Scientists have long debated why woolly mammoths, giant sloths and 44 other giant, plant-eating “megaherbivores” went extinct about 50,000 years ago.
Some paleontologists, biologists, and others argue that drastic climate changes during the last two ice ages are responsible for the extinction of these majestic creatures. But a new study zeroed in on a different culprit: humans.
An in-depth review pulling together 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 pressure from behaviorally modern humans,” the team concluded in their new study.
Humans were the “key driver,” the researchers said, behind the extinction of these species.
Scientists have long debated why woolly mammoths, giant sloths and 44 other giant, plant-eating “megaherbivores” went extinct about 50,000 years ago. Above, engraving by Ernest Gries of a prehistoric man hunting a woolly mammoth
Scientists refer to large animals — defined as anything over 99 pounds (45 kilograms) — as “megafauna.” And their above-average extinction rates in modern eras have caused both concern and fascination.
“The large and highly selective loss of megafauna over the last 50,000 years is unique to the last 66 million years,” according to study lead author Jens-Christian Svenning, who studies paleoecology and biodiversity at Aarhus University.
“Previous periods of climate change have not resulted in large, selective extinctions,” Svenning noted in a statement, “contradicting a major role of climate in the extinction of megafauna.”
Svenning, who directs the Danish National Research Foundation’s Center for Ecological Dynamics in a New Biosphere (ECONOVO) at Aarhus University, led a team of seven other researchers who helped put together the new study.
An intriguing array of artifacts and physical evidence from the archaeological record helped bolster 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 exposed spearheads, suggest that our ancestors skillfully hunted and ate some of the largest mammals around.
“Another important pattern that argues against a role for climate is that recent megafauna extinctions affect both climatically stable and unstable areas equally,” Svenning said.
But while a region’s vulnerability to climate change did not play a role in these extinctions, the in-migration of human hunters did, Svenning’s team found.
The researchers note that 40 of the 48 known large mammals during this period (top right of the chart) went extinct, while only smaller and smaller percentages of each lower “weight class” species died out. The bottom row breaks down these extinction numbers by continent
The fossil record shows that these large species went extinct at very different times and at very different rates, some declining quite rapidly and others more gradually, in some cases over 10,000 years or more.
Few of these extinctions correlate well with the climate record of 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 have been linked to the local arrival of modern humans.
“Early modern humans were efficient hunters of even the largest animal species and apparently had the ability to reduce populations of large animals,” Svenning noted.
“These large animals were and are particularly vulnerable to overexploitation because they have long gestation periods, produce very few offspring at a time and take many years to reach sexual maturity,” he added.
His team’s study of large animal extinctions from that time period found that 40 of the 48 largest animals, those weighing more than 2,200 pounds (1,000 kg), were gone.
From here on out, extinction rates tend to decrease by weight class, suggesting that megafauna, and docile herbivores in particular, have a big target on their backs.
In recent millennia, from the last 5,000 years or so to the present, the remaining megafauna have remained among those species most at risk of extinction from human activities, including poaching and habitat loss.
The researchers specifically cited the worldwide extinction of the water buffalo species Bubalus mephistophelesa kind of horse or equid, called Equus ovodovi and the gibbon primate species Junzi Imperial.
They also raised alarm over the declining 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, according to Svenning, could undermine entire ecosystems because the large creatures play a role in seed dispersal, shaping vegetation through their feeding habits and contributing 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,” concluded Svenning, “that developed in ecosystems rich in megafauna.”
