But now he’s turned into the voice of doom, warning that having large families is irresponsible and that life on Earth is going to get much, much worse as it becomes more crowded.
The veteran natural history broadcaster says that future generations face less happy and healthy lives as resources become increasingly stretched. He even predicts that natural wonders will disappear.
“I’m not optimistic about the future,” he says. “I think we’re lucky to be living when we are because things are going to get worse. In another 100 years, people will look back at a world that was less crowded, and healthier.”
It’s a horrible thought. It often seems to me that the world is way too overpopulated already. I certainly thought that on a recent visit to Dundee’s shiny new swimming pool. It was so busy it was like bobbing around in people soup.
Maybe Sir David had been there recently too, as he even seems to suggest that China’s one child policy is a good idea, although he recognises there have been human tragedies.
“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.”
So, have fewer kids and save the planet.
Try telling that to Sue and Noel Radford, who last year had their 16th child, and now have No.17 on the way. With nine daughters and seven sons, the exhausted couple have the biggest family in Britain.
They live in a nine-bedroom home which has an industrial-sized washing machine and a giant fridge to keep the mountains of food the family get through every day.
Each day they eat three loaves of bread, two boxes of cereal and consume 18 pints of milk, while an average dinner can include 16 pork chops, 15 pounds of potatoes and three cabbages.
“I love being a mummy,” she says, “we are so lucky. I get very emotional when I see the children all together.”
I would get emotional looking at them too, but with hysteria, not happiness.
Mrs Radford is clearly made of sterner stuff than me. As is my mother, who had four kids in three years and even contemplated having a fifth, until dad gently insisted that they had already done their bit to repopulate the planet – he was miles ahead of Sir David.
Mum also realised she had more than enough on her plate with my siblings and me.
Being part of a big family can be fun, there is a sense of camaraderie, of being part of a gang. It was great always having someone to play with and our games of murder in the dark were legendary.
But we were a feisty bunch and the competitiveness and fighting must have been extremely wearing for our poor parents. I remember attacking my brother with a bread knife once because he was playing his guitar too loudly.
And the arguments my sisters and I used to have about clothes would have tested the limits of a United Nations peace envoy. My big sister ordered me to remove half the outfit I was wearing when she clocked me in the local pub one Saturday night wearing stuff pinched from her wardrobe. That was considered a heinous crime in our house.
Feeding six people every day must have been soul destroying. Mum’s weekly shop must have looked like she had 16 kids, the amount we used to eat. Eventually, the biscuit cupboard had to be locked. In later life, my siblings and I were confused when we realised all households weren’t like that.
So when it came to starting a family myself I was quite happy to stick with two children. Even that is probably more than I can cope with.
There are several mums at my daughters’ school who have four children. Watching them in the morning as they drop off their charges makes me feel quite faint thinking of the work they must have already put in since they got up.
I am stretched to the limit with just two. I am usually bad tempered and frazzled as I leave them in the playground and head gratefully to the relative calm of the STV newsroom, where I work.
Friends often ask how I appear so calm presenting a live television programme, but believe me, compared to marshalling the lives of two little people being in the studio can actually be quite relaxing.