Human Papillomavirus (excerpt)
by Carl Zimmer

For centuries, people spoke of rabbits with horns. Eventually the stories crystallized into the myth of the jackalope--half jack rabbit, half antelope. Today, if you go to Wyoming and twirl a rack of postcards, chances are you'll find a picture of a jackalope bounding across the prairie. You may even see jackalopes in the flesh--or at least the head of one on the walls, its furry heads topped with a tiny pair of horns.

On one level, it's all bunk. It's a safe bet that the jackalope you saw on the wall or the postcard was a bit of taxidermic trickery: someone glued antelope antlers to the head of an ordinary rabbit. But, like many myths, the tale of the jackalope has a grain of truth at the center. Some real rabbits do indeed have horn-shaped growths on the tops of their heads.

In the early 1930s, Richard Shope, a scientist at Rockefeller University, heard about these rabbits while on a hunting trip. He had his friend send him some of the tissue so that he could figure out what they were made of. Shope's colleague, Francis Rous, had done experiments with chickens that suggested viruses could cause tumors. Many scientists at the time were skeptical, but Shope wondered if rabbit horns were also caused by viruses, which somehow triggered cells in the rabbit to grow in strange patterns...