Chillin' chipmunks.

No amount of snow could send ancient chipmunks packing. Scientists have found that most chipmunks living in Wisconsin and Illinois are related to ancestors that toughed out a cold spell.

Kevin Rowe and Ken Paige, biologists at the University of Illinois at Urbana-Champaign, used DNA (chemical that carries hereditary information) samples to trace the ancestors of 244 eastern chipmunks, Tamias striatus (tuh-MY-us stree-AT-us). Turns out, most are related to a population of hardy chipmunks that once lived next to a towering block of ice called the Laurentide ice sheet.

Throughout the last 2 million years, Earth's climate has bounced between periods of warmer and cooler temperatures, says Tom Hooyer, a geologist at the University of Wisconsin in Madison. During the last ice age (cold period when ice covered large areas of Earth), moving rivers of ice called glaciers spread outward from the Arctic. Result: About 18,000 years ago, a 1.6 kilometer (1 mile)-thick glacier blanketed much of northern North America. "You'd expect chipmunks to move southward to escape that harsh climate," says Paige. Instead, the fearless animals holed up in southwestern Wisconsin's Driftless Area, a region nearly surrounded by ice. "The Driftless Area probably had forest patches where the chipmunks could survive until the glaciers receded (melted back)," says Hooyer. How's that for a winter wonderland?