The documentary film 8 Billion Angels opens with majestic footage of farmers tilling the land, factories billowing smoke, traffic-choked highways, city streets teeming with people, and a voiceover by the primatologist and conservationist Jane Goodall. “What I really, really, really would love to change, without causing pain or suffering: reduce the number of people on the planet,” she says, “because there’s too many of us. It’s a planet of finite resources and we’re using them up. And that’s going to cause so much suffering in the future.” With these words, she sums up the driving argument of this grand, sweeping documentary, produced by the environmentalist Terry Spahr. The film maintains that there is a simple solution to climate change, environmental destruction and mass extinction: to protect the planet and each other, we need to have fewer children.