Scientists have long debated why woolly mammoths, giant sloths and 44 more giant, plant-eating ‘megaherbivores’ went extinct starting around 50,000 years ago.
Some paleontologists, biologists and others have argued that drastic climate change events across the past two Ice Ages were responsible for the extinctions of these majestic creatures.
But a new study has landed on a different culprit: humans.
A sweeping review pooling together paleo-climate data, preserved DNA samples, archeological evidence and more has determined that ‘human predation’ from 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,’ researchers said, behind these species’ extinction.
Scientists have long debated why woolly mammoths, giant sloths and 44 more gigantic, plant-eating ‘megaherbivores’ went extinct starting around 50,000 years ago. Above, an engraving by Ernest Grise of prehistoric man hunting a woolly mammoth
Scientists refer to large animals — defined as anything greater than 99 pounds (45 kilograms) — as ‘megafauna.’ And their above-average rates of extinction in modern eras have caused both worry and fascination.
‘The large and very selective loss of megafauna over the last 50,000 years is unique over the past 66 million years,’ according to the study’s lead author Jens-Christian Svenning, who researches paleo-ecology 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 the megafauna extinctions.’
Svenning, who leads the Danish National Research Foundation’s Center for Ecological Dynamics in a Novel Biosphere (ECONOVO) at Aarhus University, managed a team of seven other researchers who helped compile the new study.
One intriguing set of artifacts and physical evidence from the archaeological record helped to 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 analyses of human bones and protein residues on recovered spear points all suggest that our ancestors capably hunted and ate some of the biggest mammals around.
‘Another significant pattern that argues against a role for climate is that the recent megafauna extinctions hit just as hard in climatically stable areas as in unstable areas,’ Svenning said.
But while a region’s vulnerability to climate change played no role in these extinctions, the incoming migration of human hunters did, Svenning’s team found.
The researchers noted that 40 of the 48 known large mammals during this period (top right of chart) went extinct, while only smaller and smaller percentages of the each lower ‘weight class’ of species died off. The bottom row breaks these extinction numbers down by continent
The fossil record shows that these large species went extinct at very different times and at widely differing speeds, some dropping off in number quite quickly and others more gradually — in some cases across 10,000 years or more.
Few of these extinctions are well matched by climate records from this time period, known as the late Quaternary period, which includes the tail end of the Pleistocene epoch, the past two Ice Ages, and the dawn of the Holocene epoch 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 the 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 survey of big animal extinctions from this time frame found that 40 of the 48 largest animals, those weighing over 2,200 pounds (1,000 kg), went extinct.
The percentages of extinctions tended to trend downward by weight class from there, suggesting that megafauna and the docile plant-eaters in particular had a big target on their backs.
In more recent millennia, from the past 5,000 years or so to present, the remaining megafauna have remained among those species most threatened by extinction from human activity, including poachers and habitat loss.
The researchers cited specifically the worldwide extinctions of the water buffalo species Bubalus mephistopheles, a horse or equid species called Equus ovodovi and the gibbon primate species Junzi imperialis.
They also raised alarm over the dwindling numbers of several megafauna in China, the elephant species Elephas maximus, two rhinoceros species Dicerorhinus sumatrensis and Rhinoceros sondaicus and Panthera tigris tigers.
The extinction of megafauna, according to Svenning, can undermine whole ecosystems, as the big creatures play a role in dispersing seeds, shaping vegetation by their eating habits, and contributing to the nutrient cycle via their waste.
‘Our results highlight the need for active conservation and restoration efforts,’ the researcher said.
‘By reintroducing large mammals, we can help restore ecological balances and support biodiversity,’ Svenning concluded, ‘which evolved in ecosystems rich in megafauna.’