Scattered across the islands of the Galápagos archipelago there are half a dozen species of lizard that rely upon a method of communication comprised of what can only be called “push-ups.” When one lizard encounters another, each takes its turn bobbing head and torso up and down in a complex and jerky system of frantic interaction. By this means, lizards of each species establish territorial authority, reinforce social hierarchies, even engage in mating rituals.
It appears that these lizards evolved from a single species settling the islands from the mainland some 34 million years ago in what scientists have identified as two major waves of colonization. A small “Eastern Radiation” left two species endemic to San Cristóbal and Marchena, while the majority of lizards have come to inhabit the southern and western islands, spreading over time to the younger islands as the older were transported eastward, eventually eroding below sea level.
Each species has developed its own particular vocabulary, its own dialect of body language, to such an extent that each species might be said to “speak a different language.” Suffice it to say, when a lizard from one species encounters a lizard from another, bobbing head and torso up and down in a complex and jerky attempt at frantic interaction, try as they might they cannot understand each other. Lizards from one island are consequently unable to interbreed with lizards from another island. Without communication, it appears, there can be no intercourse.