Categorizing others into families may be a case of stimulus equivalence, as proposed by the late Ronald Schusterman, an American marine mammal specialist. Ron kept the strangest and most delightful animal laboratory that I have ever set a slippery foot in, since it consisted of not much more than an outdoor swimming pool in sunny Santa Cruz, California. It was the ultimate wet lab. To the side of the pool stood a few wooden panels on which symbols could be mounted for his sea lions. The animals swam in the pool, racing around faster than any human ever could, only to jump out for a few seconds and touch a symbol with their wet noses. Ron’s star performer was his favorite pinniped, named Rio. If Rio made the right choice, a fish would be thrown at her, and she’d dive right back into the pool. She did all this in one fluid movement, catching the fish while sliding back into the water, reflecting perfect coordination between experimenter and subject. Ron explained that most tests were too simple for Rio, resulting in her getting bored and losing her concentration. Making errors, she’d get mad at Ron for not giving her enough fish and angrily toss all her plastic toys out of the pool.
Rio had learned to associate arbitrary symbols. She’d first learn that symbol A belongs with B, then that B belongs with C, and so on. After rewarding her for making the right connections, Ron would surprise her with a brand-new combination, such as A and C. If A and B are equivalent as well as B and C, then A and C must be equivalent, too. Would Rio extrapolate from the previous associations, and group A, B, and C together? She did, applying this logic to combinations that she had never encountered before. Ron saw this as the prototype of how animals may mentally group individuals together, such as families or cliques.24 We do the same: if you learned to connect me first with one of my brothers, then also with another one (I have five!), you should also group those two brothers together in the same family even if you have never encountered them together. Equivalence learning makes for quick and efficient categorization.
Ron went further, speculating about other unseen connections. For example, chimpanzee males have been known to angrily attack and destroy the empty night nests that rival males have left behind in trees at the border of their territory. Unable to attack the enemy itself, the next best target is apparently a nest that they have built. It reminds me of a time in the Netherlands, when owners of black Suzuki Swifts had a tough time. They suffered frequent nasty remarks from people and worse, such as intentional damage to their cars. This situation arose after someone with murderous intentions had driven a black Suzuki Swift into a festive crowd on Queen’s Day, killing eight people. The car itself was obviously not at fault, but humans are quick to connect the dots. A hated action turned a specific car brand into a hated object. It all boiled down to stimulus equivalence.
Knowing as we do the spontaneous use of triadic awareness, the next question is how it is acquired. To find out, we need experiments. Is it enough for animals to just watch others? In one study, the French psychologist Dalila Bovet rewarded rhesus monkeys at Georgia State University for identifying the dominant monkey in a video. The observing monkeys didn’t know the individuals they were watching and had to judge their relationship purely on the basis of behavior. For example, one monkey in the video would chase another, after which the observer would be trained to select the dominant one (the one who had done the chasing) on a freeze frame of the scene. After learning to do this, the observing monkeys generalized to behaviors that didn’t look like chasing but also indicated dominance. Subordinate rhesus monkeys, for example, communicate their position to the dominant by baring their teeth in a wide grin. Bovet showed videos in which this signal was being exchanged. Even though these scenes were new to the observing monkeys, they correctly picked the dominant party. The conclusion was that they have a concept of rank and are quick to evaluate the status of unknown individuals on the basis of how they interact with others.25
Ravens may show a similar understanding, as evidenced by their reactions to vocalizations played over a loudspeaker. Ravens recognize one another’s voices and pay close attention to dominant and subordinate calls. But then the playbacks were manipulated to make it sound as if a dominant individual had turned submissive. Hearing evidence of a brewing overthrow, the ravens would stop what they were doing and listen while showing signs of distress. They were most upset by rank reversals among members of their own sex in their own group, but they reacted also to status reversals between ravens in an adjacent aviary. The investigators concluded that ravens have a concept of status that goes beyond their own position. They know how others typically interact and are alarmed by deviations from this pattern.26
In a related question, I have always wondered if captive chimpanzees evaluate status differences among the people around them. I once worked at a zoo with a demanding director who would occasionally visit the facilities and order everyone around, pointing out problems, saying this needed to be cleaned, and that needed to be moved, and so on. Showing typical alpha conduct, he kept everyone on their toes, as a good director should. Even though the chimps rarely interacted with him—he never fed them or talked to them—they picked up on this behavior. They treated this man with the utmost respect, greeting him with submissive grunts from a great distance (which they didn’t do for anyone else) as if they realized, Here comes the boss, the one everyone around here is nervous about.
It’s not just in relation to dominance that chimpanzees make such judgments. One of the best illustrations of their triadic awareness occurs in mediated conflict resolution. After a fight between male combatants, a third party may induce them to make peace. Interestingly, it’s only female chimps who do so, and only the highest-ranking ones among them. They step in when two male rivals fail to reconcile. The male rivals may be sitting near each other and avoiding eye contact, unable or unwilling to make the first move. If a third male were to approach, even to make peace, he’d be perceived as a party to the conflict. Male chimps form alliances all the time, so their presence is never neutral.
This is where the older females come in. The matriarch of the Arnhem colony, Mama, was the mediator par excellence: no male would ignore her or carelessly start a fight that might incur her wrath. She would approach one of the males and groom him for a while, then slowly walk toward his rival while being followed by the first. She would look around to check on the first and return to tug at his arm if he was reluctant. Then she’d sit down next to the second male, while both males would groom her, one on each side. Finally Mama would slip away from the scene, and the males would pant, splutter, and smack more loudly than before—sounds that signal grooming enthusiasm; but by then they would of course be grooming each other.
In other chimpanzee colonies, too, I have seen old females reduce male tensions. It is a risky affair (the males are obviously in a grumpy mood), which is why younger females, instead of trying to mediate themselves, encourage others to do so. They approach the top female while looking around at the males who are refusing to make up. This way, they try to get something going that they can’t accomplish safely by themselves. Such behavior demonstrates how much chimpanzees know about the social relationships of others, such as what has happened between the rival males, what has to be done to restore harmony, and who will be the best one to undertake this mission. It is the sort of knowledge that we take for granted in our own species, but without it animal social life could never have reached its known complexity.
Proof in the Pudding