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The timing and effect of the earliest human arrivals in North America

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The peopling of the Americas marks a major expansion of humans across the planet. However, questions regarding the timing and mechanisms of this dispersal remain, and the previously accepted model (termed ‘Clovis-first’)—suggesting that the first inhabitants of the Americas were linked with the Clovis tradition, a complex marked by distinctive fluted lithic points¹—has been effectively refuted. Here we analyse chronometric data from 42 North American and Beringian archaeological sites using a Bayesian age modelling approach, and use the resulting chronological framework to elucidate spatiotemporal patterns of human dispersal. We then integrate these patterns with the available genetic and climatic evidence. The data obtained show that humans were probably present before, during and immediately after the Last Glacial Maximum (about 26.5–19 thousand years ago)2,3 but that more widespread occupation began during a period of abrupt warming, Greenland Interstadial 1 (about 14.7–12.9 thousand years before ad 2000)⁴. We also identify the near-synchronous commencement of Beringian, Clovis and Western Stemmed cultural traditions, and an overlap of each with the last dates for the appearance of 18 now-extinct faunal genera. Our analysis suggests that the widespread expansion of humans through North America was a key factor in the extinction of large terrestrial mammals.
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Nature | Vol 584 | 6 August 2020 | 93
Article
The timing and effect of the earliest human
arrivals in North America
Lorena Becerra-Valdivia1,2 ✉ & Thomas Higham1
The peopling of the Americas marks a major expansion of humans across the planet.
However, questions regarding the timing and mechanisms of this dispersal remain,
and the previously accepted model (termed ‘Clovis-rst’)—suggesting that the rst
inhabitants of the Americas were linked with the Clovis tradition, a complex marked
by distinctive uted lithic points1—has been eectively refuted. Here we analyse
chronometric data from 42North American and Beringian archaeological sites using
a Bayesian age modelling approach, and use the resulting chronological framework to
elucidate spatiotemporal patterns of human dispersal. We then integrate these
patterns with the available genetic and climatic evidence. The data obtained show
that humans were probably present before, during and immediately after the Last
Glacial Maximum (about 26.5–19thousand years ago)2,3 but that more widespread
occupation began during a period of abrupt warming, Greenland Interstadial1 (about
14.7–12.9thousand years before 2000)4. We also identify the near-synchronous
commencement of Beringian, Clovis and Western Stemmed cultural traditions, and
an overlap of each with the last dates for the appearance of 18now-extinct faunal
genera. Our analysis suggests that the widespread expansion of humans through
North America was a key factor in the extinction of large terrestrial mammals.
Until recently, the prevailing paradigm1 for the initial dispersal of
humans into the Americas held that the first Americanindividuals
were big-game hunters who entered the continent about 13thousand
years ago (ka) from Asia via Beringia, moving southwards through an
ice-free corridor between the Laurentide and Cordilleran Ice Sheets.
This paradigm proposed that, once below the 48th parallel north,
these human groups developed a material tradition (named Clovis)
that spread across North America, and which dates to between 13,250
and 12,800calibrated years before present (1950) (cal. )
5
. This
narrative, known as the ‘Clovis-first’ model, was widely accepted for
most of the twentieth century as it effectively answered most of the
questions associated with the peopling of the Americas—when, why
and from where
1
. However, the Clovis-first model has been refuted
by new archaeological and chronometric data
6–8
that demonstrate
the existence of sites that predate Clovis (often termed ‘pre-Clovis’
or ‘older-than-Clovis’6,9) as well as of distinct technological industries
that occur coevally1014. An earlier dispersal route along the Pacific
Coast is currently considered the most likely means by which people
moved into the Americas15,16, although this not universally accepted17.
To understand the pattern of initial human dispersals in a more
refined manner, we have used Bayesian statistical methods to analyse
chronometric data from a large number of North American and Ber-
ingian archaeological sites. Our results enable us to propose a new
chronology-based model for the peopling of North America.
