How did the people move across the land bridge from Asia to North America?

The Americas were the last (well, second-to-last if you count Antarctica) continents to be inhabited by early humans. Archaeologists estimate that people entered North America by crossing over the Bering Strait, which back then was a wide swath of land, about 15,000 years ago.      In other words, people got here by walking a very long distance.      Our image of this major migration is fanciful. When I teach about the peopling of the Americas, I show a slide of people purposefully trekking in a straight line on a tundra from Siberia to Alaska, as if there was some destination on the other side and the only way to get there was to follow the leader, one behind the other.      But the truth is that human migration is much more complex, as suggested by genetic evidence presented recently by Ugo Perego and Alessandro Achilli of the Università di Pavia, Italy. Using mitochondrial DNA, they found two rare haplotypes (gene groupings) in modern Native Americans that point to two simultaneous ancestral migrations into this part of the world. One group took the fast track down the Pacific Coast to Tierra del Fuego (they may have used boats for part of the journey) and the other came across the Strait, maybe even with the coastal folks,  and then took a sharp left turn past the ice sheet and spread out over inland North America.      But what compels people to walk that fast and that far into the unknown?      The most obvious reason is that one has to pack up and go because things are not so good at home. Long ago, that probably meant that the climate had changed and made life impossible. It might have become too hot or too cold or too wet, which in turn would have affected not only quality of life but also make survival a shaky proposition. Drought, flood, and temperature changes could certainly push people to move on.      Climate change also affects the food supply, and anthropologists have assumed that people came to the Americas because they were following food on the hoof. Humans are famous for wiping out big game as they go, so these early travelers might have been walking behind herds and not realizing they were covering new ground as they ate their way into the New World.      People also migrate when they are being chased. Back then, there weren't enough people to cause civil unrest, tribal warfare, or religious persecution, but there could have been conflicts over land use or hunting rights.      Or maybe, they came because they could. Humans seem to have a universal penchant for moving around, and not always under duress. These days, people sometimes move to have a new life in a new land, or just for fun. Sometimes they want a new view, an adventure, or they want to reinvent themselves.      Maybe the two major groups of people coming to the New World were looking for a new life and they found it beaching it to Tierra del Fuego or chasing the herds across the plains of Canada.

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Meredith F. Small is an anthropologist at Cornell University. She is also the author of "Our Babies, Ourselves; How Biology and Culture Shape the Way We Parent" (link (opens in new tab)) and "The Culture of Our Discontent; Beyond the Medical Model of Mental Illness" (link (opens in new tab)).

These people are called Paleoindians by archaeologists. The genetic evidence records mutations in mitochondrial DNA passed from mother to offspring that are present in today’s Native Americans but not in the Mal'ta remains. This indicates a population isolated from the Siberian mainland for thousands of years, who are the direct ancestors of nearly all of the Native American tribes in both North and South America – the original “first peoples”.

Around 14,000 BCE, people migrated from Siberia (Asia) to Alaska (North America) over  the Bering Land Bridge (map below).

Map of the Americas. The Bering Land Bridge between Asia and North America in 18,000 BCE is shown in dark green. The map also shows the extent of ancient civilizations in Central or Mesoamerica (Ellis and Esler, 2014).

How is this related to climate?

• During the last ice age, which peaked around 19,000 BCE and ended around 8,700 BCE, global sea levels were up to 100 meters lower than they are today because colder temperatures resulted in large amounts of water becoming frozen in glaciers.
• The Bering Land Bridge existed during this time of low sea levels. When the glaciers melted and sea levels rose to their present-day position, the land bridge flooded and formed the Bering Strait that now separates Asia from North America. See below for an interactive map of the Bering Land Bridge and the Bering Strait over time.

Map of the Bering Strait and the Bering Land Bridge over time (Cal years BP: “calibrated years before the present” or “calendar years before the present”) (from Wood, 2020).

Further Exploration

• New evidence found in Chiquihuite Cave, Mexico, including tools made from a type of limestone not originating from the cave itself, suggests that humans first arrived in North America possibly as far back as 28,000 BCE. At that time, the ice sheets covering North America during the last ice age were still extensive, which would have made cross-continental travel very difficult, and suggests that the Pacific coast was the more probable travel route. This idea is known as the Pacific Coastal Route Hypothesis.
  • This new research indicates that even though people likely reached North America no later than 24,500 to 17,000 BCE, occupation did not become widespread until the very end of the last ice age, around 12,700 to 10,900 BCE. 
  • This new evidence dispels the Clovis-first model, named for evidence of human occupation in Clovis, New Mexico. This model suggests that the first people to reach North America traveled across the Bering Land Bridge and then into North America along an ice-free cross-continental corridor around 14,000 to 8,000 BCE (map below). It is likely that  by then North America had already been occupied by people who migrated via the Pacific coastal route.
  • Under the Pacific Coastal Route Hypothesis, people traveled south along the “kelp highway” of the western coast of the Americas because it was mainly ice-free and therefore easier to traverse than the ice-covered inland areas (map below). The coastal waters had common giant kelp species such as Durvillaea antarctica and Macrocystis pyrifera, which supported rich ecosystems that provided food, such as sea bass, cod, rockfish, sea urchins, abalones, and mussels for the migrating people. At the end of the last ice age, glaciers melted and sea levels rose, flooding the “kelp highway.”

