In 2005, when he was about to turn 80, Sir David Attenborough made a surprise announcement. His next blockbuster, Life in Cold Blood, would be his last major television series.
After that, he would retire, coming back only for the odd voiceover or one-off. Yet eight years later, to the relief of natural history fans, Attenborough's prodigious TV output shows no sign even of slowing down, let alone stopping.
"I am the luckiest soul I can think of," says Attenborough.
"I am 87, and I know a lot of people who are 87, good friends of mine who are 87, who can't get out of a chair.
"And it's not because they're evil, or done bad things ... they're great people. It's just - I'm lucky. And it would seem almost ungrateful not to be doing it, if you can do it."
In person, it's clear Attenborough is far from past it. Sharp and spry, he wears chinos and an open-neck shirt, and rimless glasses that are charmingly skew-whiff on his nose. As he enthuses about a series of topics his professorial hair is just a little wilder than it usually looks on TV.
And Attenborough's contribution to his new BBC show is much more than just the voiceover. Labouring under the title David Attenborough's Rise of Animals: Triumph of the Vertebrates, the two-part documentary sees him travel around the world, tracing the evolution of creatures with backbones. In China, he becomes the first person to film two fossils that have filled crucial missing links in that evolutionary chain.
One of them provides the evidence that dinosaurs really did grow feathers and evolve into birds - as scientists have long suspected. "Most fossils that you find are bones - feathers don't fossilise, because they decay very quickly," he says.
"The point about the Chinese deposits is that the dead bodies fell to the bottom of the lake, and were covered very quickly, before they decayed. They discovered the bones of a small dinosaur - and the perfection of the fossilisation was such that you could see the actual feathers."
The other remarkable fossil preserves the moment when the very first mammals evolved, 195 million years ago. Just 1cm long, the skull of the tiny "hadrocodium" shows that its brain was huge, compared with the rest of its body. It was also warm-blooded, and covered in fur.
"That was a knockout, I couldn't believe it," says Attenborough. "Of course, when you hold it, you felt that if you drop it, it could go down between the floorboards. I'd be the man who lost hadrocodium."
For a British film crew to be so warmly welcomed into the impenetrable world of Chinese palaeontology must, I suggest, be down to Attenborough's global star power. But he is having none of it.
"I think they thought, 'Thank God - here's somebody who doesn't necessarily want to attack us politically, and is interested in an animal apart from the giant panda'," he says. "The Chinese don't know who I am from a hole in the ground."
He laughs and, putting on a Chinese accent straight from a Peter Sellers comedy, he repeats: "Ho-ah in the glound!" It's a moment of well-meaning fun - but also a dab of political incorrectness that would make his BBC commissioning editors flinch.
For his part, Attenborough also relishes the chance to have his say on some controversial topics - ones that other BBC presenters might swerve.
He has recently made headlines by suggesting that advances in medicine, which mean even the weakest babies usually survive, have effectively stopped human evolution.
He is also strident about the need for human population control, saying "we are heading for disaster unless we do something". But he is instantly alert to the "huge, huge sensitivities" around his opinion.
"To start with, it is the individual's great privilege to have children. And who am I to say that you shan't have children? The next thing is a religious one, in the sense that the Catholic Church doesn't accept this - that you should control the population.
"And the most tricky of all, when you talk about world population, is the fact that the areas we're talking about are Africa and Asia. To have a European telling Africans that they shan't have children is not the way to go about things."
Sensitivities or no, Attenborough is very clear that unless humans control their population, the natural world will - indeed, has already started to - fight back. "What are all these famines in Ethiopia, what are they about?" he says.
"They're about too many people for too little land. That's what it's about. And we are blinding ourselves. We say, get the United Nations to send them bags of flour. That's barmy."
Such clear and fearless thinking is bound to be controversial. And, unlike his 79-year-old self, Attenborough has no plans to stop speaking out.
He already has two more TV projects on the go, both made in 3D for Sky. One will take a 90-minute tour around London's Natural History Museum at night, and the other is a two-parter called Conquest of the Skies. But even Sir David can't go on for ever - and, when he was honoured at a BBC Radio Times magazine event last year, he was tempted to name a successor to his crown.
"I didn't do any anointing," he says, good-naturedly but firmly. "It was a total surprise to me when Professor Brian Cox got up and gave this great eulogy [to me]. So I said, well thank you very much - and, if I had a torch for science programmes, I'd hand it on to you ... I should have added, 'But not yet, professor!"'