Human beings have stopped evolving and should be persuaded not to have large families, Sir David Attenborough has said.

The TV naturalist, 87, said he was not optimistic about the future and "things are going to get worse".

He said he did not believe humans would become extinct, but told the Radio Times: "I think that we've stopped evolving.

"Because if natural selection, as proposed by Darwin, is the main mechanism of evolution - there may be other things, but it does look as though that's the case - then we've stopped natural selection.

"We stopped natural selection as soon as we started being able to rear 95% - 99% of our babies that are born.

"We are the only species to have put a halt to natural selection, of its own free will, as it were."

The broadcaster said of the future: "I don't think we are going to become extinct.

"We're very clever and extremely resourceful - and we will find ways of preserving ourselves, of that I'm sure. But whether our lives will be as rich as they are now is another question."

Speaking about the one-child policy in China, Sir David said: "It's the degree to which it has been enforced which is terrible, and there's no question it's produced all kinds of personal tragedies. There's no question about that.

"On the other hand, the Chinese themselves recognise that had they not done so there would be several million more mouths in the world today than there are now.

"If you were able to persuade people that it is irresponsible to have large families in this day and age, and if material wealth and material conditions are such that people value their materialistic life and don’t suffer as a consequence, then that's all to the good."

The broadcaster, who is presenting Rise Of Animals, a two-part documentary on the ascent of man on BBC2, had a pacemaker fitted in June, but described the operation as "no big deal".

"When you're in your 80s, your heart gives you a funny five minutes every now and again and they won't insure you unless you have a cardiologist to say that you can go on a long-haul flight. So I had to have the pacemaker," he said.

The wildlife star, who previously had a knee replaced, said of the possibility of retiring: "I don't think so. If you've got a motor car and its brakes fail, and you have the capacity to replace them, you replace them. And we have the capacity to replace knees, which is wonderful."