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 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 has uncovered a different culprit: humans.
A comprehensive review that brought together paleoclimate data, preserved DNA samples, archaeological evidence and more has determined 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 factor” behind the extinction of these species, the researchers said.
Scientists have long debated why woolly mammoths, giant ground sloths and 44 other gigantic plant-eating “megaherbivores” became extinct about 50,000 years ago. Above, an engraving by Ernest Grise of prehistoric man hunting a woolly mammoth
Scientists call large animals (anything weighing more than 100 pounds) “megafauna,” and their higher-than-average extinction rates in modern times have caused both concern and fascination.
“The large and highly selective loss of megafauna over the past 50,000 years is unique in the past 66 million years,” said the study’s lead author. Jens Christian Svenningwho researches paleoecology and biodiversity at Aarhus University.
“Previous periods of climate change did not lead to large selective extinctions,” Svenning said in a statement, “which argues against a major role for climate in megafaunal extinctions.”
Svenning, who heads the National Research Foundation of Denmark’s Centre for Ecological Dynamics in a New Biosphere (ECONOVO) at Aarhus University, led a team of seven other researchers who helped compile the new study.
An intriguing set of artifacts and physical evidence from the archaeological record helped bolster their conclusions, published in March in the journal Cambridge Prisms: Extinction.
Ancient traps, designed by prehistoric humans to catch very large animals, as well as analyses of human bones and protein residues on recovered spearheads, suggest that our ancestors skillfully hunted and ate some of the largest mammals around.
“Another significant pattern that contradicts a role for climate is that recent megafaunal extinctions affected climatically stable areas just as strongly as unstable ones,” Svenning said.
But while a region’s vulnerability to climate change played no role in these extinctions, incoming migration of human hunters did, Svenning’s team found.
The researchers observed that 40 of the 48 large mammals known during this period (top right of the graph) became extinct, while only a decreasing percentage of each lower “weight class” of species died out. The bottom row breaks down these extinction figures by continent.
The fossil record shows that these large species became extinct at very different times and at very different rates: some disappeared in numbers quite rapidly and others more gradually (in some cases over 10,000 years or more).
Few of these extinctions match the climate record for this period, known as the Late Quaternary, which includes the end of the Pleistocene, the last two Ice Ages and the beginning of the Holocene 11,700 years ago.
But many of these extinctions were linked to the local arrival of modern humans.
“Early modern humans were effective hunters of even the largest animal species and clearly had the ability to reduce populations of large animals,” Svenning said.
“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 major animal extinctions during this time period found that 40 of the 48 largest animals — those weighing more than 2,200 pounds (1,000 kg) — went extinct.
Extinction rates tended to decline by weight class from there, suggesting that megafauna and docile herbivores in particular had a big target on their backs.
In more recent millennia, from the last 5,000 years or so to the present, the remaining megafauna have remained among the species most threatened with extinction by human activity, including poachers and habitat loss.
The researchers specifically cited global extinctions of the water buffalo species. Bubalus Mephistophelesa kind of horse or equine called Equus ovodovi and the gibbon primate species Imperial Junzi.
They also warned about the decline in the number of several megafauna in China, the elephant species Maximum elephanttwo species of rhinoceros Dicerorhinus sumatrensis and Rhinoceros sondaicus and Panthera tigris tigers.
The extinction of megafauna, according to Svenning, can undermine entire ecosystems, as the large creatures play a role in dispersing seeds, 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,” said the researcher.
“By reintroducing large mammals, we can help restore ecological balance and support biodiversity,” Svenning concluded, “which evolved in megafauna-rich ecosystems.”