After the comic malfunctions of a self-driving car, which drove its passenger/prisoner in endless circles, Unexpected Elements rounds its attention on the humble circle. Explore how one man calculated the circumference of the Earth 2,000 years before GPS was invented, then be spellbound by the Magic Circle and the mysterious woman who broke into it. And as we hit the five-year anniversary of the Covid pandemic, we take a look at the cycle of infection and mutation, before asking, 'why don’t we have one antiviral pill that kills them all?' We’re joined by evolutionary psychologist Professor Robin Dunbar, who calculated Dunbar’s number; that is, the maximum number of folks you can hold onto in your circle of friends... five? 500? 5,000? Robin reveals how many REAL friends science says you can have. Presenters: Marnie Chesterton, with Camilla Mota and Phillys Mwatee Producers: Harrison Lewis, with Alice Lipscombe-Southwell and William Hornbrook