Tom Sutcliffe discusses evolution and extinction with Jules Pretty, who's been travelling to meet "enduring people in vanishing lands" and is concerned about their future; with Andreas Wagner on solving what he calls evolution's greatest puzzle - how can random mutations over a mere 3.8 billion years solely be responsible for eyeballs; poet Ruth Padel on what we can learn from animals and Chris Stringer who's been looking at ancient human occupation of Britain and how homo sapiens may have driven other humans to extinction.