Of Sweet Potatoes, Social Cognition, and Spiritual Hullabaloo

I did my Ph.D. using monkeys as a model system, and as such I have quite an affinity for the little buggers. They may not be cute, they may not smell good, and they're definitely not cuddly, but they're completely endearing due to their penchant for outsmarting their H. sapiens bretheren. Unfortunately, not even an irascible, crusty old primate is immune from pseudoscientific nonsense. The Hundredth Monkey is one example.

The Hundredth Monkey Phenomenon is often referred to by pop psych weirdos and New Age crazies. If you hang around any internet forums, eventually some incense-burning quasi-spiritual nutjob will bring it up. Basically, the story goes like this:

The Japanese monkey, Macaca fuscata, had been observed in the wild for a period of over 30 years. In 1952, on the Island of Koshima, scientists were providing monkeys with sweet potatoes dropped in the sand. The monkeys liked the taste of the raw sweet potatoes, but found the dirt unpleasant. An 18 month old female named Imo found she could solve the problem by washing the potatoes in the salty ocean water, improving the taste of the potato. She taught this trick to her mother. Her playmates learned this trick and taught their mothers too. This cultural innovation was gradually picked up by numerous monkeys in the troop and observed by the scientists.

Between 1952 and 1958, all the young monkeys learned to wash the sandy sweet potatoes and make them more palatable. Only the adults who imitated their children learned this cultural improvement. Other adult monkeys kept eating the dirty sweet potatoes. In autumn of 1958, something startling took place. A certain number of Koshima monkeys were already washing their sweet potatoes, the exact number is not known. The hypothetical number given was 99. Then it happened. The hundredth monkey learned to wash the sweet potatoes. The added energy of that hundredth monkey somehow created an ideological breakthrough. Almost everyone in the tribe was washing their potatoes before eating them, but a surprising occurrence was observed by these scientists. The habit of washing the sweet potato had jumped overseas. Colonies of monkeys on other islands and the mainland troop at Takaskiyama began washing their sweet potatoes.

Although the exact number may vary, this Hundredth Monkey Phenomenon means that when only a limited number of individuals knows a 'new way', it remains the conscious property of those individuals. However, when one more individual manifests this new awareness, the field is strengthened, a critical mass is reached, and the awareness becomes the conscious property of all. This new awareness is communicated mind to mind.

From The Hundredth Monkey by Ken Keyes Jr.

Now this story has been eviscerated elsewhere (some nice links exist on the Wikipedia article), but I'm going to give a somewhat original take on it- I'm going to assume, for the sake of argument, that the story happened roughly as told (it didn't), but argue that it neither necessitates nor even supports an outlandish paranormal bastardization of Jungian psychology to explain the behavior miraculously jumping to other macaque populations.

Monkeys are a lot like people. Specifically their young are much more adept at picking up new skills, and it is no surprise that once one monkey figured out how to wash potatoes, the other young monkeys of the troop were more likely to begin washing sweet potatoes than were other older monkeys. So how would the behavior magically get off the island? Quite simple, actually; swimming.

After a male monkey hits puberty, it is not uncommon for it to migrate to a new troop. This is, of course, evolutionarily advantageous, as the monkey then gets to introduce its genes to a new group of females, engage in harem-building, and reduce intrasexual mating competition. So male monkeys leave the island by swimming to the mainland or other islands (the islands are actually located within swimming distance to the mainland). Before you think I'm insane for suggesting that monkeys would wilfully hop in the ocean, I would like to point out that my boss has actually visited these islands and confirmed with the researchers there that yes, they do swim between islands and the mainland.

Interestingly enough, the timing of the story coincides with the beginning of the breeding season-- monkeys typically begin their breeding season at the end of autumn, so migrating in autumn would be a good idea (and is actually what happens). Next thing you know, the young of the new troop are imitating the washing behavior, in the autumn, as the story suggests. Even more interesting, Japanese macaques (Macaca fuscata) usually don't disperse from their natal group until after five years; note that even if one adheres to the story, monkeys began washing sweet potatoes in 1952 and the behavior appeared in other troops in 1958..... 6 years later.

So there you have it; even if one accepts the actual events of the story at face value, there is no reason to resort to paranormal explanations for a very natural phenomenon. So the next time somebody desires to perpetuate pseudoscientific malarky, tell them to leave the monkeys alone!!!