Large mammals like mammoths, mastodons, and camels might still be roaming the Americas today if humans hadn't hunted them into extinction, a new study suggests.
Research from the University of Wyoming, published in journal Proceedings of the National Academy of Sciences on Monday, has added fuel to a longstanding hypothesis that humans played a major role in the mass extinction of large mammals between 13,300 and 15,000 years ago.
Looking at radiocarbon dates from fossils of the now-extinct mammals, researchers found decline of these species correlated with the migration of humans from across Alaska's Bering Strait, through North America, and into South America. The decline of the animals began 13,300-15,000 near the Bering Strait; between 12,900-13,200 years ago in the contiguous United States; and between 12,600-13,900 years ago in South America, the study found.
The findings support a hypothesis from 1973 by geoscientist Paul Martin that humans hunted the animals into extinction. Martin's theory contrasts with other extinction theories, including that the die-off was caused by disease humans brought with them, or by climate change.
"... (T)he north to south time-transgressive pattern is striking, and, barring significant new data, it would be difficult to reconcile this pattern with extinction hypotheses that invoke a single climatic, ecological or catastrophic extinction mechanism across the entirety of the Americas," the researchers wrote.
Todd Surovell, an archaeologist and author of the study, said the theories are not mutually exclusive, but that the new evidence makes a compelling argument for hunting as the main reason behind the extinction.
"This pattern is hard to reconcile with other extinction theories," he said. "For me, the evidence is pretty overwhelming that humans played a strong role in this event. If humans had never colonized the new world, it is very possible we'd still have mammoths today."
Some researchers have disputed that relatively small populations of humans could have caused such a large extinction event, but Surovell said simulations have shown our species can have a disproportionately large footprint.
"Assuming humans were not only hunting for subsistence, but taking more than they needed, an event of this scale would certainly be possible," he said. The study said there are several issues left to be resolved, including that the findings indicated the initial decline of mammals began earlier than estimated, suggesting humans may have entered the region earlier than is commonly thought, and that "more extensive investigations" are needed to resolve the issue.
In the study, researchers also wrote they would like "to reassert the value of using paleoecological data to study the human past." Surovell said creating a better understanding of past extinctions can help us understand present patterns, especially as we are now facing another man-made mass extinction event.
"Understanding what caused this extinction gives us insight into how to prevent them today
It's clear today, now that we have 7 billion people on the planet, that humans can have a massive impact on the environment. But what is important to realize is that even when you don't have that many people in an ecosystem, we can still have a huge impact on it," Surovell said.
"Compared to other animals we have a disproportionately heavy hand, and a huge impact."