Peopling of the Americas: How the First People Reached America

The peopling of the Americas is the story of how humans first reached North and South America, the last continents apart from Antarctica to be settled. Their ancestors came from north-east Asia, crossing through Beringia, the Ice Age land bridge between Siberia and Alaska. For most of the 20th century scientists believed this happened about 13,000 years ago, but new discoveries and ancient DNA now show that people were in the Americas by at least 16,000 years ago, and probably by 23,000 to 21,000 years ago.

Where the first Americans came from

From the 16th century onwards, European scholars speculated about the origins of the peoples of the Americas. In 1590 the Jesuit José de Acosta proposed that they had come overland from Asia, an idea broadly confirmed by modern science.

Genetic studies have clarified the picture. The ancestors of Native Americans formed from a mixture of two populations: an East Asian group and the Ancient North Eurasians, a Siberian people known from the genome of a boy buried at Mal’ta near Lake Baikal about 24,000 years ago. This mixed ancestral population then became isolated from other Asians, probably for several thousand years, a period known as the Beringian standstill.

The place of that isolation is debated, but Beringia was then a huge, unglaciated plain joining Asia and America, with sea levels some 120 metres lower than today. It offered grassland and tundra full of game and, in places, sheltered pockets of shrub and woodland.

The barrier of the ice and the routes south

South of Beringia lay a formidable obstacle. During the Last Glacial Maximum, about 26,000 to 19,000 years ago, two great ice sheets covered most of Canada: the Laurentide ice sheet in the east and the Cordilleran ice sheet over the western mountains. Where they met, they formed an almost continuous wall of ice from the Pacific to the Atlantic.

For people to move south, they had either to travel along the Pacific coast or wait for a gap to open between the ice sheets. Which route they took, and when, remains one of the central questions in American prehistory.

The ice-free corridor

For much of the 20th century the favoured route was an ice-free corridor that opened between the Laurentide and Cordilleran ice sheets, running from the Yukon to the plains east of the Rocky Mountains. Recent dating suggests that this corridor became physically open only around 14,000 to 13,000 years ago, and that it could support enough plants and animals for people to travel through it only somewhat later. That is too late for the earliest known sites further south.

The Pacific coastal route

Many researchers now favour a coastal route. Parts of the Pacific coast of Alaska and British Columbia became free of ice by about 17,000 to 16,000 years ago. People could have moved south along the shore, perhaps in boats, living on fish, shellfish, sea mammals, seabirds and seaweed. The archaeologist Jon Erlandson and colleagues called this rich coastal environment a kelp highway.

The main difficulty is evidence. Because sea levels rose after the Ice Age, the coastline people would have followed now lies under tens of metres of water, so most sites along it are lost or very hard to find.

The rise and fall of Clovis-first

In 1929 and the early 1930s distinctive stone spear points were found with mammoth bones at Blackwater Draw near Clovis, New Mexico. Similar fluted points, now called Clovis points, were found across North America. Radiocarbon dating later placed the Clovis culture at roughly 13,000 years ago, with recent estimates of about 13,050 to 12,750 years ago.

Because Clovis appeared to be the earliest widespread culture, and because it seemed to follow the opening of the ice-free corridor, many archaeologists came to believe that Clovis people were the first Americans. This Clovis-first model dominated thinking from the 1960s to the 1990s. Claims of older sites were usually rejected because of doubts about dating or about whether supposed tools were really made by humans.

The model began to crumble with Monte Verde in southern Chile, where Tom Dillehay excavated a settlement preserved under peat. It dated to about 14,500 years ago, more than a thousand years before Clovis, and lay near the southern end of the continent, more than 10,000 kilometres from Beringia. In 1997 a group of leading archaeologists visited the site and agreed that it was genuine. Most specialists date the end of the Clovis-first consensus to that visit.

