Humans aren’t to blame for wiping out most of the large mammal species at the end of the last ice age – at least not completely.
A new study, which will be published Wednesday in the scientific journal Nature, found there is no single explanation for the mass extinction of so many large mammals.
Both human activity and climate change probably played a role in the extinction event, but the demise of each species was caused by a combination of factors unique to them.
“We found it isn’t a simple story,” said Duane Froese, an associate professor at the University of Alberta who coauthored the study.
“There isn’t just a single cause that you can point to to understand what happened to these populations.”
At the end of the last ice age, more than 70 per cent of North America’s large mammal species went extinct. Eurasia lost 36 per cent of its large mammals. The arrival of humans in North America, around 12,000 years ago, coincided with the mass extinction of most of the continent’s megafauna.
That led to speculation humans were to blame for their disappearance.
For Froese, that explanation never seemed plausible.
“Imagining that early people, who were probably in fairly small numbers, hunted all of these animals to extinction seems a little bit unlikely,” he said.
This study, one of the most expansive of its kind, lays a lot of that speculation to rest.
More than 40 academic institutions took part in the study. Eske Willerslev, of the University of Copenhagen in Denmark, led the research team.
The study looked at the six ice age species: woolly mammoth, woolly rhinoceros, bison, reindeer, horse and musk ox.
Over four years, the research team examined a multitude of fossils, from which they extracted thousands of DNA samples.
By looking at the genetic variations among the different species for the first time, researchers estimated the size of each population throughout the ice age.
“What we saw was that the populations, for the most part, tracked changes in climate over time,” said Froese.
“To see how these populations changed before the extinction event is something we’ve never been able to do before,” said Grant Zazula, a Yukon government paleontologist who worked on the study.
Many of the fossils the research team used came from the Klondike.
During the last ice age, glaciers covered most of North America.
While Whitehorse was covered by a sheet of ice, Dawson City was free and clear, making it a prime region for ice age fossils.
Because the bones, soft tissue and hair are usually found in permafrost, the DNA often remains intact, allowing scientists to study not only the appearance of long-dead animals, but their genetics as well.
“Though (genetic analysis) is still relatively expensive, in the last decade it’s gotten much cheaper to do,” said Zazula. “It’s allowing us to look at things from a biological perspective.”
And that’s allowing scientists a much clearer picture of how these animals disappeared.
The ice age wasn’t always cold. The climate warmed and cooled several times over 50,000 years.
The study found the populations of large mammals waxed tand waned with those climatic changes.
When it got warmer, populations shrank, only to rebound when it got cold again.
“Most of these large mammals had been around for a few hundred thousand years and they had gone through previous times where climate warmed abruptly and they survived,” said Froese. “Something very different happened for at least some of these species during the last warming phase about 10,000 years ago.”
It was during that last warming period that humans showed up.
“It might be the case that humans showed up at the absolute worst time,” said Froese. “Climate may have taken these populations to the edge and humans showed up at the wrong time and pushed them over.”
While there is a lot of evidence Stone Age people hunted many of these large species, they didn’t necessarily hunt them to death, said Froese.
“It may be that they indirectly affected these populations by cutting off their ability to migrate to other areas, or they may have been occupying areas of prime habitat for these animals,” he said. “There are a number of ways that they might have interrupted the life cycle of these species.”
People tend to think of the mass extinction of ice age mammals as one big event caused by people, said Zazula.
But that’s not what this study has found, he said. The picture is much more complex
“It wasn’t so much a catastrophic event as a lot of things happening,” said Zazula.
He hopes this study will help raise the profile of paleontology and archeology in the Yukon.
Many of the fossils discovered in the territory aren’t found by scientists, but by placer miners.
“In the last couple of years we’ve really been building that relationship with miners,” said Zazula. “We’re trying to dispel the myth that if they discover something, we’re going to shut their operation down.”
An important study like this should help people realize the importance of collecting fossils, said Zazula.
“People are actually doing things with them,” he said. “People from all over the world come to study them.”
The Klondike is one of the most important areas in the world for this kind of work, said Zazula.
“There’s been invasive species coming over from Asia for millennia,” he said. “It’s a real crossroads.”
Contact Josh Kerr at