The second part looks at man's potential effect on the world's areas of wilderness. As the human population has grown, only a quarter of Earth's land now remains uninhabited (aside from Antarctica). Although around 12% is protected, this may not be enough — providing such places are not just 'enclosures' and bordering territories are also managed. Ethiopia's Semien Mountains are increasingly encroached upon for farming land, and this example leads to the question of overpopulation. Some interviewees argue that it is not just about numbers: how humans consume their natural resources is also important.

• George Fenton