Hundredth monkey effect

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The hundredth monkey effect is a hypothetical phenomenon in which a new behaviour or idea is said to spread rapidly by unexplained means from one group to all related groups once a critical number of members of one group exhibit the new behaviour or acknowledge the new idea.[1]

One of the primary factors in the promulgation of the story is that many authors quote secondary, tertiary or post-tertiary sources which have themselves misrepresented the original observations.[1]

Popularisation of the effect[edit]

A behavioural 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 behavioural 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 behavioural 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 behaviour 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 behaviour instantly spread across the water to monkeys on nearby islands.

This story was further popularised 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 neighbouring 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.

Original research[edit]

The original Koshima research was undertaken by a team of scientists as a secondary consequence of 1948 research on semiwild 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 behaviour. While studying the group the team would drop sweet potatoes and wheat on the beach and observe the troupe's behaviour. In 1954 a paper was published indicating the first observances of one monkey, Imo, washing her sweet potatoes in the water. Her changed behaviour led to several feeding behaviour 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 behaviour. A brief account of the behavioural changes can be seen below:

  1. The young first teach their contemporaries and immediate family, who all benefit from the new behaviour and teach it to their contemporaries
  2. If the parents or their contemporaries (or their parents) are too old, they do not adopt the behaviour
  3. Once the initial group have children, the dynamic changes from teaching previous and current generations, to the next generation learning by observation. The behaviour 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 behaviour 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 behaviour 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 behaviour started. To the contrary, it indicated that certain age groups in Koshima would not learn the behaviour.

Further research[edit]

Separate papers make mention that, from 1960 onward, similar sweet potato washing behaviours 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 behavioural improvements are made. No indication of how the monkey swam is made either - the Koshima monkeys cannot swim. Therefore, although the question must be asked how the swimming monkey learned the sweet potato washing behaviour if not from Koshima, no indication is made as to where the monkey learned the behaviour.

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 behaviour gradually spread through the monkey troupe and became part of the set of learned behaviours 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 favourite 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 popularised, 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]

See also[edit]


  1. ^ a b c d Amundson, Ron (Summer 1985). Kendrick Frazier (ed.). "The Hundredth Monkey Phenomenon". Skeptical Inquirer: 348–356.
  2. ^ Blair, Lawrence (1975). Rhythms of Vision: The Changing Patterns of Belief. London: Croom Helm Ltd. ISBN 978-0-8052-3610-1.
  3. ^ Blair, unlike Watson, does not assign the date 1952 to the observations.
  4. ^ Keyes, Ken (1984). The Hundredth Monkey. Camarillo: DeVorss & Co. ISBN 978-0-942024-01-2.
  5. ^ Whiten, Andrew; J. Goodall; W. C. McGrew; T. Nishida; V. Reynolds; Y. Sugiyama; C. E. G. Tutin; R. W. Wrangham; C. Boesch (1999). "Cultures in chimpanzees". Nature. 399 (6737): 682–685. doi:10.1038/21415. PMID 10385119.
  6. ^ Boesch, Christophe (2012). "31. Culture in primates. A - Culture as it Happens" (PDF). In Jaan Valsiner (ed.). The Oxford Handbook of Culture and Psychology. OUP. p. 678. ISBN 9780195396430. Retrieved 2014. Check date values in: |accessdate= (help)
  7. ^ Trivedi, Bijal P. (February 6, 2004). ""Hot Tub Monkeys" Offer Eye on Nonhuman "Culture"". National Geographic Channel October 28, 2010/National Geographic. Retrieved February 2014. Check date values in: |accessdate= (help)
  8. ^ a b Galef, B. G. (1992). "The question of animal culture". Human Nature. 3 (2): 157–178. doi:10.1007/BF02692251. PMID 24222403.

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