Scientists have long debated why mammoths, giant sloths and 44 other giant plant-eating “megaherbivores” became extinct about 50,000 years ago.
Some paleontologists, biologists, and others have argued that drastic climate changes during the last two ice ages were responsible for the extinction of these majestic creatures. But a new study landed on another culprit: humans.
An extensive review compiled of paleoclimate data, preserved DNA samples, archaeological evidence, and more found that “human predation” by early hunter-gatherers is now the explanation most supported by all available evidence.
“There is strong, cumulative support for direct and indirect pressures from behaviorally modern humans,” the team concluded in their new study.
Humans were the “key driver”, scientists said, behind the extinction of these species.
Scientists have long debated why mammoths, giant sloths and 44 other gigantic plant-eating “megaherbivores” became extinct about 50,000 years ago. Above, an engraving by Ernest Gris of a prehistoric man hunting a woolly mammoth
Scientists refer to large animals — defined as anything larger than 99 pounds (45 kilograms) — as “megafauna.” And their above-average extinction rate in modern times has caused both concern and fascination.
“The large and highly selective decline of megafauna in the last 50,000 years is unique in the last 66 million years,” says lead study author Jens-Christian Svenning, who researches paleoecology and biodiversity at Aarhus University.
“Previous periods of climate change did not lead to large, selective extinctions,” Svenning noted in a statement, “which argues against a major role for climate in megafauna extinctions.”
Svenning, who heads the Danish National Research Foundation’s Center for Ecological Dynamics in the New Biosphere (ECONOVO) at Aarhus University, led a team of seven other researchers who helped put together the new study.
One interesting set of artifacts and physical evidence from the archaeological record helped support their conclusions, published this March in the journal Cambridge Prisms: Extinction.
Ancient traps designed by prehistoric humans to catch very large animals, as well as analyzes of human bones and protein residue on recovered spearheads, all indicate that our ancestors were able to hunt and eat some of the largest mammals around.
“Another significant pattern that argues against a role for climate is that recent megafauna extinctions have hit climate-stable areas as hard as unstable areas,” Svenning said.
But while the region’s vulnerability to climate change played no role in these die-offs, the inbound migration of human hunters did, Svenning’s team found.
The researchers noted that 40 of the 48 known large mammals became extinct during this period (top right of the graph), while only a smaller and smaller percentage of each lower “mass class” of species became extinct. In the bottom row, these extinction numbers are broken down by continent
The fossil record shows that these large species became extinct at very different times and at very different rates, with some declining in numbers relatively quickly and others gradually—in some cases over 10,000 years or more.
Few of these extinctions correspond well with the climate record from this time period, known as the Late Quaternary, which includes the end of the Pleistocene epoch, the last two ice ages, and the dawn of the Holocene epoch 11,700 years ago.
But many of these extinctions were associated with the local arrival of modern humans.
“Early modern humans were efficient hunters of even the largest animal species and clearly had the ability to reduce populations of large animals,” Svenning noted.
“These large animals were and are particularly vulnerable to overexploitation because they have a long gestation period, produce very few offspring at a time and take many years to reach sexual maturity,” he added.
His team’s survey of large animal extinctions from that time frame found that 40 of the 48 largest animals, those weighing more than 2,200 pounds (1,000 kg), went extinct.
From there, the extinction percentage tended to decrease by mass category, suggesting that the megafauna, and especially the docile herbivores, had a big target on their backs.
In recent millennia, from the last roughly 5,000 years to the present, the remaining megafauna have remained among the species most at risk of extinction due to human activities, including poaching and habitat loss.
The researchers specifically cited the worldwide extinction of water buffalo species Bubalus mephistophelesa horse or horse-like species called Equus ovodu and the gibbon species of primate Junzi imperialis.
They have also raised alarm over the dwindling numbers of several megafauna in China, the elephant species Elephas maximustwo species of rhinoceros Dicerorhinus sumatrensis and Rhinoceros sondaicus and Panthera tigris tigers.
The extinction of megafauna can undermine entire ecosystems, according to Svenning, because the large creatures play a role in seed dispersal, shape vegetation through their eating habits, and contribute to nutrient cycling through their waste.
“Our results highlight the need for active conservation and restoration efforts,” the researcher said.
“By reintroducing large mammals, we can help restore the ecological balance and support the biodiversity,” Svenning concluded, “that evolved in megafauna-rich ecosystems.”