Hunting -- Not Ice Age -- Changed European Bear DNA
Many brown bears likely roamed throughout the chilly expanses of southern and central Europe during the last Ice Age, 20,000 years ago, a new DNA analysis has found.
The research challenges the theory that the bears retreated south at the onset of the Ice Age, experts say.
It also suggests that hunting may have had more to do with the fragmented genetics of modern bears—such as this animal in Sweden—than ancient climate change.
Photograph by Iconica/Getty Images
Brian Handwerk
for National Geographic News
December 3, 2007
Humans may have influenced modern bear genetics far more than climate change in the last Ice Age, challenging a long-held theory, a new study says.
Scientists have long thought that the only European brown bears that survived central Europe's Ice Age 20,000 years ago lived in warm-weather southern refuges, such as modern-day Italy and Spain.
When temperatures rose again, and ice that once stretched as far south as Germany retreated, bears gradually spread into central and northern Europe, the theory holds.
The animals then became isolated in Spain, Italy, the Balkans, and Scandinavia, but their previous isolation had left a distinct genetic pattern. (See a map of Europe.)
Surprising mitochondrial DNA samples acquired from 20,000-year-old bear fossils may have turned this idea on its head.
The samples suggest large populations of bears likely roamed throughout the chilly expanses of southern and central Europe during even the worst periods of the Ice Age, according to study lead author Anders Götherström of Sweden's Uppsala University.
Not Your Average Bear?
The ancient bear DNA revealed the mixing of animals between far-flung locales, even when the ice cover was at its maximum.
(Related news: "Ancient Bear DNA Mapped -- A 1st for Extinct Species" [June 6, 2005].)
"The way we interpret it is that we [had] bears free to move around central Europe during the Ice Age," said Götherström.
The predators did not have to go south to survive, he added.
"The [existing] highly fragmented populations are what remain [after] the bear has become extinct from much of its major distribution in Europe," he said.
"From this very limited data set we've been trying to draw conclusions on what went on in central Europe without even having bears in central Europe.
"When we get access to [ancient DNA samples] from a wider part of the historic distribution of brown bears, it's not surprising that we get different conclusions."
Götherström also reports that some central European bear fossils have recently been dated to the time of the height of the Ice Age#8212;adding evidence to the new theory.
The research appeared in the latest issue of Molecular Ecology.
Hunting Pressures
With Mother Nature off the hook, human hands may have played a greater role in shaping modern bear genetics, the authors suggest.
As Europe's wilderness areas were gradually settled, bears were hunted and eventually fragmented into the isolated populations that survive today.
Lisette Waits of the University of Idaho's Conservation and Ecological Genetics Lab, who was not involved in the study, called its results both "convincing and intriguing."
"The authors suggest that the current structure might be explained simply by genetic drift that occurred when populations were reduced in size and became isolated due to human pressures of habitat loss and hunting," she said.
Boosting Bear Populations
The findings could have conservation implications for today's populations of European brown bears—many of which are fighting for a foothold in a highly populated continent.
Waits noted that some previous mtDNA analyses had been used to argue against efforts to supplement small bear populations with animals from other groups, because doing so might mix distinct genetic groups.
But "this work suggests that the isolation is more recent [and] does not trace back to the [last Ice Age], so these results could open the door" for such policies.
Study co-author Cristina E. Valdiosera is from Madrid's Centro Mixto UCM-ISCIII de Evoluciòn and Comportamiento Humanos.
"A big debate in conservation genetics [concerns] if you can translocate bears from one population to another," she said.
"We need to do other studies, but if we had bear populations connected until recent times, there should not be a reason why we could not translocate bears into the populations in Italy or Spain that are in danger of extinction."
