The image above illustrates several aspects of the evolution of the hominid/human face and skulls over several million years. Perhaps the most obvious trend visible from these three skulls is the emergence of a forehead, a development related to increasing brain size, especially the forebrain or cerebrum. But along with that feature is a gradual change in the angle of the face from a backward sloping into a nearly perpendicular, straight up and down plane. 

The chin, which appears only with modern Homo sapiens, is less easy to account for. It may be a development associated with the emergence of language and speech, which required modification of the throat and mouth. To facilitate speech, humans evolved a larger resonating column in the throat above the larynx. 

Note that while we are the only creatures with fully developed language, humans are also extraordinarily well equipped to send non-verbal messages. 

The human face then, indicates a great deal about our way of life as a species. Our way of life is communal and interactive to a degree rare in other creatures. Complex acts of communication – the sending and interpreting of finely shaded and subtle messages, either through language or "body language" and expression – are central to our way of life. The skulls above thus illustrate, in addition to increases in brain size, the gradual evolution of a complex social life.