However instructive all of these studies may be in showing how apes naturally develop group-typical signals and customs, it is especially from the field that we are receiving a steady stream of reports on cultural variants, many concerning tool use. Thus, chimpanzees at Bossou, in Guinea, have been seen to arrange leaves on the ground so as to avoid sitting directly on wet soil. It is unclear how long the Bossou chimpanzees have been using these so-called "leaf cushions."189 At a different site, in Sierra Leone, chimpanzees enter kapok trees to collect fruits, but these trees are full of sharp thorns that make it very painful for them to move around in the canopy. The apes have a unique solution that allows them to spend more time in these trees than apes at any other site. Breaking off small, smooth branches, they place these over the thorns and use them to step or sit on. Sometimes an ape holds a stepping stick between his greater and lesser toes, walking around with it "attached" to his foot. He thus has effectively provided himself with a protective sole, which the field-worker who first described it, Rosalind Alp, calls "foot-wear." This innovation shows that ape tools, like human hair bands and chairs, are sometimes invented as much for comfort as subsistence. 190
And then there is the mounting evidence for self-medication. Some of it is widespread in all sort of animals, such as the eating of clay, which contains absorbent components resembling Kaopectate, a commercial drug against diarrhea and stomach upsets. But apes are also known to chew the bitter pith of certain plants and to swallow whole leaves of others, both of which are assumed to have health benefits. Michael Huffman saw chimpanzees remove the outer bark and leaves of young shoots of Vemonia amygdalina to extract extremely bitter juice. Nearly all these chimpanzees showed diarrhea, listlessness, and worm infections. Fecal analysis revealed a striking drop in one chimpanzee's nematode infection following bitter pith chewing, a drop not seen in chimpanzees not taking this medicine. The same plants' bark and leaves contain toxins that can kill laboratory mice, but the chimpanzees must have learned to avoid these parts and extract only the beneficial compounds. For many African ethnic groups Vernonia is an essential ingredient in concoctions to treat malaria, dysentery, and a number of intestinal parasites.
Perhaps the best-known discovery, by Richard Wrangham and Nishida, is the ingestion of Aspilla leaves by chimpanzees at Gombe and Mahale. Before consumption, these hairy, rough-surfaced leaves are carefully folded with tongue and palate so that they can be swallowed whole. Since they are not chewed, they end up in the feces undigested. Chimpanzees tend to swallow them in the morning, before foraging for food. Huffman has shown that they act as a mechanical device to expel internal parasites. Since its initial discovery, leaf swallowing has been identified in a great many chimpanzee populations across Africa, involving over thirty different plant species. Regional differences in plant selection hint at cultural transmission.
It remains unclear how chimpanzees in the forest have learned bitter-pith chewing and leaf swallowing. Experimentation with novel foods, especially those that are inedible or taste bitter, is uncommon. Perhaps the medicinal properties of certain plants were discovered by accident during a period of food scarcity. Once established, offspring watched their mothers ingest these plants and noticed the unusual way of handling them. This may have predisposed the young to try things out for themselves. For the moment, however, all of this is pure conjecture. Since self-medication seems hard to acquire without the example of others and is assumed to assist survival, it remains high on the agenda of research into chimpanzee culture.191
How behavior is being transmitted remains a central puzzle in cultural primatology, one that can be solved only experimentally. Fieldwork, however, yields strong hints of what to look for. For one thing, observations of primates in naturalistic settings suggest that the usual laboratory approach, with human experimenters demonstrating actions to apes, is flawed. This procedure may occasionally work, but evolution is unlikely to have equipped animals with much of a tendency to mimic strangers of their own kind, let alone those of another species. As discussed in the previous chapter, the typical context is that of BIOL (bondingand identification-based observational learning), according to which mothers, peers, and other favorite social companions are most readily emulated. The desire to fit in sets the motivational stage, so to speak, for the actual learning process and provides its main incentive.
