Population control, both agree, is the only way to save our environment. “There are three times as many people on earth as when I first started making television programmes,” says Sir David, “all of whom require food and a place to live. And many of us, including me, take more than our fair share. And while the answer is unclear, one thing is obvious: where women are educated and have the vote, birth rates drop.” Still he feels privileged to “be able to go where the rainforest is, not where it isn’t,” and has no plans to retire. “One day I will fall over….” “And one day I won’t be able to walk,” shrugs Goodall. “But until then,” Sir David smiles, speaking for his old friend too, “we’re enjoying ourselves.”