Sir David Attenborough has said that he is not optimistic about the future and that people should be persuaded against having large families.

The broadcaster and naturalist, who earlier this year described humans as "a plague on Earth", also said he believed humans have stopped evolving physically and genetically because of birth control and abortion, but that cultural evolution is proceeding "with extraordinary swiftness".

"We stopped natural selection as soon as we started being able to rear 90-95% 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," he tells this week's Radio Times.

"Stopping natural selection is not as important, or depressing, as it might sound – because our evolution is now cultural … We can inherit a knowledge of computers or television, electronics, aeroplanes and so on."

Attenborough said he was not optimistic about the future and "things are going to get worse".

"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.

"We may reduce in numbers; that would actually be a help, though the chances of it happening within the next century is very small. I should think it's impossible, in fact."

The broadcaster, who is a patron of the charity Population Matters, which promotes family planning and campaigns for sustainable consumption, also appeared to express qualified support for the one-child policy in China.

He 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."

He added: "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. But I'm not particularly optimistic about the future. I think we're lucky to be living when we are, because things are going to get worse."

Attenborough's next screen venture, a two-programme study of the rise of animals, begins on BBC2 on 20 September. The BBC has already announced future projects involving the much-loved face and voice of natural history. "If I was earning my money by hewing coal I would be very glad indeed to stop," said Attenborough, who had a pacemaker fitted to regulate his heart in June.

"But I'm not. I'm swanning round the world looking at the most fabulously interesting things. Such good fortune."

He also told the magazine: "I'm luckier than my grandfather, who didn't move more than five miles from the village in which he was born. I have all kinds of pleasures and luxuries that I appreciate and I'm very, very fortunate. I think that applies to the majority of people – in this country, at any rate.

"But I think that in another 100 years people will look back at a world that was less crowded, full of natural wonders, and healthier."