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.