Slate, December 6, 2012
To understand what it means to be human, you have to understand koalas. Or, to be more precise, you have to understand how they are dying from a bizarre viral outbreak that has been raging for the past 150 years or so. The koalas are now going through something our ancestors experienced 31 times over the past 60 million years. And those ancient viral outbreaks have helped to make us who we are today.
Australian biologists discovered the koala outbreak in 1988. They were examining the blood of a koala dying of leukemia when they came across a virus infecting its white blood cells. The koala retrovirus, as it is now known, made its hosts sick in much the same way the feline leukemia virus sickens cats. It inserted its genes into host immune cells, which then produced new viruses. The infection also caused the cells to replicate at a frenzied rate. Once the scientists had found the koala retrovirus in one koala, they looked for it in others, and they soon found it all over the koala’s range—the entire eastern side of Australia.