Tuesday, July 24, 2012
Polar bears may have trod the planet for millions of years, according to a new genetic analysis. That suggests the white-coated, massive bears have weathered previous natural climate changes, and may predate the Arctic ice that is their preferred—and only—habitat today, which is why the species future remains uncertain presently. "There's no guarantee that they'll survive this time," says geneticist Webb Miller of Pennsylvania State University, an author of the study published July 23 in Proceedings of the National Academy of Sciences. After all, Miller notes, the species currently lacks much genetic diversity to help it adapt to changing conditions as well as facing unprecedented threats such as heavy metal pollution accumulating in the Arctic. By better understanding how old the species is, the scientists hope to better understand what might be done to allow the polar bear to cope with onrushing climate change and other existential challenges. By analyzing the genomes of 28 bears—polar bears, including a roughly 120,000-year-old specimen from Norway's Svalbard archipelago, as well as modern brown bears and black bears—the scientists in effect read back in time to a common ancestor at least four million years ago. That finding conflicts with a genetic analysis published in Science earlier this year that suggested the species was only 600,000 years old or so, which the team behind the new research suggests may result from misreading past interbreeding events with closely related brown bears. In fact, the key problem here may be that technically the polar bear may not be a species at all. "If one defines that two species separate as when they cannot produce viable offspring, then perhaps brown bears and polar bears aren't yet separate species," Miller admits.