Macaques Use Simple Voting Process to Stay Together

two black and white monkeys sit next to each other in the grass

Biological Strategy

Tonkean macaque

Sam Stier

Image: PicksArt / Shutterstock / Some rights reserved

Coordinate by Self-Organization

To create and maintain a healthy community of individuals and ecosystems requires that living systems coordinate their activities. Coordination doesn’t necessarily mean that there’s a leader orchestrating what happens. In nature, coordination is usually achieved through self-organization. In a flock of geese flying in a V-formation, for example, there’s no lead goose controlling where all of the others fly. The flock uses this formation because each goose gains energy from air vortices created by the goose in front of it. The lead goose doesn’t gain that benefit, so when it tires, it moves back and another goose takes the front position.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Macaques use simple, clear, inclusive voting process to stay together as a group

Tonkean macaques live in the forests of the Indonesian island of Sulawesi. They move between food patches seamlessly, without conflict, even while traveling in large bands of up to 30 monkeys. You might think a dominant male makes the decisions about which fruit tree to visit next, but you’d be wrong. Instead, any of the macaques, male or female, young or old, can help make this decision. And the troop arrives at each decision through a consensus by voting.

When a macaque would like to move on to another fruit patch, it signals this to the rest of the troop by stepping towards the direction it would like to go, stopping, and then turning to look back at the rest of the troop. This begins the voting process. At this point, another macaque may move in a different direction, effectively proposing the troop travel towards a different fruit patch. Additional monkeys then join one or the other initiators, casting their vote for one direction or another based on preference and their relationships with the other monkeys in each group. Once a voting monkey stops looking back at the rest of the troop, the voting process is effectively over. The remaining monkeys simply join whichever group is largest. The monkeys that voted for the unchosen route then join the rest of the troop, in order to all stay together.

Simple, clear processes of decision-making, in which all members of a group have the opportunity to voice an opinion, and in which an ultimate consensus can always be formed, can be highly effective in keeping a group together.

Last Updated May 14, 2020

References

“This suggests an influence of the behaviour in the first direction on the second one rather than an independent probability to notify in the second direction.” (Sueur et al. 2011: 1699)

“This result confirms that the first individual notifying in the second direction is influenced by the first individual notifying in the first direction. The third notifying individual, whatever the direction, is influenced by the two first notifying individuals, and so on.” (Sueur et al. 2011: 1700)

“This means that the absolute difference in the notifying individuals between direction 1 and direction 2 only needs to equal 1 or more for the initiator to choose the direction with the majority of notifying individuals.” (Sueur et al. 2011: 1701)

“So, as far as joining a movement is concerned, an individual is first influenced by the quorum of notifying individuals, then by the individuals who have already joined the movement and those with whom he is highly affiliated.” (Sueur et al. 2011: 1701)

“In fact, we found that individuals combined the two processes in a single decision when deciding to join. They consider both the number of notifying individuals and their affiliative relationships with already moving individuals when choosing. The synergy of these two mechanisms allows macaques to consider the growing number of departed individuals and therefore the ineluctability of a collective movement, since groups remain cohesive. This is a modulation between being coordinated with the majority of the group and being coordinated with individuals with whom one has alliances or shares similar motivations.” (Sueur et al. 2011: 1702)

Journal article