Ancient DNA Reveals First Americans

Researchers led by Bethany Potter at the University of Kansas reviewed published research to reevaluate the three main migration models. These models propose that the ancestors of today's Indigenous Americans arrived before, during, or after the Last Glacial Maximum.

The team examined findings from ancient DNA, archaeological sites, and environmental data to test the three scenarios. They found that the evidence best fits a timeline of 14,000 to 20,000 years ago for the arrival of the first people in the Americas.

Arriving after 14,000 years ago is at odds with most genetic evidence, which shows that key population lineages split well before a land path through the ice opened up. The authors argue this makes it more likely that people had already entered the Americas by this point.

The researchers also found that arriving before 25,000 years ago runs into problems, as current genomic data show no population splits stretching that far back. Any groups living in the Americas back then may have left no descendants today, or scientists may just not have found their DNA yet.

Proposed dates for the arrival of the first humans in the Americas span more than 100,000 years, with some sites suggesting human activity as far back as 130,000 years ago. However, the review's authors argue that genetics makes sites older than 25,000 years hard to fit and points to an arrival before roughly 15,000 years ago.

The study's findings are based on a review of published research, including archaeological sites such as Cerutti in California and Swan Point in Alaska. The authors ranked American sites by how much controversy they attract, with Cerutti and other sites being among the most disputed.

The researchers' approach was to sort the archaeological hypotheses into three models, according to how each relates to the Last Glacial Maximum. They then asked what genetics would be expected to show for each model, and found that the evidence best fits a timeline of 14,000 to 20,000 years ago.