The population of the world is growing faster now than at any other time in history. The UN projects that it will double in 60 years. Any other animal community that grows at an unprecedented rate will crash spectacularly when it exceeds the `carrying capacity' of its environment. It will run out of food and destroy its life support systems. The programme investigates the question of when the human population will reach the carrying capacity of the earth, and whether life will be worth living when it does.