The answer to this can be found in Chapter 1. In this context, the term "great leap forward" refers to a time at which human beings (for whatever reason) experienced a dramatic advance in their social development. This was a time when technology as well as cultural expression grew much more quickly than it ever had to that point. This happened sometime around 50,000 years before the present. In a sense, this is when the human species truly became human. Shortly after this great leap forward, modern human beings began to leave Africa and to colonize the rest of the world.