Fungi are an ancient form of life, existing long before the first amphibians, reptiles or mammals roamed the planet. There are estimated to be well over 1 million species of fungi worldwide – some can be poisonous and destroy trees, others can be very healthy to eat or can help crops absorb nutrients. Despite several mass extinction events, fungi are the one form of life that always survive, and in this episode, Jonathan investigates what ancient fungi can tell us about historical climate events and how studying them might help us predict what will happen in our planet's future due to climate change.

The human immune system is amazing, consisting of a variety of cells all working together to identify and destroy invading cells and protect our bodies from infection. Unfortunately, in some cases, the immune system is unable to distinguish one from the other and begins to attack healthy cells.