For decades now, scientists have debated why prehistoric behemoths such as the wooly mammoth, the wooly rhino, the saber-toothed tiger and the giant armadillo all went extinct between 80,000 and 10,000 years ago. Climate change, species-wide disease outbreaks and even a massive asteroid impact have been put forward as possible causes of their disappearance, but new evidence places the majority of the blame on a single source: mankind.
As part of a study recently published in the journal Ecography, scholars from the universities of Exeter and Cambridge conducted an exhaustive statistical analysis that cross-referenced ancient climate and human migration data with the suspected extinction dates for different species of “megafauna”—the collective name for the massive mammals that once roamed the planet. The results showed that while climate spikes certainly played a part in the disappearance of creatures like the wooly mammoth, they weren’t completely wiped out until humans invaded their turf.
“As far as we are concerned, this research is the nail in the coffin of this 50-year debate—humans were the dominant cause of the extinction of megafauna,” lead author Lewis J. Bartlett said in a University of Exeter press release. “What we don’t know is what it was about these early settlers that caused this demise. Were they killing them for food, was it early use of fire or were they driven out of their habitats? Our analysis doesn’t differentiate, but we can say that it was caused by human activity more than by climate change. It debunks the myth of early humans living in harmony with nature.”
Researchers have long struggled to explain the peculiar circumstances of the megafauna die-off that took place during the late-Pleistocene and early Holocene epochs—an event known as the Quaternary extinction. While many of the planet’s large terrestrial creatures vanished in the span of just 70,000 years—a blink of an eye in geological terms—the disappearances occurred at different periods on each continent. Even stranger, similar mass extinctions didn’t take place among smaller animals or marine life.
In recent years, debate over what caused the mysterious cull has largely centered on human intervention and climate change. Proponents of the climate theory argue that rapid temperature spikes drove the animals to extinction by transforming their habitat and reducing their food supply. Other scientists point the finger at Ice Age-era humans, who may have outcompeted the animals for resources or killed them off by hunting—an idea known as the “overkill hypothesis.” It’s widely accepted that early human colonists drove the massive moa birds of New Zealand into extinction, and anthropologists have discovered the remains of more than a dozen North American mastodons and mammoths that appear to have been killed by prehistoric hunter-gatherers.
The researchers in the new study used fossil records, literature reviews and high-resolution climate reconstructions to get a clearer picture of how climate and human colonization may have figured in megafaunal extinction. To account for discrepancies in the dating, the team used computer modeling to repeat the analysis over a range of 1,000 different “extinction scenarios.” The findings showed that extinctions followed a pattern that closely matched human migration across the globe, which suggests that mankind may have had a central role in the creatures’ demise. Climate change also played a part, but according to the researchers, its impact was less pronounced and unfolded over a significantly longer time period.
The models also indicate that human impact on extinction rates varied from place to place. In small and isolated habitats like islands, megafaunal die-offs tended to peak at around 8,000 years after humans arrived. On continents, the process took much longer, anywhere from 10,000 to 12,000 years. The researchers say their simulations proved least reliable for continental Asia, where neither human nor climate factors appear to have caused large-scale extinctions. “Whilst our models explain very well the timing and extent of extinctions for most of the world, mainland Asia remains a mystery,” said Cambridge University’s Dr. Andrea Manica. “According to the fossil record, that region suffered very low rates of extinctions. Understanding why megafauna in mainland Asia is so resilient is the next big question.”
The new study is only the latest chapter in the ongoing debate over megafaunal mass extinction. Just last month, researchers from the universities of Adelaide and New South Wales in Australia published a paper in the journal Science that found completely different results about the role humans and climate change played in the die-offs.
That study compared ancient DNA and radiocarbon data against geologic records of late-Pleistocene climate and concluded that rapidly warming temperatures—not humans—were the driving force in wiping out the wooly mammoth and its supersized brethren.