Abstract
About 540 million years ago, a rapid radiation of animal phyla radically changed the Earth’s biota in a
geological eye-blink. What caused this “Cambrian explosion”? Over the years, paleontologists have
pointed to a wide array of different physical mechanisms as the causal “trigger” for the explosion. More
recently, some paleontologists have proposed complex causal pathways to which multiple physical
mechanisms are said to have contributed. Despite their variety, these answers share an assumption that a
single explanation can in principle be constructed that identifies some factor or confluence of factors as
the cause of the Cambrian explosion. That assumption is unjustifiable. The Cambrian explosion had
multiple causes, and different aspects of the event are best explained by different causes. These different
causes cannot, even in principle, be integrated into a single causal explanation. We can learn much about
the causes of the Cambrian explosiondor for that matter about any historical eventdbut only by
attending more carefully to how we frame our causal questions about the past.