Even those who say they never watch television admit to watching the natural history programs of Sir David Attenborough.

In 2002, Attenborough marked 50 years of broadcasting with the BBC. And as 60 Minutes first reported last November, that's 50 years during which this modern day explorer has roamed every corner of the earth to produce what is considered to be some of the best television ever made.

In those programs, one of Attenborough's favorite techniques is to begin a sentence on one continent, and complete that sentence on another continent.

Correspondent Ed Bradley reported from Mali, a country in West Africa on the edge of the Sahara desert.

If you've ever wondered where Timbuktu was, all you'd have to do is head up the Niger River and you'd soon be there.

60 Minutes came to Mali to find David Attenborough, 75, hard at work on a new series of natural history programs.

What was Attenborough doing on the banks of the Niger? For thousands of years, African tribes have driven their cattle across the river to find new grazing lands, and Attenborough was here to film the crossing and to explain how human beings first domesticated animals.

What you first notice about him is that the enthusiasm you see on the screen is for real. After 50 years, Attenborough is still fulfilling his boyhood dream.

"I was pretty sure I wanted to be investigating the natural world in some way," says Attenborough. "I collected all the things as small boys do - keeping tanks of fish and keeping grass snakes and you know, all that. And I keep doing it."

Each of the Attenborough series takes about three years to make, and they all start here at his home outside London with a script that he writes himself.

"I write the scripts as though anything is possible, anything," he says.

And it seems anything is possible. Thanks to the technical skills of BBC's natural history unit filmmakers who work with Attenborough, we've been shown things that we've never seen before.

Sometimes those filmmakers need not only skill but also courage. For instance, to get shots of a killer whale hunting seals in Patagonia, the cameraman laid down in the attack zone.

"It's an astonishing sequence and I wasn't there when it was done," says Attenborough. "I mean, it's an example of the bogus credit which people like me, anyway, continually get, because it's the cameramen who get these astounding shots."

But it's Attenborough's talent as a communicator that makes his programs come to life.

The hushed tones that he adopts in the presence of wild animals like mountain gorillas in Rwanda have become a well-known trademark in Britain.

"The press say, you know, 'Oh the Old Whisperer.' But all I can say is if they were sitting within a couple of yards of a gorilla you don't actually say, 'Well, here I am sitting,' you say, whispering, ' Here I am,'" says Attenborough. "It's partly because you don't want to frighten the animal, but it's partly a kind of respect."

But those gorillas gave Attenborough a welcome he didn't expect.

"The female, a huge big thing, put this great hand like a boxer's glove on top of my head and sort of looked me straight in the eyes," he says, pleased with the gorilla's reaction. "It was the fact that somehow I had escaped the human condition. I mean there's this animal that could tear me apart, rip my arms out of their sockets and all she does is want to look in my eyes. That's OK."

Attenborough started his career back in the early days of black and white television and in the '50s and '60s made dozens of natural history films. But then in 1979 came "Life on Earth," a series about how life evolved on this planet. An estimated 500 million people around the world watched "Life on Earth" and the BBC realized that in Attenborough they had a rare and valuable species.

Over the last 20 years, he has been given a free rein to go wherever he wants, to do whatever he wants, and Attenborough has gone everywhere. He has searched for natural life, from the top of the tallest trees in the Amazon Rainforest, to the depths of the oceans, from the hottest place on earth, to the coldest.

And sometimes the creature he's looking for appears right on cue. Take, for example, the Emperor penguin.

"That was just luck. I was able to walk up to him and he just stood there," says Attenborough. "I think he'd lost his way. You know how penguins are, they don't look the brightest of birds, do they? Sort of standing around."

But not all animals are as pleased to see Attenborough as he is to see them. And there's one animal he doesn't like at all: rats.

Rats were what he had to face in a Hindu Temple in India, where they're considered sacred and allowed to swarm all over the place.

"The director says don't worry, he said, 'We'll put you on a stool so the rats simply, they'll be, they'll all be swirling around you, but they'll be no bother,'" he says.

But even perched on a stool the normally unflappable Attenborough was put off his stride: "If you think a rat is about to climb up your trousers it is very difficult to look at the camera and keep on going, isn't it?"

Particularly if you've got to whisper in a very controlled voice.

"That's right," he says, laughing. "If they gave us a pair of pliers … and a felling axe."

Attenborough says that he used to make up for the food he has to eat on the road by bringing along some chocolate.

"But about six months ago I suddenly was aware that these well-known khaki pants were no longer buttoning as loosely as they might. So I gave it up," he says.

How does he do with clothes on the road? He's got eight identical blue shirts and four khaki pants.

"I always wear the same thing, so you can walk into the jungle that you shot in Costa Rica and out of the jungle which was in the Congo and you look exactly the same," he says.

And he admits that he also dresses this way at home. But even Attenborough dresses up when he goes to Buckingham Palace to see the Queen. His work for conservation – he is a founding member of the World Wildlife Fund – has led to a knighthood and many other awards.

But Attenborough is careful not to preach conservation in his television programs: "The most important job is persuading people that the natural world is complex and wonderful and one of the most precious things we have. And if you're going to do that, and every time you do it, you show the facts, you end up by saying, 'And it's all disappearing and it's all your fault,' people will stop viewing."

soon discovered that shooting natural history programs involves a lot of just waiting around. Attenborough uses the down time on the road to listen to music - one of his great passions.

For his series "The Life of Birds," he clocked 256,000 miles - the equivalent of 10 times around the earth.

For most of his career, Attenborough managed to combine the long periods away from home with a happy family life. He married in his early 20s, and the best man was his older brother, Richard, the actor and film director. He and his wife Jane raised two children. But now, the home in London to which he returns is no longer where his heart is. Five years ago, when he was in New Zealand, Jane suffered a brain hemorrhage and he rushed home to her bedside.

Is it tougher to come and go now that she's gone?

"No, it's easier. The magnet isn't there," he says. "The magnet's not in London. Before, you wanted to get back to see her and be with her and so on and of course that doesn't apply any more so you might as well be here than there. Not quite, because home is home and there's all your things and so on, but it's not as it was."

Does he ever ask himself why we're here? And if so, does he have an answer?

"I don't know. People sometimes say to me why don't you admit that the humming bird and the butterfly and the Bird of Paradise are proof of the wonderful things produced by creation. And I always say, 'Well, when you say that you've also got to think of a little boy sitting on a riverbank like here in West Africa that's got a little worm, a living organism, that's in its eye and boring through its eyeballs and is slowly turning it blind. The creator God that you believe in presumably also made that little worm,'" he says.

"Now I personally find that difficult to accommodate and so therefore when I make these films I prefer to show what I know to be the facts. What I know to be true. And then people can deduce what they will from that."

When David Attenborough left Mali, this was just the first leg of an exhausting three-day journey to an even more remote part of Africa, where another BBC crew and a colony of hyenas were waiting him.

So how would Attenborough like to be remembered? "I imagine every human being in the world cannot but be appalled by the prospect that you might be slowly reduced into senility," he says. "I mean that's dreadful humiliation it seems to me."

So, he says, clicking his finger, "One hopes. I was going to say, 'God willing.'"

No sooner did he finish his series, "Life of Mammals," than Attenborough began a new three-year epic production. Last week, he told 60 Minutes that he's hard at work on a series called "Life in the Undergrowth," which he says is going to be all about scorpions and spiders.

