Animals regularly make group decisions that directly affect their everyday lives. But without the convenience of machines or ballots, how do they vote?
Last week, citizens of the United States voted to select who they thought would best serve them as President of their country, as legislators for their states, and more. They filed into their polling places (many of them waiting for hours), and indicated their choices on a touch screen or by colouring in ovals on a response form. Each voter weighed up the multiple consequences of each option and, after careful consideration, reached a conclusion. Then, each individual's personal decisions were counted, and out of the chaos a winner emerged.
Animals make collective decisions, too. While non-human species typically don't vote to choose their leaders, they do vote for other more routine decisions, like where to live or where to forage. But they don't have voting machines or ballots to determine the group's consensus, so how do they do it?
Some do it through the wisdom of crowds. Near the end of spring or the beginning of summer, honey bee (Apis mellifera) colonies grow too large for their hives, so the group splits in two. The mother queen and half of the worker bees leave the hive to seek a new location, while the daughter queen and the remaining workers remain in place. Minutes later, the departed group identifies a temporary resting place on a nearby tree branch, and from there it surveys the local real estate. Several hundred scouts fan out in all directions in search of a suitable location for a new hive. On their return, each scout communicates the location of the space they found by performing a waggle dance in front of their hive mates.
Over the course of several days, the scouts may spend as much as sixteen hours dancing, each advocating for a possible location. As the days pass, consensus begins to emerge. It isn't entirely clear what makes scouts stop campaigning for less popular sites; they don't get voted out as if they were participating in some insect version of Dancing with the Stars. Some simply stop dancing, while others switch their choreography to endorse one of the more popular options.
What is clear, however, is that the “hive mind” can make complex decisions only because the work is distributed across multiple individuals. Thomas Seeley and Susannah Buhrman, who have studied decision making in swarms of honey bees write, "we have seen that there is no omniscient supervisory bee that compiles all the evaluations and selects the best site. Instead, it is the highly distributed process of friendly competition among the scout bees that identifies the best site. Hence the cognitive effort that each scout bee must make is evidently quite small relative to the information processing done by the entire swarm."
For honey bees, few individuals possess valuable information, which the rest of the group relies on. However, social species throughout the animal kingdom often have to make decisions without the aid of expert knowledge. Such is the case for Tonkean macaques (Macaca tonkeana), a group of fruit-loving monkeys that live in the forests of Sulawesi, Indonesia. Fruit trees are distributed randomly throughout the forest, with some areas containing more fruit than others. So Tonkean macaques must decide which direction they will move in search of food, and they make those choices by majority vote.
When a particular Tonkean macaque wishes to move the group, he or she walks a few steps in the desired direction, pauses, and then turns his or her head back towards the rest of the group. This indicates that the group should move to a new food patch. The other monkeys then decide whether to support the direction suggested, or whether to offer an alternative. If an alternate direction is proposed, each group member votes by joining with his or her favoured candidate. Like the leader himself, they walk a few steps, pause, and then turn their heads back to inspect the rest of the group.
Once the majority of the group has voted, the remaining undecided voters simply side with the majority, walking along but not turning back to monitor the others. Those who opted for the losing recommendation turn around and catch up the group.
Like most primates, Tonkean macaques maintain a strict social hierarchy, but all group members vote when it comes to these sorts of decisions. And any individual may act as initiator, regardless of age, sex, or hierarchical status. By contrast, it is primarily the older or more dominant individuals who make decisions for other monkey species, such as the closely related rhesus macaques.
Democracy in this form is not limited to primates. African buffalo (Syncerus cafer) are large bovines distantly related to domestic cows that can be found grazing in forests, grasslands and swamps across the African continent. Food patches vary for African buffalo, based on previous grazing history by the herd as well as by other species, on the speed at which plants regrow, and on soil quality – not to mention the amount of time it would take them to get there.
Writing in The American Naturalist, David Sloan Wilson quotes a buffalo expert named H. H. T. Prins, who wrote about an odd pattern in which the females get up while at rest, shuffle around, and lay back down. "[A]t first I interpreted this as “stretching the legs”, but one day I noticed that the cows adopt a particular stance after the shuffling and before lying down again,” he wrote. “They seem to gaze in one direction and keep their head higher than the normal resting position but lower than the alert… This standing up, gazing and lying down behaviour continues for about an hour, but the overall impression remains that of a herd totally at rest." Wilson notes that Prins spent two years watching the buffalo before realising that this simple stretching behaviour was actually a means of registering one's vote. Prins continues (as quoted by Wilson): "A few moments later, everywhere in the herd buffalo start trekking. The exciting thing is that they start trekking, at the beginning independently of each other, in the same direction."
Rather than simply shifting positions to become more comfortable, the female buffalo were actually casting their votes to indicate the direction they wished to travel. And the direction that the herd ultimately chose to move could be successfully predicted by the number of individuals who had initially been gazing that way. In other words, herd movements are guided by majority vote. If the votes were evenly divided between two directions, then the herd separates for the night, grazing at different locations, and reconvenes in the morning.
Unlike the Tonkean macaques, only the adult female African buffalo are allowed to vote. But like the monkeys, all adult females vote regardless of their position within the dominance hierarchy. Also like the monkeys, any female may propose a travel route.
One thing animals don't appear to do, though, is explicitly select their leaders, as humans do. For elephants, it’s automatically the oldest female. Chimpanzees are led by the male who is able to retain hold over his position as most dominant. A female honey bee becomes queen based on what she eats in the first days of her life (though worker bees do seem to have some influence over who becomes queen, giving honey bees the most human-like election process).
But group decision-making is not unique to our species. Even the smallest worker bee, the youngest Tonkean macaque, and the least dominant African buffalo get an equal say in making group decisions that directly impact their own survival. Democracy, it seems, is far from being uniquely human.