There was the time when a female, Aome, fell in love with a young researcher. She would literally cling to his leg when he moved around the island. Later another female, Imo, had the same attraction, and would sit on his shoulder. When this beloved researcher visited the island after an absence of six years, Imo remembered him and was particularly nasty toward his wife. Or, there was Utsubo, who, after her infant died, carried the corpse around until it began to decay. Such attachment is not unusual in mammalian mothers, except that Utsubo kept the desiccated body for no less than fifty-nine days! Then there was the occasion, in the postwar years, on which an American army commander wanted a pet monkey and asked villagers to hunt on the island. We also looked at pictures of twin monkeys born on the island, of a researcher who later drowned in a typhoon, of a visit by the American primatologist, Ray Carpenter, and of the slow deterioration of a female monkey with breast cancer.
Finally, there was the occasion, in September of 1953, on which Mito noticed how Imo, then an eighteen-month old juvenile, carried a sweet potato to a small freshwater stream that ran from the forest to the beach. Eating soiled potatoes wears down teeth, so it seemed a good idea to clean them. Imo did so by rubbing the potato in the water. She playfully repeated this behavior on the first day. Later, she improved her technique by going deeper into the water, holding the potato in one hand and rubbing off the mud with the other, occasionally dipping it in the water. No pictures remain of these events both because they happened unexpectedly and because their significance was fully realized only later on.
Mito didn't wait long to send a letter to distant Kyoto, where it was read by Imanishi and his students, including Kawamura and Masao Kawai. Very soon, Kawamura began collecting information resulting in a first Japanese article, in 1954.135 But perhaps the best-known article on the Koshima monkeys appeared ten years later, in 1965. Kawai put the exalted C-word in its title, even though he softened the blow with a prefix: "Newly Acquired Pre-cultural Behavior of the Natural Troop of Japanese Monkeys on Koshima Islet."
The discovery of potato washing is therefore best looked at as a team effort. Mito noticed it first; the cultural interpretation came from Imanishi; and Kawamura and Kawai collected the necessary information to convince the world of social transmission. Only a year before Imo's giant leap for monkeykind, Imanishi had speculated in writing about the possibility of animal culture, succinctly defining the phenomenon as "socially transmitted adjustable behavior." Thus, Mito's letter fell on fertile ground: her observations must have clicked in Kyoto. It was the first sign that the standard view that animal habits are handed down exclusively by genetic means needed revision.
Kawai's report is early Japanese priniatology at its best. It describes in admirable detail how potato washing first spread horizontally, from Imo to her playmates. Within three months, two of her peers as well as her mother were showing the same behavior. From these potato pioneers the habit spread to other juveniles, their older siblings, and their mothers. Within five years more than three quarters of the juveniles and young adults engaged in regular potato washing. Older males, however, failed to adopt the habit.116 Kawai explains that transmission seemed to follow the amount of time monkeys spent together, and that because males over the age of four typically live at the periphery of the troop, they had little exposure to potato washing.
Transmission according to kinship lines, and from the young to the young and the young to the old (rather than from the old to the young), also occurred after a second innovation by Imo. In 1956, she introduced a solution to the problem that wheat thrown onto the beach mingles with sand. Imo learned to separate the two by carrying handfuls of the mixture to nearby water, and throwing it into it. Sand sinks faster than wheat, making for easy picking. This sluicing technique, too, was eventually adopted by most monkeys on the island.
Acquired Taste
All monkeys present during my visit had been born long after these events. Even the oldest individual, an alpha male named Noso, was "merely" thirty-one years old. That Noso was still in power was truly remarkable given that he looked positively worn out. In captive monkey groups, I have known similar situations of an old male clinging to the top rank. Under those conditions, potential challengers are usually from the same group. Since they have known the old boss since infancy, it is logical to expect a psychological inhibition to attack him. In wild macaques, in contrast, challengers enter the troop from the outside, and hence are totally unhampered by such re spect. They make short work of an arthritic, feeble male like Noso.
But then, isn't Koshima a bit like a captive situation? All its monkeys spend their entire lives on the same island. In the annals of this place none of the alpha males has ever been overthrown: transfers of power have always taken place following the former alpha's natural death. 131
Noso and the others eagerly followed us around until they understood that we were not going to feed them right away. In exploring the island, I stepped over the little stream in which Imo had dipped her first potato and was introduced to her descendants. In the forest, I encountered some of the young males who didn't dare come down to the small stretch of beach where the main troop gathered and relaxed. I also climbed the island's 113-meter peak: high by the standards of a Dutchman, but surely laughable to Imanishi, a mountaineer who organized expeditions to the Himalayas.
Leaning over an outcrop, I looked down on fishermen standing on rocks in the ocean, some with a monkey waiting by their side. In the best sushi tradition of this country, the Koshima monkeys have learned to eat raw fish, mostly by taking discarded fish from anglers. This was first observed in a few hungry older males, after which the habit spread to other adults, including females, and then to the rest of the population. The path of transmission was totally different, therefore, from that followed with both of Imo's innovations.138 For all we know, these are the only Japanese monkeys to have acquired a taste for seafood. They also pry limpets from the rocks, and they have even been seen to capture octopi and fish trapped in small pools left behind during ebb.
