Psychologist Kimberley Wilson and Dr Xand van Tulleken take a journey around the human body, to find out what it can tell us about our innate capacity for change. In this episode, Kimberley and Xand zoom in on the appendix, long written off as a useless body part. But new research reveals that this worm-shaped part of our digestive system can actually tell us a lot about human evolution, and the relationship between brain and body. Xand and Kimberley find out the surprising truth about what the appendix actually does, hear how it might be implicated in neurodegenerative diseases such as Parkinson's disease, and peep behind the curtains of a nightmare appendectomy. Producer: Dan Hardoon Executive Producer: Kate Holland A Whistledown Production for BBC Radio 4