For a long time, it's been thought that polar bears are recent descendants of brown bears and that their white coats and webbed feet evolved into being over the last 150,000 years. A new study proves that incorrect: in fact, polar and brown bears share a common ancestor, making polar bears 600,000 years old.
The study, published in the this week's issue of Science, analysed DNA samples taken from polar, brown and black bears to try and understand their origins.
Previous estimates of the polar bear's lineage have studied mitochondrial DNA—but that gives an incomplete picture of evolution as it's only passed through females. Instead, this new study looked at 14 stretches of nuclear DNA—which comes from both parents—which in turn provides a more accurate result.
The team responsible for the work, who are based at the Biodiversity and Climate Research Center in Frankfurt, Germany, found that polar bears "are older and much more genetically unique" than previously thought. In fact, brown and polar bears represent completely separate lineages.
While it might seem odd that we know so little about the evolutionary history of such an iconic animal, that's down to the fact that they live mostly on sea ice. As a result, there are next to no polar bear fossils preserved on land—which has made tracing their history difficult. [Science and New York Times]
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