Last night saw the final episode of what in all likelihood will be the last of David Attenborough's "sledgehammer" natural history series. Life in Cold Blood follows on from Life on Earth, The Living Planet, The Trials of Life, Life in the Freezer, The Private Life of Plants, The Life of Birds, The Life of Mammals and Life in the Undergrowth to form what must be the most stunning treatise on natural history ever broadcast, as convincing a call to the cause of conservation and testament to the unique power of television- making the remote and unfamiliar seem intimate and arresting- as one could wish for. Attenborough's voice and mannerisms wavered a little more than I'd seen before in this series. His delivery was always caricatured as hushed, but at times he seemed genuinely breathless. He also seemed to let more of his own opinions and feelings come through in the script. This felt like the end of his documentarian career and the beginning of another as commentator, even polemicist.

The final moments of the programme, as Attenborough sat in the company of "Lonesome George", the only living specimen of Pinta Island Tortoise in existence, were both poignant and weirdly metatextual. The animal is estimated to be of roughly the same age as the broadcaster; both are the last of their kind, and in the midst of their swan song. While Attenborough has suggested that we'll hear more from him on an occasional basis - and most likely on environmental issues- his globetrotting is over. The final shot, of the venerable man silhouetted in Galapagos mist, turning and disappearing amid the giant and ancient reptiles, was superb.

Attenborough's charm lies in his enthusiasm. He predates university courses in film and television and the rise of the career media luvvie. Indeed, he doesn't even have a doctorate in natural sciences. Therefore his enthusiasm is- in the strictest sense- that of the amateur, and it's infectious. He fled publishing to join the BBC back when there was no such thing as a documentary (factual programmes were called "talks", belying nascent tv's status as mere illustrated radio), much less one involving filming natural animal behaviour in parts foreign. His first forays on our screen were in Zoo Quest, a show that involved literally dragging animals out of the wild and back to the studio so the cameramen could get a decent shot at them. Said animals were then handed over to London Zoo.

Can you imagine such a show on television today? Belonging to no indoctrinated school of zoology, biology or any other -ology, Attenbrough's attitude to animals has changed and matured right along with those of the public he's sought to entertain and enlighten. We've always liked looking at them, but that enjoyment has changed from schoolboyish gawking and collecting, to a young man's perception of the natural world as a resource to be exploited, to a middle-aged appreciation of a garden in need of tlc through to this our ultimate and mature understanding of a global ecology brought to the brink by man's meddling and one that man's ingenuity must now put right if we want to continue Life As We Know It (you can have that one on me, Sir Dave). He hasn't needed a wheedling Greenpeace beardy to brow-beat him into toeing the lefty line; he's been around the damn planet often enough to know that something's up. How lucky that we've been able to join him in part, and have him point out all the most exciting sights.

I've touched on this before, but who can replace him? It's impossible to imagine any other voice currently heard on the BBC talking with even a tithe of Attenborough's authority on matters furry, scaled and slimy. Nigel Marven's blown what little credibility he had with his ridiculous cgi dino-wanks. That and he's as much screen presence as a sea cucumber. Alan Titchmarsh? I'd rather not have my natural history dished out by hands that write porn for grannies, thanks. Who else? Bill Oddie? Too nerdy. Michela Strachan? Too sentimental. That posh bird who looks a bit like Katie Melua? No. Simon King, maybe. Or bring back Julian Pettifer!