In the News
DNA hints at
polar bears’
Irish ancestry
maternal line traced back to
brown bears on emerald isle
STORY ONE
Today’s polar bears may descend from a brown bear that lived in Ireland uring the Ice Age.
By Susan Milius
All polar o’bears living today may be able to trace their maternal ancestry back through grandmothers many
times great to a female brown bear
in Ireland.
Analyzing bits of maternally inherited DNA from 242 bear lineages, both
modern and fossil, suggests that polar
bears interbred with brown bears in
or near Ireland between 20,000 and
50,000 years ago, an international
team of scientists reports online July 7
in Current Biology. At the time, the
Emerald Isle had a much colder climate.
A major Irish brown bear ancestor “was
a complete shock,” says study coauthor
and geneticist Ceiridwen Edwards, now
at the University of Oxford in England.
While working at Trinity College in
Dublin, Edwards extracted fragments of
DNA from fossil brown bears found in
Irish caves. Her data were among those
combined to outline the last 120,000
years or so of maternal history for polar
and brown bears.
Biologists have known that even
today polar bears and brown bears are
related closely enough that they can
produce fertile hybrid offspring. Also,
genetic studies had hinted at ancient
connections of some sort between
polar bears and the brown bear popu-
lations of three islands off the coast
of Alaska. A lingering impact from
interbreeding around Ireland was an
unexpected twist in the tale.
Polar bears specialize in living on
Arctic ice, a habitat shrinking so fast
with climate change that the species
is now listed as threatened under the
Endangered Species Act. Polar bears
haven’t left much of a fossil record, but
genetic studies and other work have
suggested that the species arose from
coastal brown bears.
Polar bears and brown bears can still
be classified as distinct species even
if they can produce fertile offspring
now and then, notes coauthor and evolutionary geneticist Mark Thomas of
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July 30, 2011 | SCIENCE NEWS | 5
