We may be sucking in all sorts of viruses and we really don't know the full range of them. Maybe we've got flu virus inside of us. That's a possibility. Maybe we're part flu.

We may be sucking in all sorts of viruses and we really don't know the full range of them. Maybe we've got flu virus inside of us. That's a possibility. Maybe we're part flu.

One of the big challenges now is to figure out just how many viruses there really are in the human genome. So far the estimate is 8.3% of our genome is virus, but it actually could be a lot higher.

About 1.2% of the human genome is made up of genes, things that encode for proteins, the stuff that we consider us. There is about 8.3% that's a virus. In other words we're probably about seven times more virus than we are human genes, which is kind of a weird way to thinking about yourself.

Borna virus is not a retrovirus. It doesn't actually insert its own genes into our cells. What it does is just hangs out near our DNA and uses some of the molecular machinery to copy itself.

At long last, we may be returning to the original two-sided sense of the word virus, which originally signified either a life-giving substance or a deadly venom. Viruses are indeed exquisitely deadly, but they have provided the world with some of its most important innovations. Creation and destruction join together once more.

Researchers keep identifying new species, but they have no idea about the life cycle of a given species or its other hosts. They cut open an animal and find a new species. Where did it come from? What effect does it have on its host? What is its next host? They don't know and they don't have time to find out, because there are too many other species waiting to be discovered and described.