Hundredth monkey effect

A behavioral study was conducted in the 1950s of a troupe of Macaca fuscata (Japanese monkeys) on Kōjima island. An unanticipated byproduct of the study was that the scientists witnessed several evolutionary behavioral changes by the troupe, two of which were orchestrated by one young female, and the others by her sibling or contemporaries.

The account of only one of these behavioral changes (sweet potato washing) was propagated into a phenomenon and the story loosely published by Lawrence Blair and Lyall Watson in the mid-to-late 1970s.[1]

The story of the hundredth monkey effect was published in Lyall Watson's foreword to Lawrence Blair's Rhythms of Vision in 1975,[2] and spread with the appearance of Watson's 1979 book Lifetide: The Biology of the Unconscious. The account is that unidentified scientists were conducting a study of macaque monkeys on the island of Kōjima in 1952.[3] These scientists observed that some of these monkeys learned to wash sweet potatoes, and gradually this new behavior spread through the younger generation of monkeys—in the usual fashion, through observation and repetition. Watson then concluded that the researchers observed that once a critical number of monkeys was reached, i.e., the hundredth monkey, this previously learned behavior instantly spread across the water to monkeys on nearby islands.

This story was further popularized by Ken Keyes Jr. with the publication of his book The Hundredth Monkey. Keyes's book was about the devastating effects of nuclear war on the planet. Keyes presented the hundredth monkey effect story as an inspirational parable, applying it to human society and the effecting of positive change.[4] Unfortunately, Keyes combined two items of truth: that the Koshima monkeys learned to wash sweet potatoes, and that the phenomenon was observed on neighboring islands. He did not provide substantiating evidence for his claims, diluting the importance of both studies and potentially discrediting the scientists involved. Combining this science with his political views may also have damaged the research credibility, leading to many reporters attempting to 'debunk' the Japanese team's research without doing sufficient research themselves.

The original Koshima research was undertaken by a team of scientists as a secondary consequence of 1948 research on semi-wild monkeys in Japan. The Koshima troupe was identified as segregated from other monkeys and, from 1950, used as a closed study group to observe wild Japanese monkey behavior. While studying the group the team would drop sweet potatoes and wheat on the beach and observe the troupe's behavior. In 1954 a paper was published indicating the first observances of one monkey, Imo, washing her sweet potatoes in the water. Her changed behavior led to several feeding behavior changes over the course of the next few years, all of which was of great benefit in understanding the process of teaching and learning in animal behavior. A brief account of the behavioral changes can be seen below:

1. The young first teach their contemporaries and immediate family, who all benefit from the new behavior and teach it to their contemporaries.
2. If the parents or their contemporaries (or their parents) are too old, they do not adopt the behavior.
3. Once the initial group have children, a change occurs in the dynamic of the behavior from teaching previous and current generations, to a new dynamic where the next generation learns by observation. The behavior is no longer actively taught but passively observed and mimicked.
4. The first innovator continues to innovate. The young monkey who started potato washing also learned how to sift wheat grains out of the sand by throwing handfuls of sand and wheat into the water, then catching the wheat that floated to the top. This invention was also copied using the above teaching and learning process until there were too many monkeys on the island with too little wheat apportioned, which is when competition became too fierce and the stronger monkeys would steal the collected wheat from the weaker ones, so they stopped the learned behavior in self-preservation.
5. The innovator’s sibling started another innovation whereas the monkeys were initially fearful of the ocean, only deigning to put their hands and feet into it, the wheat straining innovation led to monkeys submerging more of their bodies in the water, or play-splashing in the ocean. This behavior was again copied using the above teaching and learning processes.

The study does not indicate a catalyst ratio at which all the Koshima monkeys started washing sweet potatoes, or a correlation to other monkey studies where similar behavior started. To the contrary, it indicated that certain age groups in Koshima would not learn the behavior.

