RESEARCH ◥ sites show that people were present and suc- REVIEW SUMMARY cessfully occupying different areas of North and South America between ~15.5 and ~14 ka ago, thereby leading the way to a new understand- ANTHROPOLOGY ing of the first Americans. In the last 15 years, genetic information from Late Pleistocene exploration contemporary Indigenous Americans and the remains of ancient individuals from Asia and and settlement of the Americas the Americas has transformed our understand- ◥ ing of the ancestry of the ON OUR WEBSITE first Americans. Genetic by modern humans Read the full article studies first concentrated at http://dx.doi. on the analysis of mito- Michael R. Waters org/10.1126/ chondrial DNA, but in the science.aat5447 last decade, technological .................................................. breakthroughs have per- BACKGROUND: NorthandSouthAmerica radiocarbon date early sites and the belief that mitted the reconstruction of prehistoric ge- were the last continents populated by modern the ~13,000-year-old Clovis lanceolate fluted nomes. These genomic studies have conclusively humans. The timing of their arrival, the routes projectile points associated with mammoth re- shown that the first Americans were the result they took, their homeland of origin, and how mains represented the first people to enter the of ancestral east Asian and northern Eurasian they explored and settled diverse environ- continent. This view began to change with the admixture. This founder population made its Downloaded from ments filled with now-extinct animals have discovery of artifacts dating ~14.2 thousand years way to eastern Beringia and after additional been debated for over a century. Addressing (ka) ago at the Monte Verde site in southern population splits traveled south of the conti- these questions is key to understanding the Chile. This discovery signaled that people must nental ice sheets covering Canada sometime development of later prehistoric and contem- have been in the Americas before Clovis and between ~17.5 and ~14.6 ka ago. These genetic porary Indigenous cultures. that early sites should be present in other parts results agree with the emerging late Pleistocene of the Americas. Initially, many sites proposed archaeological record. http://science.sciencemag.org/ ADVANCES: The study of the first Americans to predate Clovis did not stand up to scrutiny, made slow but steady progress during the having issues with geological context, dating, or OUTLOOK: The key to learning more about 20th century. The first half of the century even the archaeological evidence itself. How- the first Americans is investigating archaeo- brought the realization that people had entered ever, the last 30 years have seen an increasing logical sites with solid geological contexts that the Americas at the end of the Pleistocene. The number of sites providing evidence of early are accurately dated. Only rigorously investi- second half of the century brought the ability to occupation that cannot be dismissed. These gated sites using the best practices of archeol- ogy, geoarchaeology, and geochronology will provide the primary and pivotal data to inter- pret the past. Analysis of biomolecules, includ- ing DNA, proteins, and lipids from these sites, will enhance environmental reconstructions on July 22, 2019 and archaeological interpretations. This will require time and patience because building archaeological knowledge is a slow process. Genetics is a powerful new tool that has al- ready broadly deciphered the origins and popu- lation history of the first Americans. Although the general outline of the ancestry of the In- digenous American genome will likely remain unchanged moving forward, recent genetic studies show even greater genetic complexity during the peopling process, especially once people were south of the ice sheets, and this storywillsurelychangedramaticallyand quickly with the generation of additional genomes. The ancestral history of the earliest peoples in the Americas will be realized as genetic knowledge from living populations and ancient individuals is combined with archaeological, geological, ethnographic, and oral records. This will require scientists and Indigenous peoples working as partners to 0 5cm uncover the past.