Polar bears eat copious amounts of fat. Their diet consists mostly of plump seals, and fat accounts for as much as 50 percent of a bear's body weight. So why don't polar bears develop heart disease, the way humans who consume too much fat sometimes do? The answer lies in the great white bear's unusual genes. In studying polar bear and brown bear genomes, Rasmus Nielsen of the University of California-Berkeley and colleagues discovered that polar bears diverged from brown bears about 400,000 years ago. As they adapted to surviving in an increasingly cold and harsh Arctic environment, genes associated with the cardiovascular system mutated in ways that allowed polar bears to eat massive amounts of lipids without developing heart disease.
Evolution in Action
Pinpointing when polar bears broke away from brown bears and blazed their own evolutionary path is key to understanding what drove the gene mutations and how fast large mammals like bears can adapt to extreme environments, the researchers note in the paper. Polar bears most likely evolved from brown bears after becoming isolated from other populations by a cooling climate. What's more, they adapted especially quickly in evolutionary time: about 20,500 generations. The analysis, combined with recent fossil data, "provides us with an unprecedented timeframe for rapid evolution," the researchers write in the paper
, published in today's edition of the journal Cell. "Here you have two species that fundamentally differ in ecology, diet, and behavior, and they diverge in a relatively short amount of time," Nielsen says.
Emulating Polar Bears
So could humans eventually develop similar genetic workarounds, allowing us to eat lots of french fries and cheeseburgers without risking an early death from heart disease? It's possible, but those adaptations would likely take hundreds of thousands of years, Nielsen says. "It's probably not worth waiting for," he jokes. Still, the polar bear study and other genome analyses can tell us something important about the future of our own species, he says: "If you want to learn something about [human] health, looking at some of these organisms that have gone through these changes already is a useful tool."
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