The running joke in AI circles that every time a computer manages to do something we previously thought required human-level intelligence, we raise the bar and define this something to be what intelligence is not. Fundamentally, I believe that intelligence is the capability of a system (biological or computerized) to dynamically adapt to its environment. You might be surprised to find out that some viruses are able to navigate inside host cells and express different genes (change their behavior) based on where they are inside these host cells.