You Scratch My Back
The simplest kind of transmission is illustrated by the battle between milkmen and blue tits in Great Britain in the 1930s. At the time, milk was still delivered in glass bottles at the doorstep. The bottles were covered with a cardboard lid; directly underneath was the cream, which had risen to the top of the milk. Blue tits (related to chickadees) have a habit of peeling back bark to look for insect larvae; hence, removing a cardboard lid may have been a natural thing to do, and it would yield an immediate creamy reward. Once one bird had developed this habit, other birds would find bottles opened by this bird, taste the cream, and become eager to open bottles for themselves. Replacing the cardboard lid with aluminum foil caps didn't stop the birds, and the habit spread gradually from one city to all of the British isles.192
A blue tit (chickadee) eating cream after having removed the aluminum foil seal on a milk bottle. When milk in Great Britain was still being delivered at the door, this feeding technique spread like wildfire. After encountering previously opened bottles, naive birds may have been able to figure out the rest on their own. (Drawing by Margaret La Farge, with kind permission of the artist).
In my view, culture is a social phenomenon, however, which means that the example of others is required before I call a habit culturally learned. Milk-bottle opening by blue tits doesn't qualify, since it is unclear whether the birds actually needed to see other birds do it. They may have learned it as a result of environmental modification by other birds. I rate transmission in the absence of models quite differently than I rate, for example, the way the Koshima monkeys developed sweet potato washing. The fact that this habit spread first within families and among peers strongly suggests that the as sociation between potatoes and the ocean was learned in a social context, probably from being close to others who already showed the habit, watching them, and tasting discarded pieces. This satisfies my requirements for cultural learning.
To show that such examples are not limited to primates, another well-studied case is that of roof rats surviving in a pine forest. I always see the squirrels outside my window as rats with fluffy tails, but of course squirrels are perfectly adapted to an arboreal life in ways that rats are not. Rats don't belong in the trees, yet in one newly planted Israeli forest devoid of squirrels, rats have made a living out of extracting seeds from pine cones. A human trying to do the same with a pocket knife quickly notes that this is a strenuous task. In the laboratory, the same rat species was deprived of food and given cones for several weeks, but less than three percent of the adults learned by themselves how to open them. It is not a genetic characteristic either, because young rats from mothers that do strip cones will not learn it if they are foster-reared by females that don't. Most likely, the young learn the technique by being close to their mothers on foraging trips to the trees, perhaps feeding on the same cones next to her. Even if all they learn is that underneath the scales resides good food, the rest of the technique can be developed by themselves. Since they learn this in a social setting, it qualifies as a cultural tradition, and one with great survival value at that. Biologically, these rodents are rats, but culturally they are on their way to becoming squirrels.193
More complex forms of learning are those in which one individual copies the actions of another. Work on great apes, in particular, indicates that they pay attention not only to where but also how others obtain food. Duplication of another's methods, which has been demonstrated experimentally, is getting close to imitation.194 Carel van Schaik has proposed that a precondition for such learning is tolerance. Van Schaik discovered a group of orangutans in a Sumatran peat swamp, at Suaq Balimbing,
with an elaborate tool technology. Until then, the Asian red ape had never shown much of a proclivity for tool use in the wild even though its counterpart at the zoo is known as about the handiest tool manipulator of the animal world. As if to illustrate my earlier point that it is unusual for capacities seen in captivity not to be expressed also in the field, and vice versa, the Suaq Balimbing orangs poke twigs into holes to extract honey from stingless bee nests, and remove the seeds of Neesia fruits with short sticks that serve as both wedge and spoon. The seeds are embedded in stinging hairs and so cannot be removed by hand. The orangs modify their tools by breaking them, stripping off leaves, or chewing the end, thereby fraying them.
