Genetic Study Suggests Indigenous Ancestors Arrived in Americas During Last Glacial Maximum

A comprehensive review of genetic data suggests that the ancestors of contemporary Indigenous peoples entered the Americas during the Last Glacial Maximum (LGM), the most intense period of the last ice age, rather than before it. Published online on September 23 in the journal Current Opinion in Genetics & Development, the study challenges long-standing debates regarding the timing of the first human migrations to the continent.

For over a century, archaeologists have disputed whether humans arrived prior to, during, or after the LGM, which peaked approximately 25,000 years ago. The new findings, led by Bethany Potter of the Kansas Geological Survey and Savannah Hay of the University of Kansas, indicate that the primary lineage leading to modern Indigenous populations likely migrated no earlier than 21,000 years ago.

“The evidence points to the arrival of humans ancestral to contemporary Indigenous peoples likely near the end of the Last Glacial Maximum, but earlier migrations may also have occurred,” Potter and Hay stated in an email to Live Science.

The researchers analyzed three primary archaeological models: pre-LGM entry before 25,000 years ago, LGM-era entry between 25,000 and 14,000 years ago, and post-LGM entry after 14,000 years ago, known as the Clovis First theory. While humans were definitively present in the Americas by approximately 13,500 years ago, the exact timing of their initial arrival remains a subject of contention due to disagreements over the validity of certain early archaeological sites.

The study relies on a growing body of genomic evidence. Since the sequencing of the first ancient Indigenous genome from Greenland in 2010, scientists have published roughly 250 whole genomes and genome-wide data from approximately 1,200 ancient individuals. These genetic records reveal that around 25,000 years ago, a population near Siberia or Beringia diverged into ancient Native Americans, ancient Beringians, and one or more unclassified “ghost” lineages. These groups rapidly moved along the Pacific coast, potentially splitting into Northern and Southern Native American lineages around 16,000 years ago.

However, the researchers acknowledged significant gaps in the current genetic dataset. Potter and Hay highlighted the absence of published ancient genomes from the Great Plains, a region central to their lab’s work, noting that these omissions could conceal evidence of earlier migrations.

At White Sands in New Mexico, human footprints dated to 23,000 years ago suggest human presence prior to the LGM. The Acoma Pueblo people, who inhabit the area today, view these prints as traces of their ancestors. Despite this archaeological evidence, genetic data indicates that the White Sands population did not make a substantial genetic contribution to the ancestors of modern Indigenous peoples. The authors suggested this might be because descendant lineages have not yet been sampled or because their genetic input was minimal.

Currently, the oldest sampled genome belongs to the 12,800-year-old Anzick-1 child, discovered in Montana. Extrapolations from this individual and other early ancestors support the conclusion that the initial migration occurred no earlier than 21,000 years ago. The researchers emphasized the need for ethical and collaborative expansion of geographic coverage in ancient DNA research to fully understand peopling events. While the question of exactly when the Americas were first inhabited may not be resolved immediately, new genomic data holds the potential to fill existing gaps and refine historical narratives.