Map of North America during the Last Glacial Maximum, depicting both the coastal route suggested by the Pacific Coastal Route Hypothesis and the ice-free corridor route suggested by the Clovis-first model. Chiquihuite Cave is marked in red (from Gandy, 2020, National Geographic Magazine).

• After the initial migrations to North America, people began moving southward, following the Pacific coast from Alaska to Chile. Those who made it to northern and central South America were limited to small communities because the cold, harsh climate of the ice age prevented populations from expanding. A short period of rising temperatures and retreating glaciers followed, which allowed people to migrate further south and establish new settlements in Patagonia, such as in Monte Verde (map below). Then, around 12,500 BCE, in what is known as the Antarctic Climate Reversal, temperatures dropped as much as 6℃ below present-day and remained low for 2 millenia. When temperatures rose yet again, more glaciers melted, flooding the Strait of Magellan and cutting the southernmost settlements on Tierra del Fuego off from the mainland (map below), leading to a cultural division between mainland and coastal inhabitants.

Map of southern South America. The Patagonia region is shown in dark brown. Monte Verde, located on the western coast, is marked with a red dot. The Strait of Magellan, marked in blue, and Tierra del Fuego are at the southern tip of the continent (from Salbuchi, 2010).

References and additional resources:

• Ardelean, C. F., et al. “Evidence of human occupation in Mexico around the Last Glacial Maximum” Nature, vol. 584, no. 7819, 2020, pp. 87–92. DOI: 10.1038/s41586-020-2509-0. 
• Bacerra-Valdivia, L. and Higham, T. “The timing and effect of the earliest human arrivals in North America.” Nature, vol. 584, 2020, pp. 93-97. https://www.nature.com/articles/s41586-020-2491-6. 
• Daley, J. “First Humans Entered the Americas Along the Coast, Not Through the Ice.” Smithsonian. 2016. www.smithsonianmag.com/smart-news/humans-colonized-americas-along-coast-not-through-ice-180960103/. 
• Daley, J. “New Evidence Shows That Humans Could Have Migrated to the Americas Along the Coast.” Smithsonian. 2018. www.smithsonianmag.com/smart-news/new-evidence-shows-first-americans-could-have-migrated-along-coast-180969217/. 
• Dvorsky, G. “Humans Reached North America 10,000 Years Earlier Than We Thought, New Research Suggests.” Gizmodo. 2020. www.gizmodo.com/humans-reached-north-america-10-000-years-earlier-than-1844466373.
• Ellis, E. G. and Esler, A. High School World History (Pearson Student Edition, Survey Grade 9/12). Wilmington, Prentice Hall, 2014. 
• Gandy, D. “Surprise Cave Discoveries May Double the Time People Lived in the Americas.” National Geographic. 2020. www.nationalgeographic.com/history/2020/07/surprise-chiquihuite-cave-discovery-mexico-double-peopling-americas/?cmpid=org. 
• Geggel, L. “Humans Crossed the Bering Land Bridge to People the Americas. Here’s What It Looked Like 18,000 Years Ago.”

  How did people migrate from Asia to North America?

  The settlement of the Americas began when Paleolithic hunter-gatherers entered North America from the North Asian Mammoth steppe via the Beringia land bridge, which had formed between northeastern Siberia and western Alaska due to the lowering of sea level during the Last Glacial Maximum (26,000 to 19,000 years ago).

  Who migrated across the land bridge between Asia and North America?

  The first definitive archaeological evidence we have for the presence of people beyond Beringia and interior Alaska comes from this time, about 13,000 years ago. These people are called Paleoindians by archaeologists.

  What happened to the land bridge between Asia and North America?

  This exposed land stretched one thousand miles from north to south. As the ice age ended and the earth began to warm, glaciers melted and sea level rose. Beringia became submerged, but not all the way.

  How did humans and animals cross from Asia to North America?

  For more than half a century, the prevailing story of how the first humans came to the Americas went like this: Some 13,000 years ago, small bands of Stone Age hunters walked across a land bridge between eastern Siberia and western Alaska, eventually making their way down an ice-free inland corridor into the heart of ...