cold of the LGM (then the Pleistocene) and into the Holocene. Three bone specimens from Cave I were dated to between 22,000 and 15,000 cal BP: a horse humerus, a horse metatarsal, and a caribou metacarpal. The humerus and metacarpal show marks from filleting activity, and the metatarsal shows signs consistent with the stripping of tendons. The youngest specimen, dating to 12,000 cal BP, was an unidentified bone fragment with signs of filleting. While the species couldn’t be confidently identified, researchers suggested it could be a wapiti bone, since other cut-marked wapiti bones were discovered in the same cavity.
While root etching, scavenging, and other biological and natural processes likely destroyed much evidence of human activity, we nevertheless now have definitive proof of human occupation at Bluefish Caves. The absence of hearth features and other markers suggest that the caves were used seasonally, probably as short-term hunting sites. This is the case for several Beringian cave sites, including Alaskan examples like Lime Hills Cave, Lower Rampart Cave 1, and Trail Creek Caves. By dating the cut-marked bone specimens from Bluefish Caves, HDRG researchers have provided archaeological support for what is known as the “Beringian standstill hypothesis.”
Horse metatarsal from Cave I: Cut-marks from stone tools indicate possible tendon stripping. Image courtesy Lauriane Bourgeon, Ariane Burke, and Thomas Higham
Caribou metacarpal from Cave I: Cut-marks from stone tools indicate filleting. Image courtesy Lauriane Bourgeon, Ariane Burke, and Thomas Higham
Unknown long bone fragment from Cave I: Possibly Wapiti bone, cut-marks indicate filleting. Image courtesy Lauriane Bourgeon, Ariane Burke, and Thomas Higham
Caribou coaxal bone from Cave II: Cut-marks indicate filleting activity. Image courtesy Lauriane Bourgeon, Ariane Burke, and Thomas Higham
Horse mandible from Cave II: Cut-marks indicate removal of tongue with stone tool. Image courtesy Lauriane Bourgeon, Ariane Burke, and Thomas Higham
Horse humerus from Cave I: Cut-marks from stone tools indicate filleting. Image courtesy Lauriane Bourgeon, Ariane Burke, and Thomas Higham
The Standstill and the Earliest Americans
The standstill hypothesis proposed that a genetically isolated human population existed in Beringia, from at least 23,000 to 15,000 cal BP, before eventually spreading into North and South America after the LGM. While human activity had already been documented in Western Beringia, from Yana River sites dating to 32,000 cal BP, there was little evidence to support the theory from Eastern Beringia. That is, until Bluefish Caves, which now verifiably indicate that people were in Eastern Beringia by at least 24,000 cal BP, during the LGM.
According to the theory, Central Beringia would have been the primary habitation zone for a human population until it was submerged at the end of the Pleistocene. Even during the LGM, Central Beringia would have been habitable – with warmer, humid conditions and even occasional shrubs and trees, humans would have had access to both fuel and food. Rising sea levels would eventually push the population inland; unfortunately, this also means any evidence of human habitation in Central Beringia is likely destroyed, degraded, or still underwater.
It’s possible that Bluefish Caves was located at the eastern border of this population’s range. Seasonal hunting parties, venturing out of the core range and into the steppes of Eastern Beringia, would explain intermittent visits to sites like Bluefish Caves. This matches the data recovered, which indicates irregular human occupation over a long period of time. Researchers have proposed that the standstill population was fairly small – tens of thousands at the most – based on both archaeological and genetic evidence. After the LGM, as the climate improved, it’s believed that the population increased and caused new expansions into North America. Humans were still using Bluefish Caves, as documented by the cut-marked bones, but became reliant on different species (such as caribou, bison, and wapiti) since others, like the horse, had become extinct by about 14,000 cal BP.
Around this same time, the warming climate allowed an ice-free corridor to form between the Laurentide and Cordilleran ice sheets. Long since believed to be the route that humans took to migrate from Beringia down into North America, the corridor wouldn’t have been suitable for human travel until 13,000 or 12,500 cal BP. Many archaeologists now suggest that these early inhabitants of Beringia likely travelled down the Pacific coast instead, as early as 16,000 cal BP. Archaeological evidence supports this theory, showing that humans settled south of the ice sheets before the ice-free corridor formed.
Map of gene flow in and out of Beringia, according to human mitochondrial DNA haplogroups. Colors of the arrows correspond to approximate timing of the events and are decoded in the colored time bar. The initial peopling of Beringia (the region depicted in light yellow) was followed by a standstill after which the ancestors of the Native Americans spread swiftly all over the New World while some of the Beringian maternal lineages (C1a) spread westwards. More recent genetic exchange (shown in green) is manifested by back-migration of A2a into Siberia and the spread of D2a into north-eastern America that post-dated the initial peopling of the New World. Image and text: Erika Tamm, et al. Wikimedia Commons
Bluefish Caves is not only the oldest known human habitation site in North America – it was also used sporadically for over 10,000 years, and provides evidence of a potential “standstill” population in Beringia during the LGM. It appears that humans survived and subsisted off the land bridge for an extended period of time, creating a genetically distinct population, and only began to migrate when sea levels started rising. As the climate warmed up, more people were able to survive, creating a strain on resources and causing expansion into North America. It’s possible the standstill population travelled along a coastal route, leaving evidence south of the ice sheets. Or, some other seafaring group or groups may have travelled there first – leaving evidence at sites like Buttermilk Creek Complex in Texas and Monte Verde in Chile – and the standstill population followed the ice-free route later. Burke confirms there is “much speculation about possible coastal dispersals,” noting that “the discovery of very early Clovis sites in North America… occur too close to the presumed opening of the ice-sheets to explain their geographical distribution.” According to Burke, “more survey work will be necessary – both in Canada and in eastern Siberia – in order to find more material to support the standstill hypothesis.” Although the theory doesn’t directly address subsequent migration routes, if it can be further substantiated we will be one step closer to determining the settlement patterns of North America’s first humans.