Pre-Clovis sites

Since then a growing number of sites older than Clovis have been accepted. They include:

• Paisley Caves, Oregon: human coprolites (preserved faeces) with human DNA, dated to about 14,300 years ago.
• Page-Ladson, Florida: stone tools and a butchered mastodon tusk from a sinkhole, about 14,550 years old.
• Debra L. Friedkin site, Texas: thousands of stone artefacts in layers below Clovis, dated to about 15,500 years ago.
• Cooper’s Ferry, Idaho: artefacts and pits dated to about 16,000 years ago.
• Meadowcroft Rockshelter, Pennsylvania: a long-debated site with layers that its excavators date to about 16,000 years ago or earlier.

The most dramatic evidence comes from White Sands National Park in New Mexico. In 2021 a team led by Matthew Bennett reported human footprints, many apparently left by teenagers and children, in sediments dated by seeds of an aquatic plant to about 23,000 to 21,000 years ago. Critics argued the seeds might give misleadingly old dates. In 2023 a follow-up study using pollen and luminescence dating supported the original age. If correct, people were south of the ice sheets during the Last Glacial Maximum itself.

Some sites have been claimed to be much older still, such as Chiquihuite Cave in Mexico, with proposed dates of 26,000 years or more, and Pedra Furada in Brazil. These claims remain contested.

What ancient DNA reveals

Ancient genomes have transformed the field since 2014. The remains of a Clovis-era infant found at the Anzick site in Montana, known as Anzick-1 and dated to about 12,600 years ago, showed that Clovis people were directly ancestral to many living Native Americans, especially in Central and South America.

Genetic studies suggest that, south of the ice sheets, the founding population split around 15,000 years ago into two main branches, often called Northern and Southern Native Americans. The Southern branch spread rapidly through Central and South America. A separate group, the Ancient Beringians, known from an infant buried at Upward Sun River in Alaska about 11,500 years ago, remained in the north and left no known descendants.

The genome of Kennewick Man, a skeleton about 9,000 years old found in Washington State, showed in 2015 that he was closely related to living Native Americans, helping to resolve a long legal dispute over his remains. Some Amazonian groups also carry a faint genetic signal linked to Australasian populations, which researchers are still trying to explain.

Life in a new world

The first Americans entered landscapes no humans had ever seen, filled with animals such as mammoths, mastodons, giant ground sloths, horses and camels. Within a few thousand years many of these large animals had disappeared. Scientists still debate how far human hunting contributed, alongside rapid climate change at the end of the Ice Age, in the wider Quaternary megafauna extinction.

Early Americans were not only big-game hunters. Sites such as Monte Verde show people gathering wild plants, seaweed and shellfish, building shelters and using a wide range of resources. Their rapid spread from the Arctic to Patagonia, across deserts, rainforests and mountains, required great flexibility and detailed knowledge of very different environments.

Later arrivals

The first migration was not the last. Around 5,000 years ago the ancestors of the Palaeo-Inuit crossed from Siberia into Alaska and spread across the Arctic. About 1,000 years ago the Thule people, ancestors of today’s Inuit, expanded rapidly from Alaska to Greenland. Around the same time Norse voyagers briefly settled at L’Anse aux Meadows in Newfoundland, the first known Europeans in the Americas.

By the numbers

Timeline

• c. 26,000–19,000 years ago: Last Glacial Maximum; ice sheets block most routes south of Beringia.
• c. 23,000–21,000 years ago: People leave footprints at White Sands, New Mexico.
• c. 17,000–16,000 years ago: Parts of the Pacific coast become free of ice.
• c. 16,000 years ago: People are living at Cooper’s Ferry, Idaho.
• c. 14,500 years ago: A settlement flourishes at Monte Verde, Chile.
• c. 13,050–12,750 years ago: The Clovis culture spreads across North America.
• 1929–1930s: Clovis points are found at Blackwater Draw, New Mexico.
• 1997: Expert visit to Monte Verde ends the Clovis-first consensus.
• 2014: The Anzick-1 genome links Clovis people to living Native Americans.
• 2021: The White Sands footprints are dated to the Last Glacial Maximum.

Why it matters

The peopling of the Americas was one of the great migrations of human history, carrying people from the Arctic to the tip of South America in a few thousand years. Its story has changed dramatically in a generation, showing how new methods such as ancient DNA can overturn long-held views. It is also the deep history of the Indigenous peoples of the Americas, whose own traditions and rights are increasingly part of how that history is told.