Living in a group has many perks: all the extra eyes and ears to look out for danger or prey, for instance. As it is inevitable that within a collective there will be disagreements on what to do, there must be a way for a group to resolve these conflicts in order to stay together. All this is straightforward enough in an egalitarian crowd: for instance, in shoals of fish, individuals simply follow the majority of their nearest neighbours. But what happens if a group is hierarchical, as is the case for animals such as hyenas, wolves and us? How are conflicts between the wishes of the majority and those of the leadership resolved?

A recent study published in Science by a team of researchers affiliated with institutions in the US, UK, Panama and Germany has addressed this question by looking at how a primate that lives in hierarchical groups, the olive baboon, moves about across the Kenyan savannah. These apes travel many miles per day in search of food, all the while staying very close to each other. How do they make sure that they stay together?

In order to track the behaviour of a troop at the Mpala Research Centre in which the social dynamics and hierarchy were fully characterised, the team fitted most of the individuals with a high-accuracy GPS collar that recorded their position once every second. They then developed computational tools to crunch the data in order to extract what decisions individuals made in relation to the behaviour of their neighbours. They reasoned that if the social hierarchy within the group influences collective decision making, a dominant individual's movements should be more likely to be mirrored by its neighbours than the movements of a lower-ranking baboon.

However, strikingly, the team found that this was not the case: the dominant male in the troop did not have the highest chance of being followed by its neighbours, nor was there a correlation between the sex of the animal and the likelihood that it would be followed. If the baboons’ collective behaviour is not affected by social hierarchy, could it be shaped by similar mechanisms to those involved in non-hierarchical groups? In this case, previous work on collective movement predicts that an individual faced with two neighbours that go off in different directions makes its decision on where to go depending on how different its neighbours’ directions are: if the difference is small, the animal compromises between the two directions; if the difference is large, the animal chooses one or the other.

The team found that the baboons followed this principle exactly, showing that there is no difference in how hierarchical and egalitarian collectives make decisions. The social status of a baboon therefore has no bearing on whether it acts as a leader during the day-to-day business of wandering around in the search for food. Even though we don't like to think of ourselves as herd animals, our behaviour is very likely to follow similar principles to that of the baboon. However, it is probably safest not to apply these findings to dealings with your superiors just yet.

D. R.
I. D.
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Shared decision-making drives collective movement in wild baboons