The long-ago extinctions of some of the world's largest animals were caused by both human activity and natural climate change, according to new research from the University of Cambridge.
The team examined extinctions during the late Quaternary period - from 700,000 years ago until the present day - but focused mainly on the last 100,000 years.
And they say they've been able to identify the main factors behind the demise of creatures such as mammoths, mastodons, giant sloths and woolly rhinos, along with giant kangaroos, wombats and moas.
The researchers used data from an Antarctic ice core, covering the last several hundred thousand years. They also compiled information on the arrival of modern humans from Africa in North America, South America, Eurasia, Australia and New Zealand.
And a statistical analysis of both types of data indicates that the animals' extinction was caused by a combination of climate change and the arrival of man - probably through hunting or habitat alteration.
"The loss of these animals has been a zoological puzzle since the time of Charles Darwin and Alfred Russel Wallace. At that time, many people didn't believe that human-caused extinctions were possible, but Wallace argued otherwise," says PhD student David Williams.
"We have now shown, 100 years later, that he was right, and that humans, combined with climate change have been affecting other species for tens of thousands of years and continue to do so. Hopefully, now though, we are in a position to do something about it."
The team says there are implications for large animals today.
"Our research suggests that a combination of human pressure and climate change was able to cause the extinctions of many large animals in the past. Many large, charismatic animals today are threatened by both hunting pressure and changes in climate," says PhD student Graham Prescott.
"If we do not take action to address these issues we may see further extinctions."