A long-held theory about why great beasts like the woolly mammoth or saber-toothed tiger went extinct is the overkill hypothesis, which argues that early human predation took out the giant mammals roaming the Earth during the Late Pleistocene period. But new research suggests the mammals' demise isn't entirely on our distant ancestors' shoulders after all.
Research from a multinational team of scientists studying the vanishing of large mammals from South America indicates that an unfortunate collision between rapid climate warming and the expansion of humans drove the creatures out of existence.
The study, recently published in the journal Science Advances, used genetic data and carbon-dated bone samples to determine that a striking number of animals had died around the same time period, about 12,300 years ago. Humans had arrived around 3,000 years before the mass deaths and apparently lived for a time in a relatively balanced existence with the great animals.
It was only when a sudden and rapid warming period caused changes in plant growth and rainfall around the world that notable extinctions occurred. The research suggests these major climate shifts and hungry, predatory humans combined to spell the end.
While American Museum of Natural History mammal specialist Ross MacPhee told LiveScience that this new study was "a really substantial improvement in conceiving how these extinctions occurred," he saw some limits in the methods used to analyze the rate of climate change, such as a limited number of ice core samples. MacPhee said he didn't doubt the findings were valid, but was unsure that similar extinctions across the globe could be blamed on the same causes.
It's also worth noting that another mammal whose ancestors appeared to survive and thrive in South America, the guanaco, didn't really make it through either. Researchers found that modern guanaco DNA indicated it was only still around because a tiny group arrived after so many other animals had died—as a result, the herbivores had all the grass they could eat.