Drabeck figured that the receptor targeted by cobra neurotoxin had probably changed to prevent the neurotoxin from parking there. Once she had the blood from the zoos’ honey badgers, Drabeck extracted DNA and sequenced part of the gene that contains the blueprint for making the receptor. Drabeck discovered several mutations in that gene that tweak the receptor. Cobra neurotoxin fits as well in the tweaked receptor as an SUV in a compact’s parking spot—and therefore it can’t paralyze the honey badger’s breathing.
Drabeck wasn’t surprised by these mutations, but she was surprised when she compared the honey badger’s tweaks to those found in other mammals. These tweaks had evolved independently in at least four species: honey badgers, mongooses, hedgehogs, and pigs. The hedgehog—which loves to eat venomous snakes—wasn’t a surprise. But the pig? “We were pretty excited by that,” says Drabeck. She hadn’t expected pigs to have molecular defenses against venom; biologists knew wild pigs could survive snakebites but assumed that was because their thick skin and fat acts like armor against fangs. But wild pigs, like honey badgers, have long shared the same parts of the world as venomous snakes—giving them an incentive to evolve venom resistance. And that in turn has given the snakes an incentive to evolve more toxic venom.