Sir David Attenborough yesterday hit back at allegations that his latest blockbuster series, is "wildlife porn" because it does not highlight dangers to the world's environment.

The distinguished natural history broadcaster said that Planet Earth, starting on BBC1 tonight, "will help persuade people that this planet is worth conserving".

But top environmentalists say that the series, the most ambitious the BBC's Natural History Unit has ever made, has missed a vital opportunity to convey to a worldwide audience the message that humanity is driving countless species to extinction. The series, which was shot over four years and at 200 locations, contains much of the most marvellous wildlife footage ever shown.

Although Sir David has campaigned for countless environmental causes, the script he narrates says little about species at risk. The first episode opens with awe-inspiring shots of a polar bear emerging from hibernation, but does not mention, as The Independent on Sunday reported last month, that the species is threatened by global warming. It also contains unprecedented film of a snow leopard hunting, but does not say that the big cat is itself endangered by poaching and the destruction of its habitat.

Sir David told The Independent on Sunday last night, "I did not have much of an editorial input to the series, but I would defend it. It aims to show the glories of the world."