Sunday, 27 October 2013
So many animals avoid fighting by simply avoiding each other. They mark out territories to warn off others of their species, to say 'this bit of land is mine, and you'll keep out if you know what's good for you.' When they do face each other, one of them - usually the interloper - generally backs down before things get violent. This is fine for animals that live on their own, but it's not so great when, as with many monkeys, the animal lives in a group, where you just can't stay out of each others' way.
The group may still mark out its territory somehow, and fight off outsiders when they need to. But there is still always going to be conflict within the group, especially where the society is clearly hierarchical, and one top monkey monopolises the mates, or just gets first pick of the food. Yet, while this conflict is necessary to establish the hierarchy in the first place, and gives benefits to those who come out on top, it's not good for the group as a whole.
A band of monkeys that constantly fights amongst itself is going to break up, and rather defeats the point of living together in the first place. So monkeys, as with other group-living animals, have developed strategies to deal with this, many of them based around, for example, mutual grooming.
Golden snub-nosed monkeys (Rhinopithecus roxellana), for instance, have recently become the latest in a number of species where females are known to groom males in exchange for sex. Later on in the year, however, females without babies engage in more grooming with successful mothers, apparently in return for the opportunity to touch their babies (a pleasurable thing to them, perhaps because it makes them feel like a mother, too).
But, in a cohesive social group with a clear dominance system, there is another option: dominant individuals can step in and break up fights. When this is done without showing any favour to either side in the conflict, it is sometimes called "policing". In the medium to long term, this helps cement the formation of larger, more diverse groups, with obvious benefits in terms of helping to mutually protect the group's young, look out for predators, and so on.
This has been observed in a number of species, including macaques and chimpanzees, although it is pretty rare. It isn't necessarily violent, either; it's perfectly possible to break up a fight by calming one individual down (by attempting to groom them, say), or just by walking over and looking tough in the hope that somebody backs off before you actually have to punch or bite them.
It is usually argued that, to count as policing, the intervention has to be impartial. If you're helping one monkey out against the other, it's probably because you want something in return. That makes it a selfish behaviour, with some clear-cut benefit to you that's worth the risk of you getting hurt breaking up the fight. True, you'll also benefit if the only thing that happens is that the group as a whole is stronger as a result of your actions, but since everyone else gains from that, too, it's something we can more accurately describe as 'altruism'.
Mind you, it might not be as entirely altruistic as it looks. For instance, by breaking up fights, you might be demonstrating to everyone that, yes, you are boss monkey, and they'd better not forget it. But if you weigh in one side or the other, it's much more likely that you're angling for something. But what?
There have been at least three possibilities proposed. Firstly, you might be helping out your friend (as in, somebody who grooms you a lot), in expectation of his or her assistance in the future. Secondly, you might choose to fight against individuals that are very close to you in the social hierarchy, thus proving to everyone that you're tougher than they are. Thirdly, if you have a tendency to help out members of the opposite sex, then it's fairly obvious what sort of favour you expect from them in return. You are, after all, a monkey, and haven't heard of gallantry.
We should be able to figure out which is the most important by seeing who monkeys do tend to support when they weigh into such fights. And, in the third case, by whether they get their expected reward from the grateful combatant or not. The answers are likely to vary from species to species, and won't always be clear-cut, but one recent study has chosen to look specifically at rhesus macaques (Macaca mulatta).
Rhesus macaques live in groups of anything up to 200 individuals, dominated by a small core group of older males and their partners. As is often the case, the sexes maintain separate hierarchies, with lower ranking males dominating smaller sub-groups within the overall troop. The researchers, Brianne Beisner and Brenda McCowan, watched the behaviour of a number of rhesus monkey groups at the California National Primate Research Centre, to see which, if any, of the explanations fit best.
The answer: pretty much none of them. There's no tendency, for instance, for monkeys to try and break up fights by attacking individuals similar in rank to themselves. This may be because the troops are based around a group of co-equal dominant males, and they're quite happy with that state of affairs. There's no need to fight your fellow oligarchs if you're already as close to the top as you're ever going to be. Nor is there any tendency for them to support their grooming partners over anyone else.
There was, perhaps, an increased likelihood of sexual favours from those that were helped out, but this wasn't always the case, not least because interventions frequently occurred outside the mating season. For that matter, monkeys often intervened in same-sex conflicts, where that wouldn't be an issue. So it may play a part, but the study seemed to show it was a fairly small one. When it did occur, it was mainly to the benefit of low-ranking individuals - the dominant monkeys presumably got to mate with whoever they wanted anyway, and didn't need to prove themselves in that way.
So what was their motivation? Well, breaking up fights, even when the intervening monkey was clearly biased in favour of one combatant, did have one noticeable effect. Groups where this happened more frequently had less fights overall, and the fights that did occur were less violent - as measured by how often the monkeys got badly bitten.
In other words, even biased interventions seem to play a 'policing' role in these monkeys. Impartial interventions did occur, but were much rarer, and normally only used to quell the most vicious of fights. Perhaps, in these circumstances, the high-ranking monkeys simply had to treat both sides equally, because neither was going to back down if they didn't. But, in less violent situations, they could attack the aggressor, and get him to stop, much as a human policeman might treat a mugging differently than a drunken brawl. The researchers argue, therefore, that, contrary to the usual definition, just because an intervention is biased, that doesn't mean it isn't a police action of some kind.
Humans are, biologically speaking, a special kind of monkey. We owe our success, in part, to our ability to form vast and complex social networks that can achieve more together than individuals can on their own. Certainly, members of our species can be pretty mean to one another, and bloodshed is common in the world. But we do have mechanisms to limit it, and some of them may date back to our distant ancestors.
[Photo by George Gallice.]