by Mary Harrsch © 2025
We learned in Part I the migrants to the Americas about 12,000 years ago had roughly equivalent though varied technological tools as their counterparts in Eurasia. But, population density was low due to less than 5,000 migrants successfully completing their journey to the Americas during the period the Beringia Land Bridge was passable.
Images: Prehistoric megafauna of the Americas occupying the region that is now known as the John Day Fossil Beds in east-central Oregon. Photographs by Mary Harrsch of murals displayed at the John Day Fossil Beds Visitor Center.
The total land area of the Americas 12,000 years ago was approximately 42 million square kilometers. Eurasia at this same time is thought to have been populated by from 1 – 10 million people spread over 54 million square kilometers. DeepSeek suggests we use 5,000,000 as a median figure and calculate the density per 1,000 km2 at 93 people compared to the density of the Americas at 5,000/42,000,000 or only .12 people per 1,000 km2. This means that around 12,000 years ago, Eurasia’s population density was approximately 775 times higher than that of the Americas.
“Context and Implications
• Americas: The extremely low population density in the Americas reflects the fact that humans had only recently arrived and were still in the process of spreading across the continent. The vast, uninhabited landscapes would have limited interactions between groups, slowing the exchange of ideas and technologies.
• Eurasia: The higher population density in Eurasia was the result of tens of thousands of years of human habitation, during which populations grew and spread across the continent. The denser population would have facilitated trade, cultural exchange, and technological innovation.”
In the historical period, resource competition has been a factor prompting large scale migrations, so I asked DeepSeek “Had resource competition in Eurasia already reached a point to prompt human migration to the Americas 12,000 years ago?” DeepSeek didn’t seem to think it was the primary driver, though.
“The migration of humans to the Americas around 12,000 years ago (or possibly earlier, as suggested by some evidence) was likely driven by a combination of factors, including environmental changes, resource availability, and population dynamics. While resource competition in Eurasia may have played a role, it was not the sole or primary driver of this migration. Here’s a more nuanced look at the factors that likely contributed to the peopling of the Americas:
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1. Environmental Changes and the Opening of Migration Routes
• End of the Last Glacial Maximum: Around 16,000 to 14,000 years ago, the Last Glacial Maximum (LGM) ended, and global temperatures began to rise. This led to the retreat of ice sheets and the opening of migration routes into the Americas.
• Bering Land Bridge: During the LGM, lower sea levels exposed the Bering Land Bridge, connecting Siberia and Alaska. As the climate warmed, this land bridge became habitable, allowing humans and animals to cross.
• Ice-Free Corridor: Around 14,000 to 13,000 years ago, an ice-free corridor opened between the Cordilleran and Laurentide ice sheets in North America, providing a route for humans to move southward into the continent.
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2. Resource Availability and Exploration
• Abundant Resources in Beringia: Beringia, the region encompassing the land bridge and surrounding areas, was a rich ecosystem with abundant megafauna (e.g., mammoths, bison) and other resources. This likely attracted human groups to the region.
• Exploration and Expansion: Human populations have a long history of exploring and expanding into new territories, especially when resources are abundant. The movement into the Americas may have been part of this broader pattern of exploration and migration.
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3. Population Dynamics in Eurasia
• Population Pressure: While resource competition in Eurasia may have contributed to migration, it is unlikely to have been the primary driver. By 12,000 years ago, human populations in Eurasia were still relatively small and dispersed, and there were vast uninhabited or sparsely populated regions.
• Push and Pull Factors: Migration is often driven by a combination of "push" factors (e.g., resource scarcity, conflict) and "pull" factors (e.g., new opportunities, abundant resources). In the case of the Americas, the pull of unexplored, resource-rich lands was likely more significant than push factors in Eurasia.
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4. Cultural and Technological Factors
• Adaptability: Human groups that migrated into the Americas were highly adaptable, with the skills and technologies needed to survive in diverse environments. This adaptability allowed them to explore and settle new territories.
• Maritime Capabilities: Some evidence suggests that early migrations may have occurred along the Pacific coast, using boats. This would have required advanced maritime skills and technologies, further indicating that the migration was driven by exploration and resource-seeking rather than desperation.
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5. Timing of Migration
• Pre-Clovis and Clovis Cultures: Archaeological evidence, including pre-Clovis sites like Monte Verde in Chile (dated to around 14,500 years ago), suggests that humans may have entered the Americas earlier than 12,000 years ago. This timing aligns with the opening of migration routes and the availability of resources in Beringia and beyond.
• Multiple Waves: The peopling of the Americas likely occurred in multiple waves, with different groups entering at different times and by different routes (e.g., coastal and inland).
