It's called "the hundredth monkey phenomenon" and in recent years word of it has spread widely, leading many people to believe that scientists have discovered a genuine, new kind of paranormal event.

What happened, so the story goes, was that whole troops of monkeys living on widely separated Japanese islands spontaneously acquired a new behavior -- washing sand off food by dunking it in water -- after a critical number of animals on one island learned the practice by the conventional method of imitation.

The idea is that once a certain number of minds, 100 monkey minds in the most famous example, share a common idea, they activate something called a collective consciousness that immediately transmits the same idea to other minds.

The putative phenomenon was first popularized in a 1979 book, "Lifetide" by Lyall Watson, and since then has gained increasing currency in other books, magazines and films. Elements of the nuclear disarmament movement have promoted the idea with the assertion that if enough human minds can be won to their cause, the whole world will suddenly be seized by an urge to disarm.

The truth, according to a University of Hawaii professor who examined the evidence, is that "there is no hundredth monkey phenomenon," that the notion of a spontaneous spread of a behavior among Japanese monkeys is a fiction that is completely refuted by the published data of the same Japanese primatologists who, it is claimed, discovered the phenomenon.

The debunker is Ron Amundson, a philosophy professor who specializes in the philosophy of science and the rise of pseudosciences. His report appears in the current issue of The Skeptical Inquirer, the quarterly journal of the Committee for the Scientific Investigation of Claims of the Paranormal. The committee was formed about 10 years ago by a group of scientists and others hoping to counteract what they saw as a rising tide of belief in supernatural phenomena.

The hundredth monkey phenomenon traces its origin to research in the 1950s by Japanese scientists who were studying free-roaming troops of macaques that live on a few small islands. In 1952 the scientists began giving the monkeys on Koshima Island sweet potatoes as food, tossing the tubers onto the beach. The following year the scientists observed that one young monkey, named Imo, discovered she could wash sand off the potato by dipping it in the water. And perhaps the potato tasted better salted, as well, so she kept up the behavior.

Over the ensuing years, as scientists watched closely, other monkeys copied the practice. As the young macaques grew up, they taught it to their offspring.

In 1958, according to the challenged book by Watson, an astonishing thing happened.

"One has to gather the . . . story from personal anecdotes and bits of folklore among primate researchers," Watson wrote, "because most of them are still not quite sure what happened. And those who do suspect the truth are reluctant to publish it for fear of ridicule.

"In the autumn of 1958 ," Watson went on, "an unspecified number of monkeys on Koshima were washing sweet potatoes in the sea . . . . Let us say, for argument's sake, that the number was 99 and that at 11 o'clock on a Tuesday morning, one further convert was added to the fold in the usual way. But the addition of the hundredth monkey apparently carried the number across some sort of threshold . . . . because by that evening almost everyone was doing it. Not only that but the habit seems to have jumped natural barriers and to have appeared spontaneously . . . in colonies in other islands and on the mainland."

Amundson, in attempting to verify Watson's version of events, checked the published reports of the Japanese scientists, who kept daily track of every monkey on the islands and recorded their behaviors in great detail. He found there was no sudden jump in the number of spud-dunking monkeys. From Imo, who invented the practice, it spread gradually, a little faster in early years and more slowly later.

In 1958, the year Watson claimed the sudden jump appeared, the Japanese researchers marked a different transition. That was when the behavior stopped spreading among young, imitative monkeys. The only form of transmission after 1958 was from parent to offspring. The reason was that all the young monkeys had grown to become the parental generation.

Masao Kawai, the primatologist who published the most comprehensive reports, did find that potato washing appeared on other islands but left no mystery about how it happened. In one case a potato-washing monkey swam to a nearby island in 1960 and stayed there for four years. His arrival marked the introduction of the practice there. On other islands, it started spontaneously, with a single monkey, as on Koshima, but never spread as completely.

Watson could not be reached for comment. His publisher, Simon and Schuster, declined to give out his telephone number or address.

Michael Korda, who edited the book, said Watson "is a distinguished and eminent scholar who, I have to say, does have some weird ideas."