How the cambrian exploded: Contingency in the history of science and life.

Few scientific terms are as colorful as the "Cambrian explosion": the name given to the rapid increase in animal diversity and abundance between about 540 and 520 million years ago. But for all its popularity, considerable uncertainty surrounds the history of the expression. Discussions of explosive evolution date to the early twentieth century and gained in popularity during the 1940s. Still, these discussions did not emphasize- and many did not even mention- the Cambrian Period, instead focusing on later explosions as a means of characterizing a distinctive mode of evolutionary activity. So how did the Cambrian explosion come to overshadow all other evolutionary explosions to become "the Cambrian explosion"? And how have these developments shaped discussions of the nature and significance of the event? This paper examines these questions, beginning in the nineteenth century and focusing especially on the events of the twentieth century. In doing this it illuminates the contingent history of a term- and a set of ideas- that has played an outsized role in discussions of historical contingency in biology.