According to van Schaik, it is easier to concentrate on a tool task, and hence develop the most efficient technique, if one doesn't need to constantly look over one's shoulder for approaching competitors. The orangutans at Suaq Balimbing are remarkably gregarious and tolerant for their species, which further helps in the transmission of skills, as it means that oth ers can watch at close range what the more advanced tool users are doing. This may be the secret of their special tool culture; if low-ranking individuals don't dare to come close to a dominant at work, and need to avert their gaze so as not to draw attention to themselves, it will be hard to build up a cultural repertoire.195
For some behavior it is unclear how it could possibly be transmitted. During my time in Japan, I heard of two striking examples, both relating to the most ubiquitous social pastime of primates: grooming. Ichirou Tanaka is conducting perhaps the finest-grained animal behavior study I have ever seen, which focuses on the exact technique by which a Japanese monkey removes louse eggs from the hair of the ones that it grooms. Louse eggs are like tiny little doughnuts stuck around the base of a hair. They need to be loosened and taken between thumb and forefinger to be drawn to the hair tip before they can be transported to the mouth of the groomer and eaten. After taking close-up videos of more than four thousand sequences of louse-egg handling, Tanaka concluded from slow-motion analysis that some monkeys are very good at it (removing the egg in a single twisting-combing movement), whereas others are, well, lousy. One might think that the difference has to do with experience, but the investigator found no relation with the groomer's age. Instead, the level of proficiency depended on the family a monkey came from. Since Tanaka doesn't believe that this sort of detailed skill is genetically inherited, it must be learned. Do monkeys really pay such close attention to each other that they notice how their relatives treat each and every single hair when they groom? It is hard to imagine, but not impossible.196
The second example, first recognized as a custom by Linda Marchant, concerns the chimpanzees at the Mahale Mountains. One chimpanzee will walk up to another, vigorously scratch the other's back a couple of times with his or her fingernails, then settle down to groom the other. In between the grooming, more scratching may follow. It is an extremely simple behavior, one that cannot be hard to learn for an animal that commonly scratches itself. But here's the rub: usually one scratches oneself in reaction to itching, and enjoys immediate relief as a result. Scratching someone else is really something else, for the scratcher obtains no reward.
The second puzzle is this: why is this behavior limited to Mahale? Other chimpanzee communities have been studied for decades by astute observers, yet they don't back-scratch at all. In a recent analysis, Michio Nakamura proposes two ways in which the behavior may have spread at Mahale. One is imitation of the scratching movement by a bystander. Note that the recipient cannot see the action performed on his back; hence, it is more likely that a third chimpanzee sees another do it and then copies the movement. The problem with this explanation is that imitative learning usually assumes a reward for the imitator. In the case of the social scratch, however, all benefits go to the recipient, and the imitator gets nothing out of it.
The second possibility is even more intriguing. Imagine that one chimpanzee was accidentally scratched by another, and it felt so good that he decided to offer the same pleasant experience to another chimpanzee, perhaps one that he wanted to ingratiate himself with, such as the boss. This would require perspective-taking; that is, he would have to translate a bodily experience into an action that re-creates the same experience in another individual. He would need to understand that what he felt can also be felt by another. This is a highly complex capacity, related to empathy and role reversal, for which there are indeed indications in the spontaneous helping behavior and deception of apes.197
This brings me to the pinnacle of social transmission short of symbolic communication: active teaching. Teaching requires the same perspective-taking mentioned above, because one needs to gauge the knowledge of the other, and judge it deficient, before one can fill in the gaps through instruction. A good teacher enters a pupil's shoes. Evidence for such a process is minimal at this point, but Christophe Boesch has seen mother chimpanzees in Tai Forest facilitate the learning of nut cracking by leaving hammers, nuts, and anvils in a ready-for-action position for their infants to use. This seems intentional, because normally adults finish all of their nuts and take the hammer with them. Boesch reported how mothers sometimes perform the cracking motions, which are very rapid, in slow motion while paying attention to the gaze direction of their offspring, as if showing them how it is done. Mothers were also seen to "correct" an unsuccessful youngster by removing a nut that it was working on from the anvil, clean the anvil, and reposition the nut, or by reorienting the hammer that the offspring was holding. Since there are so few of these remarkable observations, they may not convince everyone, yet they at least hint at a serious possibility. 198
A jackdaw explains to a class of youngsters which enemies to watch out for. Active teaching, however, is extremely rare in nature. (Drawing by Konrad Lorenz, from Er redete mit dem Vieh, den Vogeln and den Fischen ~> 1983 Deutscher Taschenbuch Verlag, Munich. This book, which first appeared in 1949, was translated as King Solomon's Ring).
