Make Out-of-America Great Again: Humans in the New World at 24,000 YBP
PLoS ONE 12(1): e0169486. doi:10.1371/journal.pone.0169486
Earliest Human Presence in North America Dated to the Last Glacial Maximum: New Radiocarbon Dates from Bluefish Caves, Canada
Burgeon, Lauriane, Ariane Burke, and Thomas Higham
The timing of the first entry of humans into North America is still hotly debated within the scientific community. Excavations conducted at Bluefish Caves (Yukon Territory) from 1977 to 1987 yielded a series of radiocarbon dates that led archaeologists to propose that the initial dispersal of human groups into Eastern Beringia (Alaska and the Yukon Territory) occurred during the Last Glacial Maximum (LGM). This hypothesis proved highly controversial in the absence of other sites of similar age and concerns about the stratigraphy and anthropogenic signature of the bone assemblages that yielded the dates. The weight of the available archaeological evidence suggests that the first peopling of North America occurred ca. 14,000 cal BP (calibrated years Before Present), i.e., well after the LGM. Here, we report new AMS radiocarbon dates obtained on cut-marked bone samples identified during a comprehensive taphonomic analysis of the Bluefish Caves fauna. Our results demonstrate that humans occupied the site as early as 24,000 cal BP (19,650 ± 130 14C BP). In addition to proving that Bluefish Caves is the oldest known archaeological site in North America, the results offer archaeological support for the “Beringian standstill hypothesis”, which proposes that a genetically isolated human population persisted in Beringia during the LGM and dispersed from there to North and South America during the post-LGM period.
As science moves into 2017, the proponents of the early peopling of the Americas are jubilating again. It used to be that the professional integrity of a New World archaeologist was achieved by making claims such as “dozens, even scores of sites failed to withstand critical scrutiny” (Meltzer, David. First Peoples in a New World: Colonizing Ice Age America. Berkeley: University of California Press, 2009, p. 11). Geneticists were calibrating their molecular clock by the “secure” dates of the peopling of the Americas furnished to them by archaeologists who attributed the founding migration of Paleoindians from East Asia to the emergence of Clovis culture in North America some 13,000 years ago. Students of world mythology were imagining how Asian myths traveled with people down the putative ice-free corridor into the southern parts of North America.
Then, the academic ice suddenly started to melt. Monte Verde, Buttermilk Creek, Paisley Caves, Page-Ladson and Monte Verde again (Dillehay, T. et al. “New Archaeological Evidence for an Early Human Presence at Monte Verde, Chile.” PLoS ONE 10(12): e0145471) – all documented the presence of humans in the New World prior to the Clovis times. The ice-free corridor turned out to have been biologically unviable for passing until several hundred years after Clovis (Pedersen, M. W. et al. “Postglacial viability and colonization in North America’s ice-free corridor.” Nature 537 (2016): 45-9). Most importantly, Amerindian genes were detected at the Mal’ta site in Western Siberia as early as 24,000 YBP. Finally, ground-breaking and paradigm-changing archaeological and paleobiological evidence is sometimes so fragmentary (a finger and a tooth in the case of the Denisovan site) that it takes long time and brand-new technologies to actually recover it.
The skeptical community quickly regrouped and argued that Mal’ta DNA (MA-1) documented not the migration of ancient Amerindians into Asia, but the moment when genetic proto-Amerindians began to segregate from one of their Old World antecedents. This is because there were supposedly no archaeological sites in North America as old as Mal’ta. And archaeology has established it beyond reasonable doubt.
Well, this out-of-archaeology logic was again flawed. Burgeon et al. (2016) have just furnished evidence that humans were present in the New World at exactly the same time as Mal’ta. Bluefish Caves in the northern Yukon Territory (Canada) was excavated from 1977 to 1987 by Jacques Cinq-Mars’s team. They claimed to have found evidence for cultural modification of animal and bird bones. Buergeon et al. (2016) confirmed and expanded their findings.
