21 May, 2005 at 10:02 Leave a comment

Why don’t we just kiss and make up?

  • 07 May 2005
  • From New Scientist Print Edition. Subscribe and get 4 free issues.
  • Lee Dugatkin
  • Lee Dugatkin is a behavioural ecologist at the University of Louisville, Kentucky. His latest book Principles of Animal Behavior is published by W. W. Norton (2004)

LOOK at the world’s worst trouble spots and you can’t fail to notice they have one thing in common: tit-for-tat attacks between warring parties. Escalation of violence is incredibly destructive, yet we humans find it very difficult to break the vicious cycle. It seems we are not good at conflict resolution. Perhaps we could learn a lesson or two from the spotted hyena.

Spotted hyenas are highly sociable. Like other animals that live in close-knit groups, they don’t always get along. But spotted hyenas don’t hold a grudge. Within about 5 minutes of a fight, the erstwhile combatants can often be seen playing, licking or rubbing one another, or engaging in other friendly acts to dissipate the tension. And they are not the only animals with a penchant for kissing and making up. In their book Natural Conflict Resolution, Filippo Aureli from Liverpool John Moores University, UK, and Frans de Waal from the Yerkes Primate Center at Emory University, Atlanta, Georgia, document reconciliation in no less than 27 species of primates. Bottlenose dolphins also do it. Even goats. So why can’t we be more forgiving?

Admittedly, human interactions are far more complex. But perhaps we can draw some lessons from the study of conflict resolution in nature. Not only have ethologists discovered that it is a lot more common than you might expect, they are also working out the costs and benefits of conflict resolution. Their ideas about when, where and how reconciliation works in nature could help us to improve the chances of settling our own disputes.

When it comes to making up, our primate cousins get top marks. De Waal describes a typical incident in which Hennie, a young female chimp, has been slapped during a passing charge by Nikkie, the leader of the group. Hennie retires from the fray, at first caressing the spot where she was hit and then just lying in the grass and staring into the distance. “More than 15 minutes later Hennie slowly gets up and walks straight to a group that includes Nikkie,” de Waal writes. “Hennie approaches Nikkie, greeting him with a series of soft pant grunts. Then she stretches out her arm to offer Nikkie the back of her hand for a kiss. Nikkie’s hand kiss consists of taking Hennie’s whole hand rather unceremoniously into his mouth. This contact is followed by a mouth-to-mouth kiss.”

Note, it is Hennie, the chimp who came off worst in the argument, who instigates the reconciliation. In fact, this is a general pattern for most instances of conflict resolution. Gabriele Schino from the National Research Council in Rome, Italy, even found it in goats. After she had induced conflict over food, she found that 16 per cent of all interactions between goats were reconciliatory, consisting of friendly acts such as grooming and muzzle rubbing between animals that had been fighting previously. As in primates, this was most often initiated by the loser of the fight.

Like hyenas and most primates, goats are sociable animals. And this seems to be one of the key attributes of species that go out of their way to resolve their conflicts. Hardly surprising then, that such behaviour is also found in dolphins. Although they seem to have happy grins perpetually plastered on their faces, dolphins are surprisingly aggressive. And, sure enough, they are big on conflict resolution, as Amy Samuels from Woods Hole Oceanographic Institute, Massachusetts, and Cindy Flaherty from Brookfield Zoo in Chicago, Illinois, have observed. While studying a small group of bottlenose dolphins at the zoo, Samuels and Flaherty noticed that after a fight opponents often engaged in “gentle rubbing” or “contact swims”, in which one dolphin towed another through the water.


Documenting such interactions has made ethologists aware of just how common conflict resolution is in nature and they are developing theories about how conflict-resolving behaviour evolves. Their cost-benefit models attempt to make specific predictions about when and where potential combatants will devise non-aggressive ways to resolve disputes, and under what circumstances they will adopt special conciliatory behaviour to minimise the chances of further conflict after an altercation. These models are now being put to the test.

The benefits of being in a social group often depend on its stability. That means conflict resolution is likely to figure large in groups where aggression will really rock the boat – if the size of a group is important for its successful functioning, for example. If subordinate individuals were to defect every time they lost a fight, the group would be in a constant state of flux, with potentially disastrous results, in terms of less food, fewer individuals available to fight competing groups, and so on. Even if subordinates stayed put, without reconciliation they would probably have limited access to resources. Those who try to resolve conflicts can avoid this fate. That gives them an advantage over others who do not engage in this behaviour, and explains how it might have evolved.

