The first time it happened was a hot August day in Maryland, the kind where the nicotine-saturated air inside the tiny, heavily air-conditioned house seemed to vie with the humidity and traffic haze outside, each competing to be more noxious than the other. Late in the afternoon, as I left for my night shift summer job, the steamy transition zone at the front door hit me with a silent thud. Sweat was already starting to bead on my back as I rolled down the windows in my Datsun.

For a modern reader, the most surprising thing about the Galàpagos Islands chapter in Charles Darwin’s Voyage of the Beagle is probably its brevity. Darwin describes the apparently recent volcanic origin of the place, runs through a quick list of its notable species, includes a figure of some finches’ beaks, and then departs for Tahiti. His entire visit to the islands lasted only five weeks, during a voyage of nearly five years.

Recently, I was talking to a researcher about a particular virus, and he mentioned that it has infected us “since fish.” Yes, fish have a time dimension. In two words, he had communicated reams of information: this virus has infected vertebrates ever since the divergence of the common ancestors of fish and mammals - somewhere around 395 million years ago. That implies that all of the species descended from those ancestors should have their own strains of the virus, which will have co-evolved alongside their host species.