Upon our return to the beach, the monkeys became quite excited. When the bags were finally opened, there was pandemonium and intense competition. While most of them chased each other around, quickly spreading the food to all corners of the beach, one male smartly sat down on a few potatoes while quietly nibbling on one. In the course of the hour or so that it took them to consume the food, I saw many monkeys run bipedally, both hands full, to the ocean. Walking in shallow water, they would alternate dipping a potato in it and chewing off a piece. They did not do much rubbing in the water, probably because these potatoes were prewashed: there was hardly any dirt to be removed. Soiled potatoes are not even commercially available anymore. For this reason, Japanese scientists have changed their terminology: they have stopped speaking of sweet-potato washing. Assuming that it is the salty taste of the water that the monkeys are after, they now speak of "seasoning."
Strange Rumors
In recent years, attention for these important discoveries has been diverted by two rumors. One sought to inject the events with a supernatural flavor, whereas the other derived from a skeptical reevaluation by a Western scientist.
In 1982, Ken Keyes published The Hundredth Monkey. Employing large lettering on almost empty pages and an abundance of exclamation marks, the booklet was designed to reach even the dimmest minds. Here are the contents of the critical four pages:
Let us suppose that when the sun rose one morning there were 99 monkeys on Koshima Island who had learned to wash their sweet potatoes. Let's further suppose that later that morning, the hundredth monkey learned to wash potatoes.
THEN IT HAPPENED!
By that evening almost everyone in the tribe was washing sweet potatoes before eating them. The added energy of this hundredth monkey somehow created an ideological breakthrough!
But notice. The most surprising thing observed by these scientists was that the habit of washing sweet potatoes then spontaneously jumped over the sea-Colon
ies of monkeys on other islands and the mainland troop of monkeys of Takasakiyama began washing their sweet potatoes!
Thus, when a certain critical number achieves awareness, this new awareness may be communicated from mind to mind.139
The insertion "observed by these scientists" implies that the birdlike migration of the habit was well-documented. Keyes' source, however, was not one of the Japanese primatologists, but a New Age author, Lyall Watson, who chose to interpret the occurrence of potato washing at distant sites as evidence that habits can spread through thin air. But all of this was coincidence; there is no indication whatsoever that what happened at Koshima affected events elsewhere.'40 Keyes, however, had a political, not a scientific, agenda. Opposing nuclear weapons, he exploited Watson's misconceptions to argue for group consciousness. If enough people join the nu clear freeze movement, so his reasoning went, their collective mind-set will break down political harriers. Readers of The Hundredth Monkey were urged to learn more by contacting an organization aptly named "ClearMind Trainings."141
One of the strangest ideas about the spread of potato washing is that the habit could have jumped from Koshima to other islands after a critical mass of one hundred monkeys had learned it. (Cartoon by Rob Pudim, published with permission of The Skeptical Inquirer, in which it first appeared, in 1985).
This leap-of-consciousness story is still doing the rounds in the American business community when motivational speakers want to impress audiences with the power of minds working together. Rumors tend to stay around, no matter how unsubstantiated. Since the same is true of criticism, I need to address here an influential scientific paper drenched in disbelief that monkeys might have culture. In 1990, Bennett Galef questioned whether the spreading of potato washing had anything to do with imitation.142 The Canadian psychologist was right to take a close look at the evidence and to insist that scientists carefully weigh the options when they see a behavior spreading in a population. The learning process may range from simple to quite complex, and it is important to gather data that permit making the right distinctions.
But given Galef's valid warning, it was all the more disturbing that he himself made so little effort to verify his own assumptions, for example, by actually visiting the island in person. Instead of social learning, he suggested individual learning-that is, that each monkey had acquired potato washing on its own without the help or example of others. One pillar of this claim was an aside hidden in the primate literature according to which potatoes were selectively handed out by Mito to those monkeys who washed them. Is it possible that she had stimulated the monkeys to do what the scientists wanted to see?
Galef's source was another researcher, an American, who did visit the island. However, this visit occurred no less than fifteen years after Imo had introduced potato washing.14 By that time, I was told, Mito would on occasion accommodate tourists and camera crews who wanted to document potato washing by feeding closer to the ocean and making sure that her best "performers" were at hand. All of this is irrelevant for the interpretation of how the habit started or spread: Kawai's analysis covered a much earlier period in which few outsiders ever showed up on Koshima.
But let us for a moment imagine that Mito did indeed reward potato-washing monkeys. How could this explain anything other than that monkeys who did it kept doing it? Reinforcement can strengthen an existing habit; it doesn't create one. Actually, withholding potatoes from those individuals who failed to wash them would be the best way to prevent potato washing from spreading. In other words, if Mito had done what Galef said she did, few monkeys would ever have had a chance to develop the habit.
