Abstract

I argue that a critical feature of language that distinguishes it from animal communication isdisplacement,the means to communicate about the non-present. This implies a capacity for mental travels in time and space, which is the ability to call to mind past episodes, imagine future ones or purely fictitious ones, and locate them in different places. While mental travel in time, in particular, is often considered to be unique to humans, behavioral and neurophysiological evidence suggests that it is evident in some form, at least, in nonhuman animals, including rodents, and may go far back in the evolution of animals that move. The linguistic capacity to share experiences that transcend space and time evolved much more recently, accelerating during the Pleistocene with increasing demands for effective cooperation and long-distance planning. The expansion of mental time travel probably co-evolved with the development of language itself, because the sharing of memories, plans, and stories vastly added to our own individual experiences. From this perspective, the critical period of the Road Map runs from the emergence of the genusHomoaround 2 million years ago to the present.