In fact, more than half of all the major divisions of animal life seem to have appeared in a relatively short period of time. Because many new and distinct life forms appear so suddenly in the fossil record, paleontologists refer to this period as “the Cambrian explosion.” When was the Cambrian period?

Let us assume that the estimates of researchers are accurate. In that case, the history of the earth could be represented by a time line that stretches the length of a soccer field (1). At that scale, you would have to walk about seven eighths of the way down the field before you would come to what paleontologists call the Cambrian period (2). During a small segment of that period, the major divisions of animal life show up in the fossil record. How suddenly do they appear? As you walk down the soccer field, all those different creatures pop up in the space of less than one step!

The relatively sudden appearance of these diverse life forms is causing some evolutionary researchers to question the traditional version of Darwin’s theory. For example, in an interview in 2008, evolutionary biologist Stuart Newman discussed the need for a new theory of evolution that could explain the sudden appearance of novel forms of life. He said: “The Darwinian mechanism that’s used to explain all evolutionary change will be relegated, I believe, to being just one of several mechanisms​—maybe not even the most important when it comes to understanding macroevolution, the evolution of major transitions in body type.”³³