Theories are inferred from observations of organisms and objects. How can we critically approach a new theory? For example, a theory that sometime in our evolutionary past a chimpanzee mated with a pig and produced a hybrid – our ancestor! (Incidentally, that study was published around the time of “piggate” scandal.) Or what about an aquatic ape theory which suggests that our ancestors lived in water for a while? A piece in The Guardian on the aquatic ape theory has inspired me to create this simple graphic. The goal was to produce a mini-guide of critical thinking about theories, not only biological ones but also others, the mad ones like UFO or Loch Ness monster and the well established ones like gravity or evolution and any new proposals. Try the mini-guide for yourself and let me know what you think.