a BBC Cymru Wales Drama Production ; executive producers, Brian Minchin and Steven Moffat ; directed by Jamie Payne ; written by Steven Moffat ; produced by Marcus Wilson
narrated by David Attenborough ; producer, Justin Anderson ; series producer, Karen Bass ; a BBC/Discovery Channel co-production in association with Wanda Films ; BBC Earth
BBC Earth ; narrated by David Attenborough ; producer, Tom Hugh-Jones ; series producer, Rupert Barrington ; a BBC/Discovery Channel/France Televisions/Open University co-production