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We still don't know how humans got to the Americas. Many researchers are arguing we need to ditch the land-first hypothesis of human migration, and look for underwater evidence of a seafaring past. It's an idea that's gaining momentum, though the evidence is complex and the proposal isn't unanimously accepted.

Expand chart

Data: Sites compiled from academic papers & information provided by Braje; Map: Lazaro Gamio / Axios

This map shows some of the oldest archaeological sites in the Americas. Many in South America are either along the coastline or major waterways, supporting the coastal migration hypothesis. But North America looks a lot messier and lacks coastal sites.

Why it matters: "We're trying to answer one of the most fundamentally important questions in American archaeology," Todd Braje, an author of the paper that appears today in Science, tells Axios. Recent finds have challenged the old, accepted models of a single migration over a single route.

The history of America used to be obvious: during the Ice Age, sea levels dropped and humans crossed a land bridge between Russia and Alaska. From there, they supposedly followed massive animal migrations down a narrow, ice-free corridor that eventually took them all the way to South America.

The mystery: Most evidence indicates the ice-free corridor opened between 13,500 and 15,000 years ago. But scientists have found a handful of archaeological sites in South America that are around 14,500 years old — and some disputed sites that may be thousands of years older — leaving little time for human migration across two continents to happen. Major finds include:

A solution? Braje and his collaborators make the case that early humans instead moved rapidly along shorelines, following a 'kelp highway' of food-filled fisheries. Crossing land means travel over difficult and varied terrain. Following the coast by boat may have been simpler.

Yes, but archaeologist Gary Haynes, who wasn't involved in the study, isn't convinced, "There is still a possibility the interior route was open to recolonizing animals, pioneering humans, and migrating waterfowl early enough to account for the first human presence in the Americas," he says.

Braje and his colleagues are the first to admit crucial data for the kelp highway are missing. There are very few archaeological sites along the North America coast. And, any coastal settlements that did exist are likely underwater because sea levels rose when the Ice Age ended.

"Archeologists have spent decades looking for early sites which are now inundated on the Pacific side of the continents," says Haynes. "I wish they'd find one, so we'd finally have empirical evidence." Braje and his collaborators have expeditions currently planned.

Go deeper: The above map outlines Clovis-associated sites with a black circle. For a long time, archaeologists believed the Clovis people, who appear to share a culture, were the first humans in the Americas. We now know that many archaeological sites predate Clovis. Still, Clovis settlements appear to follow the ice-free corridor, so some suspect they, at least, migrated on land. However, the 15,500 year old Friedkin site in Texas shows stone tools that, although they are not precisely Clovis, do share some characteristics with the later tech. This has led some to suggest that Clovis culture arose near Texas and spread from there. It's also possible that multiple groups independently invented the tools through a natural progression of trial and error.

Get philosophical: Sometimes new discoveries can raise more questions than they answer. It's very possible neither idea is correct — or that both are. "We now know less of the answer than we did 20 years ago," says Braje — and that's a good thing.

Go deeper

Updated 2 hours ago - Energy & Environment

Thousands without power as "hazardous" winter storm lashes East Coast

Satellite imagery of the Northeastern U.S. taken by NOAA on Jan. 17. Photo: NOAA

A major winter storm lashed much of the East Coast Sunday and Monday, causing widespread power outages and disrupting travel over the holiday weekend.

The latest: Authorities in North Carolina confirmed that two people died in a car crash and that they responded 600 vehicle accidents during the storm on Sunday, per the Washington Post.

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CDC director says COVID-19 messaging should have been clearer

Rochelle Walensky. Photo: Stefani Reynolds-Pool/Getty Images

Rochelle Walensky, director of the Centers for Disease Control and Prevention, said in an interview with the Wall Street Journal that the messaging around the COVID-19 pandemic and changing guidance should have been clearer.

State of play: Walensky is being coached by media experts and is planning to have more press briefings by herself in order to ensure that CDC is seen as an independent, scientific entity, rather than as a political one, the Journal reports.

3 hours ago - World

UAE asks U.S. to reinstate Houthi terrorist designation after attack

Secretary of State Tony Blinken (left) listens to United Arab Emirates Foreign Minister Sheikh Abdullah bin Zayed al-Nahyan during a joint news conference at the State Department iin October. Photo: Andrew Harnik/Pool/AFP via Getty Images

Emirati Foreign Minister Abdullah Bin Zayed asked Secretary of State Tony Blinken in a phone call Monday to re-designate the Houthi rebels in Yemen as a terrorist organization, a senior Emirati official told Axios.

Why it matters: Less than a month after he assumed office, President Biden rolled back the Trump administration’s decision to make the designation. He said it hampered humanitarian assistance to the Yemeni people. Since then, the Houthis have escalated their attacks against Saudi Arabia and other countries in the region — including an attack Monday in Abu Dhabi.