Whether it’s choosing a Friday night restaurant or un-electing an orange president, reaching a group decision will always be an everyday struggle in the human social world. To weave consensus, we must bargain, persuade, discuss and occasionally threaten until some decision is met. As the 2020 hit online game “ Among Us” demonstrates, it can frequently end in regret and innocent friends being thrown out of airlocks.
This is because consensus, like any average, becomes complicated when the group has to deal with conflicts of interest. Take a simple model of a herd of deer and two patches of food. Our deer need to stick together because a herd of many eyes is a safer place when there are hungry mouths full of sharp teeth around.
If all the deer like the same patch of food, they just head there and there is no conflict of interest. The group decision = the decision of every individual in the herd. However, if most like patch A, but some prefer patch B, then the herd splits into smaller groups which are easier to sneak up on. This is “Combined Decision”, where the group decision is simply the sum of its individual decisions with no group consensus.
Groups that work by Combined Decision are generally common to social systems like herds, shoals and flocks. For example, as shown in a study on Bison using GPS tracking collars by Conradt and Roper (2005), individuals generally stay with their group if it is made up of familiar animals who might have a better idea of where the best food patch is. The Bison show no consensus on where to go; individuals bud off if it seems most profitable to them.
However, a troop of baboons will function differently. A similar GPS tracking study on wild Olive Baboons (Papio anubis, named after the Egyptian god of death) shows that they move in a way more suggestive of a basic consensus. If two individuals began leading the group in different directions, the group splits but starts switching to the leader that has more followers – the trend gets stronger as majority party grows.
If the two leader’s path is split by more than 90 degrees, then the group normally separates. If the leaders’ direction is closer than 90 degrees then the group moves in average middle path. Olive Baboons have clear social hierarchies, but interestingly this does not appear to influence which leader to follow as much as the consensus for the group to head in the direction favoured by most individuals.
This subtle form of consensus has been demonstrated in homing pigeons. A study by Jorge & Marques (2012) on domestic pigeons (Colomba livia) shows that when they travel in flocks of three, the direction they take is an average for the knowledge of the flock. The birds reach a consensus direction as an average of the three directions each had programmed into its homing behaviour. In these birds, dominance is a factor. Older birds have a greater influence on the flock direction, but still consider the knowledge of their wing mates – making them a somewhat democratic leader.
The best example of a true group consensus is shown by the African Painted Dog, Lycaon pictus. These wild dogs are highly sociable, forming large packs led by a dominant breeding pair. A study by Walker et al (2017) shows they make votes by sneezing. These sneezing rallies begin while the dogs are resting, and if enough dogs sneeze then a consensus is met and the pack moves out. The first rally rarely gets the group going, but with each consecutive rally it became more likely – and rallies initiated by the dominant pair only need three agreeing sneezes to be a consensus.
Rallies started by subordinates, however, need around ten agreeing sneezes to get a consensus, but regardless of whoever starts it, the dominant pair always choose which direction to head.
This might not be the only example of this type of voting in painted dogs. In the BBC series “Dynasties” they were observed to use a unusual singing call to choose a new dominant pair, after the predecessors were eaten by lions (https://www.bbc.co.uk/programmes/articles/5PzDGbzbX874n2N4BN73TSD/painted-wolves-sing-to-choose-a-new-alpha-pair). However there has not yet been any scientific study investigating this particular behaviour.
Overall, we might consider the cooperative decision of civilisation a unique feature of human beings – but many animals live in social groups, and within those groups lie many features which we recognise in our own social lives.
Conradt, L. and Roper, T.J., 2005. Consensus decision making in animals. Trends in ecology & evolution, 20(8), pp.449-456.
Merkle, J.A., Sigaud, M. and Fortin, D., 2015. To follow or not? How animals in fusion– fission societies handle conflicting information during group decision‐making. Ecology letters, 18(8), pp.799-806.
Strandburg-Peshkin, A., Farine, D.R., Couzin, I.D. and Crofoot, M.C., 2015. Shared decision- making drives collective movement in wild baboons. Science, 348(6241), pp.1358- 1361.
Jorge, P.E. and Marques, P.A., 2012. Decision-making in pigeon flocks: a democratic view of leadership. Journal of Experimental Biology, 215(14), pp.2414-2417.
Walker, R.H., King, A.J., McNutt, J.W. and Jordan, N.R., 2017. Sneeze to leave: African wild dogs (Lycaon pictus) use variable quorum thresholds facilitated by sneezes in collective decisions. Proceedings of the Royal Society B: Biological Sciences, 284(1862), p.20170347.