Separate papers make mention that, from 1960 onward, similar sweet potato washing behaviors were noticed in other parts of the world, however this is not directly attributed to Koshima. Claims are made that a monkey swam from one island to another where he taught the resident monkeys how to wash sweet potatoes. No mention of the other behavioral improvements are made and no indication of how the monkey swam – the Koshima monkeys cannot swim. Therefore, although the question must be asked how the swimming monkey learned the sweet potato washing behavior if not from Koshima, no indication is made as to where the monkey learned the behavior.

In 1985, Elaine Myers re-examined the original published research in "The Hundredth Monkey Revisited" in the journal In Context. In her review she found that the original research reports by the Japan Monkey Centre in Vol. 2, 5, and 6 of the journal Primates are insufficient to support Watson's story. In short, she is suspicious of the existence of a hundredth monkey phenomenon; the published articles describe how the sweet potato washing behavior gradually spread through the monkey troupe and became part of the set of learned behaviors of young monkeys, but Myers does not agree that it serves as evidence for the existence of a critical number at which the idea suddenly spread to other islands.

The story as told by Watson and Keyes is popular among New Age authors and personal growth gurus and has become an urban legend and part of New Age mythology. Also, Rupert Sheldrake has cited that a phenomenon like the hundredth monkey effect would be evidence of morphic fields bringing about non-local effects in consciousness and learning. As a result, the story has also become a favorite target of the Committee for the Scientific Investigation of Claims of the Paranormal, and was used as the title essay in The Hundredth Monkey and Other Paradigms of the Paranormal, published by the Committee in 1990.

In his 1997 book Why People Believe Weird Things, Michael Shermer explains how the urban legend started, was popularized, and has been discredited.

The original research continues to prove useful in the study of cultural transmission in animals.[5][6][7]

An analysis of the appropriate literature by Ron Amundson, published by The Skeptics Society, revealed several key points that demystified the supposed effect.

Unsubstantiated claims that there was a sudden and remarkable increase in the proportion of washers in the first population were exaggerations of a much slower, more mundane effect. Rather than all monkeys mysteriously learning the skill it was noted that it was predominantly a learned skill, which is widespread in the animal kingdom;[8] older monkeys who did not know how to wash tended not to learn. As the older monkeys died and younger monkeys were born the proportion of washers naturally increased. The time span between observations by the Japanese scientists was on the order of years so the increase in the proportion was not observed to be sudden.

Claims that the practice spread suddenly to other isolated populations of monkeys may be called into question given the fact that the monkeys had the researchers in common. Amundson also notes that the sweet potato was not available to the monkeys prior to human intervention. The number of monkeys in the colony was counted as 59 in 1962 indicating that even in numbers no "hundredth monkey" existed.[1][8]

• Confirmation bias
• Decline effect
• Meme
• Multiple discovery
• Tipping point (sociology)

• Carroll, Robert Todd (2005). "The Hundredth Monkey Phenomenon". Skeptic's Dictionary.
• Myers, Elaine (Spring 1985). "The Hundredth Monkey Revisited". In Context. Archived from the original on 2012-02-06. Retrieved 2004-09-01.
• Pössel, Markus; Amundson, Ron (May–June 1996). "Senior Researcher Comments on the Hundredth Monkey Phenomenon in Japan". Skeptical Inquirer. Archived from the original on 2004-08-03.
• Amundson, Ron (Summer 1985). Kendrick Frazier (ed.). The Hundredth Monkey Phenomenon. Skeptical Inquirer. Prometheus Books. pp. 348–356. ISBN 978-0-87975-655-0. Reprinted in The Hundredth Monkey—And Other Paradigms of the Paranormal (1991) (see online version under External links)
• Amundson, Ron (Spring 1987). Kendrick Frazier (ed.). Watson and the Hundredth Monkey Phenomenon. Skeptical Inquirer. Prometheus Books. pp. 303–304. ISBN 978-0-87975-655-0. Reprinted in The Hundredth Monkey—And Other Paradigms of the Paranormal (1991)

• "The Hundredth Monkey Phenomenon", Ron Amundson's copy of his Skeptical Inquirer article of 1985