Will robots take our jobs? It's an age-old question.

Ever since Homo erectus, or upright man, a type of early human, carved a piece of stone into a tool, the welfare of our species has been on the increase. Indeed, this technological breakthrough led first to the hand ax, and eventually to the iPhone. We have found it convenient to organize the most dramatic periods of change between these inventions into four industrial revolutions. As each revolution unfolded, dire predictions of massive job losses ensued. Looking back at the first three, we can see how the concerns were misplaced. The number of jobs increased each time, as did living standards.