But it takes two to kiss and make up. Why would the winner of a fight play ball? Because dominant individuals also have something to gain from reconciliation, it turns out. Without resolution, they can never be sure a fight won’t flare up again. And that can lead to anxiety and raised levels of stress hormones called corticosteroids. These in turn compromise the immune system making individuals more likely to succumb to infection. Evidence of reconciliation’s value as a stress-buster comes from physiological measurements taken before and after it occurs, showing that making up leads to a decreased heart rate.

Given these biological and psychological costs, it is not surprising that natural conflict resolution is rife in tightly knit social groups. In fact, reconciliation is so beneficial to a group of chimps that if neither of the warring individuals will initiate it, a third party may step in to broker a deal. Nevertheless, not all cases of aggression are equally likely to involve resolution, because the costs and benefits of reconciliation vary depending upon what caused the incident in the first place. Researchers have found, for example, that in primates at least, reconciliation almost never happens when individuals fight over food, whereas it is common following aggression that appears to have no specific motive. In general, fights over a finite resource tend to have a natural lifetime that ends when the resource is used up. Resolution is unnecessary because such fights are unlikely to affect long-term bonding between group members. Fights that are more nebulous in origin, by contrast, have the potential to flare up again unless there is closure.

Feuding families

In addition, some pairs of combatants are more likely to seek reconciliation after a fight than others. One of the most influential models of natural conflict resolution is the valuable friendship model, suggested by de Waal and Aureli, which is built on the idea that the more you depend on another individual, the more costly it is to allow a rift to develop. Detailed controlled experiments testing the hypothesis are rare, but one study with long-tailed macaques found that reconciliation is indeed more likely after fights between partners who normally help each other get food than between other individuals. What’s more, for a wide range of primates the most valuable social relationships tend to be among kin, and disputes within families often end in reconciliation. This is not the case with spotted hyenas, however. Kay Holecamp from Michigan State University and her team have found that hyenas are more likely to initiate reconciliation with non-kin than with kin. Not, they suggest, because family relationships are less valuable, but because kin may be more forgiving of one another than strangers are.

These are the benefits of reconciliation, but what of the costs? There must be some or you would expect to find conflict-resolving behaviours in all animals that live in groups and in all contexts. One possibility is that reconciliation requires a level of cognitive complexity beyond the reach of many species. The evidence, however, does not support this. Behaviours that are cognitively sophisticated tend to involve learning. But young animals are just as competent at reconciliation as adults. So if cognitive constraints do not seem to be the problem, what is?

An obvious answer is that when former aggressors come together to try to make up, fighting may re-ignite. One way around this problem is to adopt special reconciliation rituals that are hard to misinterpret. Indeed comparative studies reveal that in species where reconciliation is most common it is more likely to be associated with unique, unambiguous actions such as “embracing” in pig-tailed macaques and “grasping” in Tonkean macaques. But even this cannot get around the fact that the benefits of reconciliation may outweigh the costs for only one member of a warring pair. Finally, reconciliation may be unnecessary in certain societies. Ring-tailed lemurs, for example, are either friends, almost always interacting peacefully and to mutual benefit, or enemies who never get along. Between friends, reconciliation is unnecessary. Between enemies it is simply a waste of time.

As our understanding of natural conflict resolution grows, it is tempting to hope that we can apply what we have learned to improve human relations. The cost-benefit approach certainly looks like a step in the right direction, but we will need much more detailed work on non-humans before we can develop general predictions that might apply to us. The possibilities are tantalising, though.

Take the study of rhesus and stumptail monkeys done by de Waal and colleague Denise Johanowicz over a decade ago. Rhesus monkeys are aggressive and rarely opt for reconciliation; stumptails on the other hand have a talent for making up. The researchers wanted to see what would happen if they reared juveniles of the two species together. They found that the young stumptails exerted a benign influence over the slightly younger rhesus monkeys, whose behaviour towards other group members gradually became more and more conciliatory. The idea that natural conflict resolution can be taught by observation means that there is some hope for Homo sapiens.

The different reconciliation styles of chimpanzees and bonobos could also offer a pointer to human behaviour. Bonobo society is particularly harmonious, and one way they achieve this is through reconciliation. This is a notoriously sexy affair, often involving “mounts” and other erotic activities. In contrast, sex is far less important in chimp conflict resolution. But, according to de Waal, what really makes the difference is not the sexual element but who instigates reconciliation. Chimps follow the usual pattern, with the loser trying to make amends. For bonobos, however, it is the winner, the individual wielding the power, who makes the first move. Now there is a lesson for us all.


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