In this lecture I trace the major events in human physical and cognitive evolution over the last 4-plus million years, with an eye to asking the question "how and when did we become fully human?" Of course, humanity is an ill-defined concept, but it is clear that fully modern human cognition is a recent acquisition in our lineage. The human story has largely been one of highly sporadic innovation, with the appearance of important behavioral and physical novelties being relatively rare events, separated by long periods of stasis. Further, the appearance of new behavioral innovations cannot be "explained" by the appearance of new types of hominid, since there is no correlation between these two distinct phenomena, either in time or in space. For the most part, new types of hominid, throughout hominid history, can best be characterized as doing what their predecessors had done, if perhaps a little better. It is only with the arrival of behaviorally modern Homo sapiens that a radically new type of human came on the scene, with consequences for the history of the biota that are still reverberating. The key innovation that the first well-documented behavioral moderns (the "Cro-Magnons" of Europe) brought with them appears to have been that of symbolic reasoning and thought. This new capacity is amply demonstrated in the archaeological record that these people left behind, which includes for the first time cave painting, engraving, carving, bodily decoration, notation, music (as seen in bone flutes), elaborate burial with grave goods, and a host of other behaviors. Since anatomically modern humans had already been co-existing with Neanderthals for some 60,000 years when these innovations were made, the inevitable conclusion is that an emergent capacity of the human brain had become established for unknown reasons, and was later released by a cultural stimulus. The best candidate for a stimulus of this kind is the invention of language. In terms of overall phylogenetic pattern, humans are no different from any other successful group. Our evolution was not a gradual linear process; rather, it was an eventful story of evolutionary experimentation, with new species constantly generated, and regular extinctions taking place. It is an unusual thing for us to be the lone hominid in the world today.
