Sir David Attenborough does not believe that an understanding of evolution is incompatible with faith in God, he will tell Radio 4 listeners on Sunday.

Attenborough, who was invited back to Desert Island Discs to mark the 70th anniversary of the radio programme, explains that, while he is still agnostic, he does not rule out the possibility of the existence of a deity.

"I don't think an understanding and an acceptance of the 4 billion-year-long history of life is any way inconsistent with a belief in a supreme being," the 85-year-old broadcaster and writer will tell presenter Kirsty Young. "And I am not so confident as to say that I am an atheist."

Attenborough will also tackle the controversy over the use of footage of polar bears filmed in a zoo in his recent television series, arguing it was the job of the film to give as full a picture as possible of the animal's life cycle.

Attenborough, who will choose to take a piano with him to the deserted island, recalls his childhood in Leicester with his "formidable" father, mother, and three brothers. He will also recount how his family adopted two new family members, both German Jewish refugee girls.

"My parents said, 'You now have two sisters'," says Attenborough. "And I thought 'hang on, you are my parents, I am not sure I want to share you'."

Attenborough's musical choices for the desert island include the theme from Zoo Quest, his first television show about the natural world, and part of Handel's Messiah.

The broadcaster will also recall how his brother, Sir Richard Attenborough, the renowned actor and film director, forced him to take part in amateur dramatics. "Dick put on shows and recruited me as a spear-carrier for the dumb parts," reveals Sir David.

Young will remind Attenborough that, in his first appearance on the show in 1957, he said his ambition was to climb Mount Everest. "I wouldn't make it to base camp now," he says. "Back then I thought it was the only thing a red-blooded young Englishman should do."