Mankind will itself become an endangered species if we ignore environmental problems, Prince Charles warned in a speech.\"We are, of course, witnessing what some people call the sixth great extinction event...,\" he said in a speech in London, as he assumed the presidency of Britain\'s branch of the World Wide Fund for Nature (WWF).\"The earth is being depleted of many of her natural resources, from top soil to fish, and if we carry on as if it\'s \'business as usual\', we will receive dangerously diminishing return from nature\'s capital that will begin to threaten our very survival,\" he added. Britain\'s heir to the throne takes over the role at the WWF from Princess Alexandra, the queen\'s cousin, who held the post for almost 30 years. His own father, Prince Philip, was the organisation\'s president in the 1980s and 90s before taking over the presidency of the WWF International. Charles has been a long-time campaigner on green issues, provoking criticism from some observers who argue he is exploiting his status. But he argued: \"None of us must be afraid to stand up and be counted... \"Despite all the brickbats, all the doubts, all the despair at the state of the environment... I have learnt that when people come together, positive change is possible,\" he concluded.