But Mito didn't feed the monkeys in this manner. Her reaction to this suggestion, when I talked with her, was one of polite incredulity. Like anyone familiar with the strict hierarchy in a macaque society, Mito realizes that one cannot hand out food any way one wants. A large section of the group is low on the totem pole, and any monkey who possesses food at a time when the highest-ranking males have none is bound to get into deep trouble. Imo and her peers could therefore not have been favored too much at feeding time lest Mito put their lives in danger, which I am sure she did not want to do. To keep dominant males from making trouble, they needed to be fed first. And remember, adult males were the last ones to learn potato washing, if they learned it at all. 144
It became clear in my discussions with Mito that the feeding of potatoes started in the forest, away from the beach. Hence, the first potato washers had to actively seek out the water. Later, when the troop became better habituated and more attracted to the open area, provisioning nearer to the beach became part of the routine. It was again on their own initiative, however, that the monkeys switched their attention from the freshwater stream to salty water. In other words, the monkeys were in charge in all of this, not Mito.145
The second pillar of Galef's claim was that the speed with which the troop had adopted potato washing was far too slow for social transmission. He wrote: "One probable advantage of social learning over trial-and-error learning is that social learning is more rapid than trial-and-error learning. One sign of social learning should, therefore, be relatively rapid spread of a behavior through a population." 146 If social learning would be faster than individual learning, this would indeed be an advantage. But this is not the only advantage of social learning. As long as what is learned is a useful behavior that an individual would not have acquired by itself, the advantage is enormous regardless of speed. In addition, is it really that slow if a habit reaches half the population in five years, and the entire population under middle age in a decade? In the larger scheme of things, this is rapid change indeed, not unlike that induced by baby boomers in our own societies.147
The one point to concede to Galef is that it would be hasty to conclude that imitation was involved, if imitation means the intentional copying of someone else's actions. There is no evidence for this in the Koshima records, and the Japanese investigators themselves have wisely been neutral on the mechanism of transmission. It may have been as simple as stimulus enhancement, that is, one individual joins another who washes a potato, picks up pieces dropped by the other in the water, finds the taste attractive, and is thus primed to develop the same habit.
The strongest argument for social learning is the way the habit's trajectory through the group followed peer relations and kinship ties. It can hardly be coincidental that one of the first to follow Imo's example was her mother, who was seen washing potatoes within a few months of her daughter. The mother was clumsy at first, but gradually became more skillful, suggesting that even if she caught the "idea"-the association of potatoes with water-from her daughter, she still needed to refine the washing technique on her own.
This possibility doesn't strike me as farfetched, but after the monkeys had successfully spread their habit, people couldn't resist spreading rumors. In my field, there is vigorous debate about the validity of "anecdotal" information (based on single, unique observations), but at least most of the anecdotes that we consider are firsthand accounts by experienced animal watchers. In contrast, the overly enthusiastic story about monkey telepathy and the overly skeptical one about human influence are both armchair speculations.
Still Doing It
For over a quarter of a century now, the Koshima monkeys have received sweet potatoes only a couple of times per year. The food is unceremoniously dumped onto a dry section of the beach, after which there is a free-for-all. There is no selective reinforcement, no encouragement to approach the ocean, not even a need to clean the food. This is the situation most monkeys on the island have experienced all their lives. Yet, from the old to the very young, they are still doing what the late Imo began. Persistence of habits beyond the life of the initiator is one of the characteristics of culture.
Not only did Imo set things in motion on the island, she also got the juices flowing in the international scientific cornmunity. Is culture a uniquely human capacity, or are we justified in applying the concept to animals?
It would indeed have been baka-rashi for Imanishi and his students to have stayed with horses while such fascinating discoveries were waiting to be made nearby.
While we were preparing to leave, the island had grown unusually quiet. All of the monkeys had settled clown on the beautifully shaped rocks to groom, or just sit and nap. Apart from the occasional tantrums associated with weaningquickly resolved by a maternal embrace-the monkeys had taken on a dreamy attitude, no doubt due to the combination of a full stomach and a setting sun. Walking on the beach, I found the scene positively surrealistic. The eerie silence was reinforced by the fact that the monkey population here competes with birds over scarce foods, and the birds have lost. Apart from one diving osprey, and the ubiquitous kites high up in the air, there was not much that flew around. But for me the air was filled with history.
"We can approximate what culture is by saying it is that which the human species has and other social species lack."
Alfred Kroeber, 1923
"The ability to transmit learned behavior from generation to generation gave mammals an overwhelming advantage in the struggle for existence."
Ralph Linton, 1936148
he question whether animals have culture is a bit like whether chickens can fly. Compared to an albatross or falcon, perhaps not, but chickens do have wings, they do flap them, and they do get up in the trees. Imagine a world devoid of flying creatures except for the chicken: we would probably be mightily impressed, writing poems and songs about how we wished to be like them.
The Ape And The Sushi Master Reflections Of A Primatologist Page 16