Humans May Have Reached the Americas by 21,000 Years Ago, Genetic Study Suggests

Archaeologists have debated for more than a century whether humans first entered the Americas before, during or after the coldest peak of the last ice age, known as the Last Glacial Maximum (LGM). New research examining the available genetic evidence suggests that the populations that gave rise to today’s Indigenous peoples migrated to the Americas no later than 21,000 years ago.

“Evidence shows that the arrival of humans—the ancestors of modern Indigenous peoples—probably occurred near the end of the Last Glacial Maximum, although migration may have occurred earlier,” study co-authors Bethany Potter, an archaeologist with the Kansas Geological Survey, and Savannah Hay, a biological anthropologist at the University of Kansas, told Live Science in an email.

Three theories about the first Americans

According to a study published Sept. 23 in the online journal Current Views in Genetics and Embryology, researchers used genetic evidence to examine three major archaeological models for the origins of Native Americans:

• Pre-LGM migration: people entered the Americas more than 25,000 years ago.
• LGM migration: people arrived between 25,000 and 14,000 years ago.
• Post-LGM migration: people arrived after 14,000 years ago.

The debate is closely connected to the long-standing “Clovis first” theory, which once proposed that the Clovis people were the first inhabitants of the Americas. Archaeological discoveries have since challenged that idea, but researchers still disagree about which of the oldest sites are legitimate and how they should be interpreted.

“The reason this topic is so controversial among anthropologists is that not all archaeologists agree on which of the oldest sites are legitimate, which influences which models they think are the most accurate,” Potter and Hay said. “We know that humans were definitely present in the Americas by about 13,500 years ago. We still don’t know whether humans arrived earlier, and if so, how quickly.”

What ancient DNA reveals about migration

There is still relatively little genetic evidence from the first peoples of the Americas. The first complete genome from an ancient Indigenous person was sequenced in 2010. The individual lived in Greenland about 4,000 years ago.

Since then, scientists have published about 250 complete genomes and genome-wide data from approximately 1,200 ancient Indigenous people, according to the researchers.

These DNA studies have revealed important details about the population history of the Americas. During the LGM, about 25,000 years ago, groups living near Siberia or Beringia—the region that included the land bridge connecting Asia and Alaska—split into Ancient Native Americans, Ancient Beringians and one or more distinct groups.

Those populations then migrated rapidly along the Pacific coast, possibly splitting again into northern and southern Native American groups about 16,000 years ago. The genetic record also suggests the existence of separate, poorly understood “ghost” populations that have not yet been clearly identified.

“There are huge gaps in our genetic dataset,” Potter and Hay said.

For example, although the researchers’ group is based in the Great Plains, no ancient genomes from the Great Plains have yet been published. These geographic gaps may contain evidence of earlier migrations or previously unknown population movements.

Could people have arrived before the ice age’s peak?

Human footprints discovered at White Sands, New Mexico, have been dated to about 23,000 years ago. If that date is correct, it would mean people were living in the region before the LGM.

Acoma Pueblo people, who now live near the White Sands area, recognize the footprints as traces of their ancestors, Potter and Hay said.

However, genetic data from modern and ancient Indigenous peoples currently indicates that the White Sands population did not make a significant genetic contribution to the ancestry of today’s Indigenous peoples. The researchers noted that this does not rule out a connection entirely.

“It is possible that we have not sampled their descendant lineages, or that they contributed a low proportion of genetic ancestry to ancient North American populations,” the researchers said. “Maybe we just haven’t found any DNA from the White Sands residents yet.”

The oldest ancient genome linked to the first Americans

The oldest genome collected to date is from a 12,800-year-old individual known as the Anzick-1 child, whose bones were discovered in Montana.

DNA estimates from Anzick-1 and other early ancestors indicate that the first migration may have occurred about 21,000 years ago. The genetic evidence is therefore consistent with archaeological findings showing that people were in the Americas at least 14,000 years ago and possibly as far back as 21,000 years ago.

Still, several possible scenarios could explain how people entered the Americas before or during the LGM. More genetic data is needed to determine which model best fits the evidence.

More ancient DNA could solve the mystery

Expanding the geographic range of ancient DNA research could help fill major gaps in the record. However, Potter and Hay said many researchers are deliberately taking a slower approach to ancient DNA studies to ensure that research involving descendant communities is ethical and collaborative.

It remains unclear when—or whether—the long-standing question of when humans first entered the Americas will be definitively resolved. Current archaeological and genetic evidence does not point to a single answer.

Even so, the release of new ancient genomic data from the Americas could help researchers reconstruct how these early populations migrated and interacted over time.

How much do you know about the first people to reach the Americas? Find out with our information-packed My First American quiz!