There's something uncanny about the way the BBC's natural history unit manages to so consistently set the tone for the wildlife industry. Though some might suggest a diabolical transaction may be at the heart of it, that the BBC NHU has continued to produce such notable natural history - landing five of the top 10 spots in this informal survey alone - is certainly admirable. As a demonstration of that longevity, consider that the BBC films selected here span almost three decades, from 1979's Life on Earth through to 2006's Planet Earth.

Neil Nightingale, who took up the reins of the NHU at the beginning of 2003 - 20 years after joining the Beeb - attributes that stability to two pillars: the drive within the department to re-invent the genre (and avoid the perils of resting on their laurels); and a license fee, which largely insulates the unit from the vagaries of the market. He adds that the BBC also has the scale, both in terms of slate and hired hands (it averages around 200 people) to allow it to tackle a large variety of projects and better respond to viewers and the market.

Nightingale himself produced three of the six episodes of the survey topping Private Life of Plants series in 1995. Not surprisingly, he recalls that a series on plants was a hard sell, given that it came on the heels of such popular and populist series as Life on Earth, Living Planet (1984) and Trials of Life (1990). Having Sir David Attenborough attached, however, was enough to assure dubious commissioners that the Beeb's money was not going to end up as so much compost.

The success of the series rested largely on the use of timelapse, which was a feat in the days of film. "You had no idea what was in the camera until you developed it," Nightingale recalls. "Obviously, it was often a disappointment. But when it worked, it was magical, because no one had ever seen it. The cameraman hadn't seen it."

As evidenced by reader response, the series' timelapse has since become legendary. "We were able to follow plants and construct dramatic sequences, showing plants to be every bit as exciting as animals in their predatory behaviors," says Nightingale, "their sexual behavior and their competitive behavior, and so on. People just didn't realize that was what plants were like. We hadn't entered the time scale... We tried to build up those sequences in ways that you more or less forgot about the timelapse; you just entered the time scale of plants. We saw them as creatures rather than inanimate objects."

Other minds may debate whether the series would have seen the light of day had a name other than Attenborough's been attached, but there's no debate that the filmmaker certainly casts a long shadow in the natural history realm. Five of the top 11 films readers voted for feature his credit. As Attenborough completes his final survey of the major animal groups next year with Life in Cold Blood - though Nightingale says talks have begun about a follow-on project of less scope - the proposition of an NHU without Attenborough can't help but be considered.