This is a story about a group of people who are trying to alter the course of human behaviour. It is also about human beings' most primitive attitudes to the matter we are all descended from: the mud, the sludge, the dirt. It's about the way we raise our children, and how the work these people are doing challenges us to re-examine the way we learn about the world around us. "It is," says the Frenchman at the centre of the project, "all about the future of human beings and humanity."
It is also a story about a washing-powder advertisement.
Where shall we begin? In Victorian England, perhaps, where the belief that cleanliness is next to Godliness was first propounded. The alliance between medicine and morals found its apostle in Florence Nightingale, in whose Crimean wards the links between bacteria and illness - and thus between purity and health - were rigorously tested.
Let's zip straight on to the TV studios of 1950s America. That's when washing-powder advertisements came to dominate the ad breaks. The soap powder companies were among the first advertisers to embrace the new medium, and the embrace has remained firm and loving over the succeeding decades. The battle between two manufacturers, Unilever and Procter & Gamble, dwarfed the lesser rivalries of Coke and Pepsi, McDonald's and Burger King.
P&G (owner of Ariel, Dreft and Lenor, among other brands) has maintained the edge in the most significant markets - 35 per cent versus 19 per cent in Europe, 60 per cent over 17 per cent in the US - according to J P Morgan. Its rigorous approach to the science of selling cleanliness puts it at the head of arguably the most revered army of marketers in history. This is the company that pioneered before-and-after shots, window tests (displaying the brilliance of its whites against outdoor light), doorstep challenges and the killer innovation - biological powders, powerballs and liquids. The chattering classes in the ad agencies winced at the hard-sell relentlessness of the P&G culture. Feminists rebelled at the way women - housewives, rather - were portrayed. (P&G's ads, invariably featuring friends and neighbours competing for whiter whites and shinier kitchen floors, became mockingly known as the "two Cs in a K" school; those with less than pure minds can spell it out for themselves.)
Underlying the science and the obsessive research that typified P&G's approach was one devastating psychological ploy: if you make women feel guilty about dirt, and paranoid about the cleanliness of their houses, they will buy. I'd happily take another 10,000 words to discuss the use of paranoia in the media to boost sales, ratings and circulations. Let's focus instead on what Unilever (owner of Persil, Omo, Surf) has now done to retaliate.
Since 1998, the London-based agency network, the Lowe Group, has been working on a new strategy based on the premise that "Dirt is good": three words that fly in the face of 150 years of social conditioning. The campaign has just been launched in Europe, Asia and Latin America. The script, written by Lowe's Adrian Holmes (brother of the literary biographer Richard Holmes) is a combination of British Airways' celebrated "Eye" commercial and Lord of the Flies. A group of children, unsupervised, play on a beach. They do things kids do on a beach - build dams, get soaking wet and, of course, filthy. At the end, we see from the air that they have created a huge picture of a whale. It's a simple enough narrative, but the voiceover carries the punch: "Kids think differently about getting their clothes dirty," it intones. "From today, we invite you to do the same. We believe dirt is good."
Pierre-Emmanuel Maire, Lowe's global communications director for Unilever, has been involved in developing the strategy from the beginning. "We have read tons of material, studying how human beings develop," says Maire. (He has also had plenty of opportunity to see how the research works in practice - he has three children under the age of nine.) The thinking that Lowe presented to Unilever was more far-reaching than any political think-tank's paper on the way human beings act in society.
The seismic movement identified by the Lowe researchers is, in Maire's words, "the death of the computer kid". That kid - deodorised, sanitised, biologically washed, cooped up in a spotless bedroom in front of a computer - has become a nightmare figure for many parents. They want kids who get out with other children, explore, interact - and maybe get dirty in the process.
At the end of the Nineties, a new slant on the science of hygiene added to the unease about the sealed-off world of the computer kid. The British Medical Journal published research by Italian immunologists early in 2000 which suggested a link between childhood allergies and excessive hygiene. The research is too detailed to go into here, but its thrust - that we need contact with bacteria to strengthen our immune systems - was leapt upon enthusiastically by campaigners, including the National Asthma Campaign.
The research has made sufficient headway to encourage the Unilever team. But this is still advertising, not social engineering. What's in it for Unilever? Simple. The more you allow your kids to get dirty, the more you'll need to wash their clothes.
But Maire, for one, is cheerfully prepared to alternate the role of philosopher and hard-nosed marketer. "We are onto a big piece of truth," he says. "But it's not bad business, either."