This week, we’re skipping to the tail end of the digestive tract, to learn some fascinating facts about feces. Rachelle Saunders welcomes science journalist Maryn McKenna back to the show to discuss human gut bacteria, and the biome-boosting power of fecal transplants. Desiree Schell speaks to anthropologist Cecil Lewis about what studying ancient poo can tell us about the evolution of the human microbiome. And Rachelle speaks to zoologist Eric Warrant about how some species of dung beetles can navigate by the light of the night sky.