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6. Conclusion: Resource Competition as a Minor Factor
While resource competition in Eurasia may have played a role in prompting some groups to migrate, it was not the primary driver of the peopling of the Americas. Instead, the migration was likely driven by a combination of environmental changes (e.g., the opening of migration routes), the availability of abundant resources in Beringia and the Americas, and the innate human tendency to explore and expand into new territories. The timing and nature of the migration suggest that it was a gradual process, shaped by both ecological opportunities and human adaptability.
At this point, though, continuing climate change may have dealt the migrants in America a more challenging hand.
ChatGPT explains:
“The extinction of megafauna in prehistoric America occurred earlier and more rapidly than in Eurasia, likely due to a combination of climate change and human activity.
• Americas: Most megafauna, including mammoths, mastodons, giant ground sloths, and saber-toothed cats, disappeared between 13,000 and 10,000 BCE. This coincides with the arrival of the first widespread human populations (Clovis culture) and rapid climatic shifts at the end of the Pleistocene. The extinction event was particularly severe in North America, where around 70% of large mammal species vanished.
Megafaunal Diversity in the Americas
1. North America
o Mammoths (Columbian and woolly)
o Mastodons
o Giant ground sloths (e.g., Megatherium, Eremotherium)
o Short-faced bears (Arctodus)
o American lions (Panthera atrox)
o Saber-toothed cats (Smilodon)
o Giant beavers (Castoroides)
o Camelids (Camelops, extinct North American camels)
o Horses (extinct North American species)
o Glyptodonts (giant relatives of armadillos)
2. South America
o Giant ground sloths (even larger than North American species)
o Macrauchenia (a bizarre, long-necked herbivore)
o Toxodon (a large, hippo-like herbivore)
o Saber-toothed cats
o Terror birds (large, flightless carnivorous birds)
o Extinct horses and camelids
• Eurasia: Megafaunal extinctions were more gradual and regionally varied. Some species, like the woolly rhinoceros and European straight-tusked elephant, disappeared around 10,000 BCE, but others, such as bison and reindeer, survived in pockets much longer. The last woolly mammoths on Wrangel Island survived until about 2000 BCE.
Eurasian Megafauna (including Siberia and Europe)
o Woolly mammoths
o Woolly rhinos
o Cave bears
o Cave lions
o Steppe bison
o Giant deer (Megaloceros)
o Wild cattle (aurochs)
o Horses (which survived and were later domesticated)
But, the Americas saw a rapid, near-total collapse of megafauna in just a few thousand years, while Eurasian extinctions were spread out over a longer period.
So Why Did American Megafauna Seem to Disappear More Rapidly and Completely?
1. More Sudden Exposure to Human Hunters - In Eurasia, megafauna had coexisted with humans (Homo sapiens and earlier hominins like Neanderthals) for hundreds of thousands of years, possibly allowing species to evolve more wariness of human hunters. In contrast, the Americas were only recently populated by humans (~15,000–13,000 BCE. North and South American megafauna encountered efficient human hunters (e.g., Clovis culture) relatively suddenly, likely making them more susceptible to overhunting.
2. High Specialization of American Megafauna
Many extinct American megafauna were highly specialized to Ice Age conditions. For example:
1. Mammoths and mastodons thrived in open steppe environments, which shrank rapidly with warming.
2. Giant ground sloths relied on particular plant communities that were disrupted by climate change.
3. The short-faced bear, a hyper-carnivore, may have struggled as prey populations declined.
3. Lack of Geographic Escape Routes
In Eurasia, megafauna could migrate vast distances across connected landmasses, finding refuge in areas like Siberia and Wrangle Island. In contrast, American species had fewer options for migration, especially with the melting of the Laurentide and Cordilleran ice sheets creating barriers.
4. Rapid and Extreme Climate Shifts
At the end of the Pleistocene (c. 13,000–10,000 BCE), the Americas experienced abrupt climate shifts, including:
1. The Younger Dryas (c. 10,800–9,600 BCE): A sudden return to near-glacial conditions disrupted ecosystems, possibly reducing food availability.
2. Warming and Habitat Fragmentation: As ice sheets retreated, landscapes changed quickly, replacing megafauna-friendly open plains with forests and wetlands. This shift may have disrupted food chains before species could adapt.
5. Synergistic Effects of Climate & Hunting
While climate change alone likely stressed megafaunal populations, the simultaneous arrival of efficient human hunters (using advanced weapons and cooperative hunting strategies) created a "double whammy" that accelerated their decline. This is supported by evidence of human butchering marks on extinct species' bones, such as mammoths and giant sloths.
In short, American megafauna faced a perfect storm: a sudden climate shift, a lack of evolutionary experience with human hunters, and few options for migration or adaptation. These factors combined to make them highly vulnerable compared to their Eurasian relatives.
This rapid extinction in the Americas would lead to further dispersal of the small numbers of human hunting groups.
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