(Repeats for wider coding; story unchanged)
By Ben Hirschler
LONDON, April 19 (Reuters) – Polar bears evolved as a
separate species far earlier than previously thought, according
to a new genetic study, which adds to worries about their
ability to adapt in a rapidly warming world.
Research published on Thursday found the Arctic’s top
predators split off from brown bears, their closest relatives,
around 600,000 years ago – five times earlier than scientists
had generally assumed.
The finding suggests polar bears took a long time to adapt
to their icy world and may therefore struggle to adjust as the
Arctic gets warmer and the sea ice melts, depriving them of
vital hunting platforms.
Despite being a very different species in terms of body
size, skin and coat colour, fur type, tooth structure, and
behaviour, previous research had indicated that polar and brown
bears diverged only recently in evolutionary terms.
That assumption was based on studying mitochondrial lineage
– a small part of the genome, or DNA, that is passed exclusively
from mothers to offspring.
But after studying a lot more DNA from inside the cell
nucleus, using samples from 19 polar and 18 brown bears, Frank
Hailer of Germany’s Biodiversity and Climate Research Centre and
colleagues reached a very different conclusion.
They found both polar and brown bears were much older, as
species, according to a paper published in the journal Science
on Thursday.
“Previous studies suggested that polar bears would have had
to be evolving very rapidly, since they were so young,” Hailer
said in a telephone interview.
“Our study provides a lot more time for polar bears to adapt
… It makes more sense from an evolutionary standpoint that
polar bears would be older.”
His team’s calculations put the moment when the two types of
bears diverged in the Pleistocene period, when the climate
record shows that global temperatures reached a long-term low.
That could be coincidental but it suggests that the planet’s
cooling may have triggered the split.
While the latest research implies that past polar bear
adaptation was probably a slow process, it also means the
animals have been through warming phases before.
“If they go extinct in this phase of warming, we’re going to
have to ask ourselves what our role in that process was,” Hailer
said.
“In previous warm phases between the ice ages polar bears
were able to survive. The main difference this time is that
humans are impacting polar bears as well.”
Genetic studies are an important tool in researching the
evolutionary history of polar bears, since the animals typically
live and die on sea ice. As a result, their bodies sink to the
sea floor, where they get ground up by glaciers or remain
undiscovered, making fossils scarce.
(Editing by Maria Golovnina)