“We recorded a total of fifteen bone samples with cultural modifications confidently attributable to human activities (N = 10 in Cave I and N = 5 in Cave II), based on morphological and morphometrical criteria, and twenty more samples with “probable” cultural modifications for a total of less than 1% of the faunal remains… Different activities are attested including skinning, dismembering and defleshing. Cut marks were observed on horse (Equus lambei), caribou (Rangifer tarandus), wapiti (Cervus elaphus), and possibly Dall sheep (Ovis dalli) and bison (Bison priscus), and include a previously published bird scapula.”
There can be little doubt about the antiquity of these cut marks and about their human origin.
“It is highly unlikely that the cut marks observed on the Bluefish Caves faunal material were generated by nonhuman agents or natural processes. In Cave II, the horse mandible (J7.8.17) and a caribou pelvis (I5.6.5) date the human presence to the LGM, ca. 24–22,000 cal BP. The traces identified on these bones are clearly not the result of climatoedaphic factors or carnivore activity. The presence of multiple, straight and parallel marks with internal microstriations observed on both specimens eliminates carnivores as potential agents. The relatively high breadth ratio (12 and 18 μm, respectively), as well as the depth (91 and 95 μm, respectively) and opening angle (144 and 139 μm, respectively) that we measured are in the range of marks produced by stone tools reported by experimental and archaeological studies; the breadth ratio also differs from marks produced by carnivore teeth. Sedimentary abrasion or trampling are also eliminated since the caribou coxal bone shows no other signs of abrasion and the long, parallel striae on the horse mandible are simply too regular. Furthermore, the anatomical location and orientation of the marks are consistent with filleting marks in the case of the caribou bone, while the presence of multiple cut marks on the medial side of the horse mandible indicates the removal of the tongue. Previous cementochronological analysis of one of the teeth from this mandible indicated that the animal was killed in spring/summer, thus suggesting a human presence in Cave II during the warm season.”
Interestingly, the paucity of the specimens with cut mark at the Bluefish Caves site is not the reason to doubt the veracity of the site. In fact, it reflects objective cultural and climatic realities.
“The small percentage of cut-marked bones at Bluefish Caves I and II is not surprising. Our taphonomic analysis suggests that natural processes, particularly root etching and scavenging activities, may have destroyed some of the evidence of human activity. In other Beringian archaeological sites dated to the Late Pleistocene/Early Holocene, taphonomic studies show that cut marks are scarce (less than 1%) or even absent in bone assemblages highly affected by natural processes.”
This is strikingly similar to the Monte Verde II situation: ancient Amerindian cultural signatures were associated with highly perishable organic materials.
Another tantalizing tidbit of information:
“Furthermore, the Bluefish Caves, like other Beringian cave sites, were probably only used occasionally as short-term hunting sites. Thus, they differ from the open-air sites of the Tanana valley in interior Alaska and the Little John site in the Yukon Territory, where hearth features, large lithic collections, bone tools and animal butchery have been identified, reflecting different cultural activities and a relatively longer-term, seasonal occupation.”
This could reflect seasonality but the frequency of cut marks could also mean that at 24,000 YBP human populations in those latitudes were chronically small and diffused. And this fits nicely with molecular evidence for low heterozygosity and high Fst among Amerindians. Considering that such East Eurasian hominin populations with Mid-Pleistocene roots as Neandertals and Denisovans – a potential source for modern humans under the out-of-America II hypothesis – were even more genetically homogeneous than contemporary Amerindians, the Amerindian demographic profile may not represent an outcome of a random recent bottleneck (as the Clovis archaeological horizon would have it) but a more ancient and systemic demographic reality.
Burgeon et al. (2016) believe that the Bluefish Caves site supports the Beringian Standstill hypothesis. It’s unlikely, however, that a single find can support any specific scenario. The Bluefish Caves site’s impact is deeper than that. What it does prove is that 1) humans were in the New World as early as 24,000 YBP, which means no later than the earliest molecular signs of Amerindians detected in the Old World (MA-1); 2) archaeological evidence for older and older sites in America grows with time; 3) archaeology is a moving target as far as establishing the earliest horizons of human habitation in a particular area of the world; 4) the older the site in America the harder it is and the longer it takes to isolate cultural signatures because those signatures are found on perishable materials used by small, highly mobile and isolated populations.