Climate change may have contributed to the fall of North America's first and largest pre-European city — and the proof may be in the poop, researchers said this week. A new study published in the journal Proceedings of the Natural Academy of Sciences details how fecal records linked to Cahokia, one of the most prominent agricultural sites in North America, gives clues into how declining precipitation and serious flood events may have impacted the population of the city, which is located outside of modern-day St. Louis.