Sharon Jansa finds that some opossums survive snake bites by staying a step ahead of evolutionary "upgrades" in the potency of viper venom.

Whoever heard of a mild-mannered marsupial like the Virginia opossum eating rattlesnakes? Rattlesnakes strike with lightning speed; yet certain opossums not only survive, but go on to eat the snakes. How do they do it?

In a new study, University of Minnesota researcher Sharon Jansa and colleague Robert Voss of the American Museum of Natural History show that rapid evolution of a blood protein keeps the Virginia opossum and related species one step ahead of evolutionary "upgrades" in the potency of the viper's venom.