Perhaps the strongest evidence for teaching comes from an entirely different class of mammals. Christophe Guinet has observed killer whales, or orcas, teaching a complex hunting technique to their young. Orcas sometimes strand themselves intentionally, throwing themselves onto Argentinean beaches with breeding seals, grabbing one before they retreat to the ocean. This is a hazardous technique that, if performed incorrectly, may lead to permanent stranding and death for the predator. Adult orcas have been seen to encourage their young to strand on beaches devoid of seals. The adults push the young onto a beach, after which they help them out, in case they get stuck, by creating wash. They have also been seen to push young in the direction of prey on a beach, and if the young don't capture any, to throw their own prey at them. Since adult orcas seem to hunt better without young around, this means that they adjust their behavior in a way disadvantageous to themselves but beneficial to the young apprentices. All of this gives the impression of active instruction.
The gamut of cultural transmission in animals thus runs from picking up simple associations, such as between potatoes and water or between pine cones and seeds, to imitation of actual techniques, such as nut cracking, and perhaps even to perspective-taking and teaching of the young. It will take great effort by scientists in both the field and the laboratory to sort out which processes apply, but it is already clear that the conclusion that animal culture must rest on simple processes is premature.
Of Memes and Genes
When William McGrew published his landmark Chimpanzee Material Culture in 1992, a work that got the field of cultural primatology off to an excellent start, he didn't once mention "memes." Nor did Boesch and Michael Tomasello refer to memes when, in 1998, they held hands across the divide between field primatology and experimental psychology in a stimulating article in which they concluded that "in comparing chimpanzee and human cultures, we have noted many deep similarities." 199
Nevertheless, in the minds of some people, talk of cultural transmission means talk of memes. The term compares the way cult
ural information is being copied with how genes send copies of themselves down the generations: memes are packages of information that spread, or don't spread, similar to the way some genes fare better at replicating themselves than others.200 Having followed its own advice of heavy advertising, the meme concept has generated tons of references to itself. But even though the scientists just mentioned surely have heard of it, the concept is not in vogue among those who study cultural learning in animals. This is because parallels between genes and memes are about as useful as those between brains and computers. There was a time when the brain was explained as having software and hardware, as having memory banks and running programs. The urge to relate the new to the familiar-with the familiar serving as security blanket from which the new is explored-leads us sometimes into misleading comparisons. With the progress of neuroscience all of this has been forgotten; the brain is emphatically not a wet computer. Even when both handle the same task, such as playing chess, they achieve their ends in totally different ways.
Similarly, genetic evolution is a poor model for cultural change. In contrast to genetic instructions handed down from parents to children, culture is more like a set of suggestions broadcast to any recipient with an antenna to pick up the signal. New habits, such as dancing the Macarena or saying "ciao" for goodbye (except in Italy, where they have done so for a while), travel quickly in all possible directions and may reach an entire population without necessarily providing much of a fitness advantage. Most importantly, rather than coming about through random mutation, habits often result from deliberate choice: culture can be consciously created. Whereas an entire group of scientists keeps trying to shoehorn cultural transmission into the flawed metaphor of genetic evolution, students of animal behavior are wisely treating culture as a phenomenon with its own dynamics, most of which have barely been explored.
The Ape And The Sushi Master Reflections Of A Primatologist Page 20