In early human history, the main function of mental models was most probably that of fostering human environmental adaptation. Mental simulation capacity made it possible to predict the behavior of other humans and to plan and organize complex action sequences, such as large animal hunts. Yet, if the models available to those early humans had remained only mental models, we likely would not have progressed much from prehistoric to modern times! At one point during human evolution, humans began to externalize their own mental models and share them with their companions, launching the "cognitive revolution" of the upper Paleolithic period (40,000–10,000 years ago) thereby. Some anthropologists believe that this change was due to enhanced working-memory capacity (Coolidge and Wynn 2005), which allowed for the growing use of spoken language and tool construction as well as the beginnings of new forms of language, such as rituals, visual arts, and music. Several millennia later, humans began to wonder about the relations that might exist between their symbolic creations and reality. For example, Plato described the cognitive role of models or "paradeigmata" ("παραδείγματι") in his dialog "Politicus' (the Statesman). One of the characters therein referred to the model of the weaver to illustrate the nature of the statesman and compared his method to that of weaving various fibers to create a single fabric. More generally, Plato described the usefulness of models in terms of a process that involves identifying similarities and differences. When examining the conceptual similarities and differences between a model and a phenomenon under examination, people transform their initially confused and approximate ideas into more precise and rigorous comprehension. As described in the following chapters, this is also what occurs when students compare their own mental models of a system to a simulation model.