by JENNIFER RAFF
The debate over how people first arrived in the Western Hemisphere continues to roil archaeology in the United States – and to capture public attention. Today, the scientific community is contending with significant amounts of new genetic and archaeological data, and it can be overwhelming and even contradictory. These data are coming from new archaeological excavations but also from the application of newly developed tools to re-analyse prior sites and artefacts. They’re coming from newly sequenced genomes from ancient peoples and their contemporary descendants, but also from re-analysis of prior sequence data using new modelling tools. The generation of new data at times feels as though it’s outpacing efforts to integrate it into coherent and testable models.
Did humans first populate the Americas 100,000 years ago, 30,000 years ago, 15,000 years ago, or 13,000 years ago? Did they come by boat or by an overland route? Were the ancestors of Native Americans from one population or several? The answers to these questions would help us understand the grand story of human evolution. We know that the Americas were the last continents that anatomically modern Homo sapiens – humans like us – entered, but we don’t know exactly how this happened. These long-ago movements give us hints about the challenges ancient peoples across the world had to contend with during the Last Glacial Maximum (LGM), a prolonged period of coldness and aridity, when animals, plants and humans retreated to environmental ‘refugia’ for several thousand years. How did we survive this Ice Age? What technological and biological adaptations arose as the result of these environmental conditions? These questions capture the popular imagination and challenge the scientists working to uncover the details of individual lives thousands of years in the past.
To their Indigenous descendants, the stories we tell about these First Peoples of the Americas are highly relevant for additional reasons. Their deep ties and claims to the lands have often been ignored or expunged by governments, media and corporations across North and South America in order to make room for narratives that are more palatable, exciting or convenient to certain non-Native groups. The historical exclusion of Indigenous peoples from making decisions about research on their own ancestors and lands has caused significant harms to Native communities and individuals; when Native scientists and community members are full participants in the research process, the stories that emerge are not only more respectful but also more accurate.
Archaeological evidence establishes that Indigenous peoples were present in the Americas at least 15,000 years ago. Scientists don’t agree, however, on when people first arrived. Some archaeologists claim it must have been much, much farther back, citing evidence such as flaked stones in layers dating to ~30,000 years ago at the Chiquihuite Cave site in Mexico, bones with cut marks in layers dating to 34,000 years ago in Uruguay, flaked stones in layers dating to 30,000-50,000 years ago in Brazil, and even broken mastodon bones dating to 130,000 years ago in California. All of these claims are heavily disputed.
As a rule, an archaeological site won’t gain widespread acceptance as legitimate unless there is clear evidence of human activity, that evidence can be securely dated, and it is found in an undisturbed geological context. For example, a hearth containing the remains of charred animal bone fragments and stone tool fragments at the Dry Creek site in Eastern Beringia (near the present-day Denali National Park in Alaska) was dated to 13,485-13,365 years ago from wood charcoal pieces taken from within the hearth. The stone tools – resharpened blades, flakes, end scrapers, and the byproducts of manufacturing them – and repeated controlled fires used to cook animal bones clearly indicate a human presence. The intact stratigraphy and multiple independent radiocarbon dates from the hearth tell us when people were using this particular part of the site. To archaeologists, this is uncontroversial. In contrast to the Dry Creek site, there is no consensus that the very early sites discussed above have met that standard; critics argue that the stone ‘artefacts’ and ‘butchering’ marks could be the result of natural phenomena (or even, in some cases, left by modern construction equipment). There simply hasn’t been any uncontroversial physical evidence of a human presence in the Americas more than 15,500 years ago.
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