Science1 publisher3 min readPublished
Genetic evidence puts the arrival of Indigenous Americans' ancestors at no earlier than 21,000 years ago
Kansas researchers say genetic evidence puts the arrival of today's Indigenous peoples' ancestors in the Americas no earlier than 21,000 years ago. That bound weighs against entry before the ice age's coldest peak, though the authors say gaps in sampling leave room for earlier groups.
The Scientist · Science desk
What happened
- Bethany Potter of the Kansas Geological Survey and Savannah Hay of the University of Kansas published the review online Sept. 23 in Current Opinion in Genetics & Development.
- Genomes indicate a population near Siberia or Beringia split around 25,000 years ago into ancient Native Americans, ancient Beringians and one or more "ghost" lineages.
- Scientists have published about 250 ancient Indigenous whole genomes, plus genome-wide data from about 1,200 ancient individuals, according to the review.
- Current genetic data show the people who left footprints at White Sands, New Mexico, made no significant genetic contribution to the ancestors of today's Indigenous peoples.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- constraint Anyone defending entry before 25,000 years ago now has to argue for people whose lineage left little in living Indigenous populations, because the ancestral floor sits at least 4,000 years later.
- contradiction If the White Sands date holds, the footprints predate the genetic floor by about 2,000 years, so either their makers' line is unsampled, it passed on little ancestry, or the date moves.
- exposure The floor is open to revision by each newly sampled region, so one ancient genome from an unsampled area could add a lineage that reopens the earlier-entry question.
The 21,000-year figure is a floor. The authors put their best estimate later. "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 told Live Science in an email [2]. The review weighed three archaeological models: entry before the LGM, more than 25,000 years ago; entry during it, between 25,000 and 14,000 years ago; and entry after 14,000 years ago, sometimes called Clovis First [4].
The date the pair treat as settled is later again. "We know that humans were definitely in the Americas by about 13,500 years ago. We still don't know if they arrived earlier than that and, if so, how much earlier," they said [6]. That leaves about 7,500 years between the genetic floor and the date they call definite [2]. Live Science's account describes the genetic data as lining up with archaeological evidence for entry at least 14,000 years ago and perhaps as far back as 21,000 [10]. Potter and Hay trace the long dispute to the sites. "The reason this topic is so contentious among anthropologists is because not all archaeologists agree about which of the earliest sites are legitimate, and that influences which model they think is most accurate," they said [5].
Genetic evidence of the first people in the Americas is scarce [17]. The field is also young: the first whole genome from an ancient Indigenous person, who lived about 4,000 years ago in Greenland, was sequenced in 2010 [7]. "There are huge gaps in our genetic dataset," Potter and Hay said. "For example, there are still no published ancient genomes from the Great Plains, despite that being where our lab group is situated." [11]
Human footprints at White Sands, New Mexico, have been dated to 23,000 years ago [12]. Live Science says that date, if correct, implies people were living there before the LGM [12]. On the review's own boundaries, 23,000 years ago falls inside the 25,000-to-14,000 window [4]. The Acoma Pueblo people who live in the region today recognize the footprints as traces of their ancestors, Potter and Hay said [14]. They offered two ways the genomes could miss that population. "However, it is possible we have not sampled their descendants' lineage, or that they contributed a low proportion of genetic ancestry to ancient North American populations," they said. "Perhaps we've just not found DNA from the White Sands population yet." [15]
I think the review supports a narrow conclusion. It concerns the lineage that has living descendants, and it is only as strong as the regional coverage of the genomes behind it [11]. The thing this doesn't tell you is whether other people arrived earlier and left no sampled line. The researchers wrote that several scenarios remain compatible with a pre-LGM entry [16].
What to watch
- The first published ancient genomes from the Great Plains, a region the authors say has none so far.
- Any ancient DNA that can be tied to the White Sands population or its descendants.
- Further dating of the White Sands footprints, since the reading of the site depends on the 23,000-year date being correct.