Introduction

Where did the first viruses come from? They have the potential to wipe out life on Earth. But could life on Earth itself have evolved from the first viruses? Like the chicken and the egg, there are fierce arguments about which came first and rival scientists get quite cross about it all.

We take a dip into the primordial soup of creation and try to answer listener Ian's excellent question. Along the way, we revisit medieval plagues, travel to Texas to the largest urban bat colony in the world and take a walk through the dense mosquito-infested Ugandan forest that gave its name to the Zika virus.

Plus, we reveal how a virus is responsible for the placenta. No virus, no placenta; no placenta, no humans?

Do you have a question we can turn into a programme? Email us at crowdscience@bbc.co.uk

This programme has been edited since broadcast to remove a brief reference to ‘bubonic plague’ being included in a list of viral diseases.

(Photo: HIV viruses attacking a Cell. Credit: ThinkStock)