What caused the extinctions of the wooly mammoth, giant sloth, mastodon, and other beasts? A new study makes a strong case that the answer is us. Scientists have long argued over the cause of the "Quaternary extinction"—which took out vast numbers of large mammals about 12,000 years ago—and while the new study won't end the debate, it's perhaps the most detailed look at it yet, analyzing 177 extinctions on a country-by-country basis, LiveScience reports. Researchers found the die-offs were much more tightly correlated with human arrival than with climate changes, which they viewed as the other most likely theory.
"The evidence really strongly suggests that people were the defining factor," the lead author says. Regions where humans arrived later, such as North America and Australia, saw the most extinctions—which makes sense because "you've got this very advanced hunter arriving in the system," he explains. Still climate did appear to play a role in some regions, and it's unclear if humans directly killed off all these species, or simply affected their habitats in a way that drove them to extinction, Science points out.
The study comes on the heels of another suggesting mammoths were done in by man's best friend, and research showing that neanderthals were probably much more formidable—and brainy—than we thought. (Read more woolly mammoth stories.)