The special guest for the 70th anniversary programme was Sir David Attenborough. It was Sir David's fourth appearance on Desert Island Discs. An mp3 of the programme is available here.
At the start of the programme, in response to presenter Kirsty Young's suggestion that it was a staggering thought to realise that he has probably seen more of the world than anybody else who has ever lived, Sir David replied:
Well, I suppose so, but then, on the other hand, it's very salutary to remember that perhaps the greatest naturalist who ever lived and had more effect on our thinking than anybody—Charles Darwin—only spent four years travelling, and the rest of the time thinking.
Darwin's voyage around the world on HMS Beagle was closer to five years than four, but Sir David is right: a few years' ship-time was enough to inspire the greatest naturalist who ever lived (there is no ‘perhaps’ about it, Sir David!).
How many future naturalists and other scientists, I wonder, might gain a lifetime's inspiration from a few months' ship-time aboard a new Beagle?