No material evidence of viruses exists in the prehistoric record. Certain endogenous retroviral elements in the human genome are the closest approximation we have to fossils. It is not the preservation of an original virus, but of its echo cast through time; if we trace back the echo, we can (maybe) compress it back into something resembling the original sound. The human genome is 8 percent viral, which means that every time viruses have penetrated our germ line we have mutated in response to them. Our evolution has thus been driven in part by negotiating with viruses. They have changed us and we have changed them, and while nobody has any idea what any of this means, or where it will lead, our destinies spiral around each other, not unlike a double helix.