Researchers have found that macaques groups rapidly descent into violent chaos if several of the dominant males are removed. These dominant males act like some form of police force and keep the cohesion of the group and defuse conflicts before they turn ugly.

The dominant males usually patrol the herd and collect signs of respect (i.e. bared teeth gestures) from the other subordinate monkeys and intervene in impending conflicts.

Jessica Flack of the Santa Fe Institute in New Mexico, US, and her colleagues temporarily removed three out of four dominant males from a captive group of 84 pigtailed macaques at the Yerkes National Primate Research Center. They wanted to know what would happen when the "police" are missing.

What happened was that the group rapidly began to segregate into smaller groups. Communal activities like playing, grooming and sitting together also stopped, and the groups engaged in violence. The researchers didn't let the situation go on to see whether the groups would eventually reunite, and they reintroduced the dominant males whom brought back the peace.

"In our macaques, a few individuals were perceived as disproportionately powerful. These animals are recognised as being very capable of using force successfully," says Flack. "One of the important implications is this feedback between power structure and social network structure".

Another member of the research team, Frans de Waal at the Yerkes Primate Research Center, Emory University notes: "We tend to associate power with privilege, but both in human and animal society it also entails a constructive contribution, or at least ought to. Through their stabilizing presence and active peacekeeping, the dominant males contribute to a more cooperative society."

This is indeed what historically happened to human societies as well. Both aggressive and cooperative behaviors are natural behaviors. The "human nature" is not exclusively dominated by either one. Thus, what happened historically was that people engaged in both types of activities and some proved better at aggression than others. These people became the tribe leaders. Their activity was partially exploitative: they used force to get from others certain kind of benefits and privileges.

Later on, as the tribes got bigger the leaders hired helpers. At first, the helpers were family members and their jobs were not specific - they all did the same tasks: police the group, steal part of the subordinates' incomes (i.e. collected taxes) etc. As the tribes got bigger and the helpers got more numerous the leaders became more and more exploitative. At first, there was little difference from what they did and what the rest of the tribe did; later on the differences got sharper and the leaders got less and less productive and focused more and more on the aggressive job.

Finally, later still, the leader's helpers got specific jobs: some of them would only collect takes, some of them would only police the group, some of them would only be witch doctors etc. This is the point when one could say the state has appeared, and the state institutions have appeared.

However, as this study on the macaque monkeys shows, the leaders also play a benefic social role (although not necessarily on purpose). By imposing a monopoly of aggression they diminish the aggressive behaviors of their subordinates - they diminish the aggressiveness their subordinates would otherwise have towards one another.

In case of human societies this beneficial effect of the monopoly of aggression has always been postulated by various political thinkers and denied by others. Only extremely rarely historians have had the opportunity to actually observe what happens if the power of the state is disbanded. Certain events such as the instauration of anarchy in various parts of Spain during the Spanish Revolution are sometimes quoted, but these events always happened in critical conditions and their relevance has been controversial.

But if we are not that different from these monkeys this study also offers some insight into the distant past of human societies.