A FEW MILES FROM THE ENDLESS MALLS and garish tourist attractions of Myrtle Beach, South Carolina, there's an exotic-animal preserve that houses a group of four-year-old liger brothers named Hercules, Zeus, Vulcan, and Sinbad. Ligers, the offspring of a lion father and tiger mother, are the world's largest cats, weighing up to half a ton each—double the heft of either parent. They're hybrids, and you won't see them in accredited American zoos, which look askance at letting different species breed. But that's how it is with hybrids: They don't get much respect and they're easy to miss, even when they're right under your nose.

And yet, when you start looking around, they're everywhere.

Zorses, wholphins, tigons, and beefaloes. Lepjags, zonkeys, camas, and bonanzees. These are some of the captive-bred mammalian hybrids that exist, and they're joined by a host of hybrid birds, fish, insects, and plants. Thanks to new techniques that allow scientists to isolate and compare DNA, more hybrids are turning up every year, and we're learning that some of them—such as the pizzly, a cross between a polar bear and a grizzly—can occur naturally in the wild.

Hybrids evoke wonder and fear, magic and folklore. Their very existence unsettles our concept of what's out there, now and in the past. In fact, scientists are currently debating the extent to which hybrid breeding may have occurred during the evolution of man. Some contend that interspecies hanky-panky between humans and chimps—resulting in, yes, "humanzees"—went on for a million years or more after the two species split off from a common ancestor. Even now, there may be ghostly traces of this forbidden genetic lambada in our chromosomes.

Sound hard to believe? That's the hybrid calling card. They strain credulity—even when they're staring you in the face.