Suicidal lemmings and other scientific myths

A slip of a nutritionist's pen and Popeye, the 1930s cartoon, lie behind spinach's ill-founded popularity with parents.

So now we know: lemmings don't commit mass suicide after all. Contrary to popular belief, these furry inhabitants of the arctic tundra do not suddenly lose the will to live, head for the coast and hurl themselves into the sea. But they can end up taking a fatal swim in their search for new habitats following sudden surges in population. At least, that's what Professor Tim Coulson of Imperial College, London claims is the truth behind the legend of lemming suicide, in an article in the current issue of the top science journal Nature. Yet the origins of the legend is itself the subject of another myth - one which points an accusing finger at a wildlife film made by the Disney corporation half a century ago.

Called White Wilderness, it purported to show lemmings tumbling down coastal cliffs in a "frenzy" that results in their death by drowning. The huge popularity of this Oscar-winning film is often blamed for promulgating the suicide myth. Yet its narrator clearly states that it is a story "both true and false", before explaining that the lemming legend is retold "when the population cycle mounts to another peak" - which is pretty much what scientists think.

In other words, the film-makers seem to have taken the rap for audiences who only heard what they wanted to hear - which is often the explanation why, as Mark Twain famously put it, "A lie will go around the world while truth is pulling its boots on". Except he didn't: the aphorism originates in a sermon by the 19th century English preacher Charles Spurgeon. But what about the many other bits of scientific dross that have been transformed into mythical gold? Why, for example, do so many people believe that water always spirals down plugholes anticlockwise in the northern hemisphere and clockwise in the south?

It could be because there is actually a grain of truth in it, in the form of the Coriolis Effect which tends to sweep everything along in the direction of the Earth's rotation. It's this force that causes giant weather systems like hurricanes to curl up into spirals as they move away from the Equator. On the tiny scale of a plughole, the Coriolis Effect is extremely weak, producing an acceleration ten million times weaker than gravity. Its influence is thus easily overwhelmed by, say, the tilt or shape of the wash basin. But if done very carefully, it is possible to detect the effect under laboratory conditions. In the 1960s, teams of researchers in the US and Australia carried out delicate experiments in which water was allowed to flow very gently out of very wide, shallow tanks. In both cases, the water spiralled out in the direction predicted by the Coriolis Effect.

Blunders by scientists left uncorrected for decades account for some urban myths. Take the supposedly amazing nutritional value of spinach. This myth was born in 1870, during research by a German nutritionist into the iron content of foods. While recording his result for spinach, he misplaced the decimal point - at a stroke, boosting the iron content of this boring leaf vegetable by a factor of ten. The myth really took off in 1929, when the American cartoonist Elzie Segar created the spinach-wolfing character Popeye. Kids everywhere were encouraged to eat heaps of the stuff, and spinach consumption soared by over 30 per cent between 1931 to 1936. Then nutritionists re-examined the iron content of spinach, and found it was no higher than for many other vegetables.

Not all such myths are so easily debunked, however. As all teenagers know, eating fatty foods and chocolate can trigger an attack of acne, yet doctors have long insisted that the true cause is hormonal, with surges in androgen leading to overproduction of grease by glands in the skin. But the truth is that no one is really sure about the role of diet in acne: studies which appear to give the all-clear to fatty foods and chocolate are far from conclusive, and a review of the evidence published in the medical journal Family Practice in 2005 found "surprisingly little evidence" either way.

There is a similar story with another myth: that scientists can't explain how a bumblebee flies. This one took wing in the 1930s, when a biologist at Gottingen University, Germany, asked an aerodynamics expert how fat, slow-moving bumblebees could flit so easily from flower to flower. After some calculations, the aerodynamicist had to admit that bee wings are just too small to generate lift like a conventional aircraft.

As bees don't fly like jumbo jets, that should surprise no one; even so, it was enough to give birth to the claim that scientists are clueless on the matter. Embarrassingly, it was not until 1996 that a team at Cambridge University found the source of the extra lift: vortices of low-pressure air attached to the bee's wings which act like tiny balloons. This appeared to nail the lie that scientists cannot explain something as "simple" as how bumblebees fly. But the story took an unexpected twist in 2001, when researchers at the University of California, Berkeley, pointed out that it was far from clear how the vortices remained attached to the bee's wings - without which they cannot provide extra lift

For the present, it seems scientists have no choice but to put up with the calumny that they cannot explain the flight of the bumblebee. And that highlights another oft-ignored fact about urban myths: the reason they are believed by so many people is because some of them are true. Robert Matthews is Visiting Reader in Science at Aston University, Birmingham, England