Sir David Attenborough investigates whether the world is heading towards a human population crisis. It's a disturbing question; how many people can live on planet earth?
Sir David Attenborough reflects on the profound effects of population growth.
Simon Reeve navigates along the Tropic of Cancer in this series of images.
Photos from Tribal Wives; the ultimate wife swap!
A gallery of photos from the incredible human natural history series Human Planet.