A conversation with Forrest Bishop about the Pleistocene Murders - a whodunnit theory that seeks the cause of the megafaunal extinction that rocked the planet during the most recent period of glaciations - from 2.5 million years ago to about 10,000 years ago. While most theories - including a recent paper from Tel Aviv university point the finger at increasing populations of hungry humans, Forrest proposes that this ignores a crucial, global change that occurred over the course of the Pleistocene: a global decrease in carbon dioxide levels.   In the Pleistocene Murders, he proposes that falling carbon dioxide levels led to the dominance of c4 plants - those who can flourish at relatively low partial pressures of CO2. This evolutionary advantage allowed grasslands to dominate the globe... which, in turn, led to a decrease in the caloric content of the trophic foundation of the world's ecosystems. It's an excellent story that binds together geology, chemistry, and biology... and even a little bit of spirit, as humans have an emergent role on the planet that we get to at the very end of the conversation