▪ Page-Ladson site, Florida, ~14,550 years ago. Page-Ladson is the oldest radiocarbon-dated Email: [email protected] site in North America with artifacts of the first Americans, including a bifacial knife (inset), Cite this article as M. R. Waters, Science 365, eaat5447 found among the bones of extinct animals. (2019). DOI: 10.1126/science.aat5447 ART BY GREGORY A. HARLIN, NATIONAL GEOGRAPHIC IMAGE COLLECTION Waters, Science 365, 138 (2019) 12 July 2019 1of1 RESEARCH ◥ ancestral Indigenous Americans, but both popu- REVIEW lations maintained gene flow between them until at least ∼11.5 ka ago, which suggests their close geographic proximity (11). This branching ANTHROPOLOGY took place in either eastern Eurasia or Beringia (11). If the split occurred in eastern Eurasia, then these two lineages would have moved together Late Pleistocene exploration or sequentially into eastern Beringia as weakly structured populations (Fig. 1, A and B), main- and settlement of the Americas taining gene flow between themselves but not with Asian and Siberian populations. Alterna- by modern humans tively, the ancestral Indigenous American popu- lation could have entered eastern Beringia and then AB emerged (Fig. 1, C and D), ensuring Michael R. Waters gene flow between them but isolation from Asian or Siberian populations. North and South America were the last continents to be explored and settled by modern Sometime between ∼17.5 and ∼14.6 ka ago, humans at the end of the Pleistocene. Genetic data, derived from contemporary populations groups from the ancestral Indigenous American and ancient individuals, show that the first Americans originated from Asia and after population split into two branches: Northern several population splits moved south of the continental ice sheets that covered Canada Native Americans (NNA) and Southern Native sometime between ~17.5 and ~14.6 thousand years (ka) ago. Archaeological evidence Americans (SNA) (9, 11). The location of the shows that geographically dispersed populations lived successfully, using biface, blade, divergence of the NNA and SNA branches from Downloaded from and osseous technologies, in multiple places in North and South America between the ancestral Indigenous American population ~15.5 and ~14 ka ago. Regional archaeological complexes emerged by at least ~13 ka ago most likely occurred either while the groups were inNorthAmericaand~12.9kaagoinSouthAmerica. Current genetic and archaeological migrating south from Beringia or after they had data do not support an earlier (pre–17.5 ka ago) occupation of the Americas. entered unglaciated North America (Fig. 1, A and C) (9, 11, 13). This is based on the fact that he discovery of Folsom projectile points and Y-chromosome DNA lineages gave the first AB do not belong to either the NNA or SNA http://science.sciencemag.org/ with extinct bison and Clovis artifacts with genetic insights into Indigenous American pop- branches and are equally related to both, and mammoth remains in New Mexico, in the ulation history (6). These studies demonstrated because there was no gene flow between AB T first half of the 20th century, established that the ancestors of all contemporary Indige- andtheSNAandNNApopulations.Alterna- that people had entered the Americas at nous people had descended from only five mater- tively, the two branches may have diverged in the end of the Pleistocene (1). Since then, more nal lineages (haplogroups A, B, C, D, and X) and eastern Beringia and then these groups migrated Clovis sites were found and investigated, radio- two paternal lineages (haplogroups C and Q). south, but this would have required strong popu- carbon dating placed these sites between ∼13 These lineages also showed that the founding lation structure for thousands of years to pre- and ∼12.7 thousand years (ka) ago, and Clovis population came from Asia and experienced vent gene flow among the ancestral Indigenous became accepted as the oldest occupation in the a severe genetic bottleneck, in which a small Americans, AB, and the NNA and SNA groups Americas. For decades, archaeological sites pro- number of people with limited genetic diversity while in eastern Beringia (Fig. 1, C and D). posed to predate ~13 ka ago were rejected be- gave rise to all Indigenous people who occupied TheAmericaswerepopulatedbymembers on July 22, 2019 causetheylackedartifacts,geologicalcontext, the continent before European arrival. Further, of the SNA and NNA branches. These branches or secure dates—or had a combination of these mtDNA analyses suggested that the source pop- emerged sometime between ~17.5 and ~14.6 ka problems (2). However, over the past 30 years, ulation from which the first Americans were ago, placing a maximum limiting age on the archaeological investigations in both North and derived had been isolated from Asian lineages, peopling of the unglaciated lands south of the ice South America revealed occupations predating most likely in eastern Beringia, before they dis- sheets. Analysis of mitogenomes places the arrival Clovis that could not be dismissed (1, 3–5). In persed south. After this “Beringian Standstill” of humans into unglaciated America at ~16 ka tandem with these archaeological discoveries, (6), a small group fissioned from this isolated ago (14), and Y-chromosome