We built high-precision chronometric models using Bayesian age
modelling on the OxCal 4.3 platform
18,19
on the basis of archaeological
and chronometric information obtained from 42archaeological sites
(Supplementary Information, Supplementary Table1). This approach
enables the incorporation of absolute chronometric data (in this case,
radiocarbon and luminescence ages) with stratigraphic and other rela-
tive age information (Methods). The sites we have analysed include
cultural components that fall, according to the literature, within one
of three technological traditions (Clovis, Western Stemmed or Bering-
ian) (Supplementary Information) or—as defined here—two exclusively
temporal categories (pre-Clovis and ‘Clovis-coeval’) (Fig.1). We gener-
ated probability density functions that correspond to temporal start
boundaries or age estimates for each site and tradition from the models
(Methods, Supplementary Information, Supplementary Table2), which
are reported below at a 95.4% confidence or credible interval. We also
used kernel density estimate methods, which estimate the underlying
distribution of a dataset, to visualize the spatial and temporal distribu-
tion of the data (Methods). We used the Greenland ice-core timescale
(GICC05)20 to place our results in the context of past climatic changes,
particularly the period that comprises Greenland Interstadial1 (GI-1)
and Greenland Stadial1 (GS-1)—beginning at about 14.7thousand years
before 2000 and ending at about 11.7thousand years before 
20004 (Figs.2,3). Although GICC05 and the current radiocarbon dat-
ing calibration curve (IntCal13
21
) are not synchronous, between 14,000
and 11,000cal.  the estimated offset is less than around 50years
22
.
Given the temporal resolution of this study, the effect of this offset is
therefore negligible.
Modelled start boundaries for pre-Clovis sites show the earli-
est evidence for cultural occupation in stratigraphic componentC
of Chiquihuite Cave (Mexico) at 33,150–31,405cal. , before the
https://doi.org/10.1038/s41586-020-2491-6
Received: 17 October 2019
Accepted: 26 May 2020
Published online: 22 July 2020
Check for updates
1Oxford Radiocarbon Accelerator Unit, Research Laboratory for Archaeology and History of Art, University of Oxford, Oxford, UK. 2Chronos 14C-Cycle Facility, SSEAU, University of New
South Wales, Sydney, New South Wales, Australia. e-mail: l.becerravaldivia@unsw.edu.au
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... In contrast with the other continents, the Americas have been mostly free of human influence until as recently as 13-20 k years BP (Barnosky and Lindsey, 2010;Becerra-Valdivia and Higham, 2020). Pre-human conditions, however, were very different from present ones. ...
... This reference (since ∼11 K years BP; Svenning and Faurby, 2017) assumes a climate relatively similar to the present and landscapes without permanent human settlements. These ecosystems, however, were significantly affected by mobile and widespread human hunter-gatherers which adopted fire to modify landscapes and contributed to the extinction of c. 80% of medium and large mammals (Becerra-Valdivia and Higham, 2020;Pinter et al., 2011). With pre-agriculture humans as top predators, main vegetation disturbance agents, and drivers of species redistribution, it would be ironic to take this condition as a reference for biodiversity conservation. ...
... Start boundaries were then modeled for this 'phase of priors' to determine an overall start boundary for peach introduction into the Oconee Valley. This method has recently been used by others to estimate age ranges for regional archeological traditions and cultures (e.g., 55,[66][67][68]. ...
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... Both scenarios typically assume the LGM is a temporal (and environmental) boundary for the preservation of archaeological materials, if not viability of movement into North America. Additionally, while many researchers have been open to the possibility of pre-LGM evidence (e.g., Madsen 2004), the proposed sites so far (e.g., Ardelean et al. 2020;Becerra-Valdivia and Higham 2020;Bennett et al. 2021;Holen et al. 2017;Rowe et al. 2022) are characterized by weak or controversial evidence, and have therefore failed to be widely accepted and seriously incorporated into understandings of peopling of the continent (e.g., Potter et al. 2022;Tune et al. 2018; but see Gruhn 2023). ...
... In the Old World, many sites have small lithic points, likely made to fire from projectile weapons such as spearthrowers and bows (Langley et al., 2020;Lombard and Phillipson, 2010;Metz et al., 2023;Sano, 2016;Wedage et al., 2019; see compilation in (Lombard and Shea, 2021, Table 1). In the Americas, there is evidence of human presence during the Last Glacial Maximum, but widespread occupation began after 15,000 cal BP in North and South America (Becerra-Valdivia and Higham, 2020;Prates et al., 2020). Early hunters made lithics for spears and probably spearthrowers (Gore and Graf, 2018;Hutching, 2015), but not the bow. ...
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