"MEN ARE EASILY inspired by human ideas, but they forget them again just as quickly. Only Nature is eternal, unless we senselessly destroy it. In fifty years' time nobody will be interested in the results of the conferences which fill today's headlines. But when, fifty years from now, a lion walks into the red dawn and roars resoundingly, it will mean something to people and quicken their hearts."

These words, written by African conservationist Bernhard Grzimke in 1959, are still relevant today. Grzimke was making a plea for the preservation of African wildlife, hoping that future generations would be able to enjoy the sheer pleasure of seeing such creatures in their natural environment.

Whether Grzimke's plea will be honored is uncertain. Many species, not just in Africa but all over the world, are rapidly approaching a point beyond which...