We humans feel very confident that we are the most intelligent species that ever walked the face of the Earth. Top of the evolutionary chain? No doubt about it. But come to think of it, how do we know that for certain?
Let’s imagine for a moment that some civilization went extinct millions of years before hominids even appeared. Although there isn’t a precise definition of “civilization,” we usually associate it with a species capable of altering its physical environment on a regional or even planetary scale. How would we know, millions of years later, that they had been here?
