Climate drove the woolly rhino to extinction but early humans are more likely to blame for the demise of the bison, the wild horse and perhaps the mammoth too, according to a study released Wednesday.

"Some of both," in other words, is the answer to a long-standing wrangle as to whether climate shift or hunter-gatherers drove most of the northern hemisphere's Ice Age megafauna to an early grave, the study says.

For decades, experts have argued about the fate of these chill-loving mammals, which roamed the wilderness -- their numbers falling and rising with each glacial cycle -- for nearly two million years.

And then, after the peak of the last Ice Age about 20,000 years ago, things started to go wrong.

"The question is, what changed?" asked Beth Shapiro, a researcher at Penn State University and a co-author of the study.

"Why were these mammals no longer able to find safe 'refugia', or havens, where they could survive in a warm climate?"

Several dozen investigators led by Eske Willerslev of the University of Copenhagen sifted through genetic, climatic and archaeological data for six species: the woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox.

Genetic data made it possible to estimate roughly when and by how much populations of each species expanded or shrank as the climate changed and their habitat started to disappear.

This, in turn, was matched against shifts in temperature and precipitation as temperatures cooled and warmed across various glacial eras.

Finally, the archaeological clues showed the extent to which early humans might have influenced their survival.

"In locations where animal bones had been cooked or converted into spears, we know that humans lived there and were using them as a resource," Shapiro said.

Even without hunting, the overlap of human communities and animal ranges could have influenced whether the mammals survived, she added.

The picture that emerged is different for each species.

Homo sapiens never shared a living space with either the woolly rhino in Europe or the musk ox across Eurasia, the study showed.

This exculpates humans from their extinction in these locations and points to climate change as the likely cause.

For the other four big mammals, though, humans almost certainly helped shape their fate, but not always negatively.

"Something kept these animals from doing what they had always done before, which is finding an alternative refugia," said Shapiro. "That 'something' was probably us -- humans."

The combined evidence points an accusing finger at our species for the demise of the wild horse and the bison, especially across Siberia and in Asia.

Reindeers managed to find safe habitat in high arctic regions, escaping both rising global temperatures and humanity's voraciousness.

Why the woolly mammoth disappeared is still hotly debated, but the causes are probably multiple, the study concluded.

The last known population of the lumbering behemoths lived in isolation until 4,000 years ago on Wrangel Island, north of Siberia in the Arctic Ocean.