From school kids lining up in the playground, to grown ups shuffling for position in a group photo, sometimes it’s just nice to be next to your friends says Helen Pilcher.
Baboons are no different. A new study in Behavioural Ecology suggests that the monobrowed primates walk in lines, not for safety or strategy, but simply to stay close to their mates.
Baboons are highly social animals, that sleep, feed and socialize in groups of around fifty. When they move around their home range, they often travel in single file lines called ‘progressions.’ But who or what determines the order?
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Previous research has yielded conflicting results. Some studies suggested that the order was random, whilst others suggested that dominant individuals flank vulnerable members to protect them.
To work out what is really going on, researchers studied the movements of a wild troop of chacma baboons (Papio ursinus) living in the Da Gama Park area of South Africa’s Cape Peninsula. Individual animals wore GPS tracking collars, and over 36 days, 78 progressions were recorded.
The order was not random. Higher-ranking individuals tended to walk in the middle of the group, while lower-ranking baboons were often at the front or the rear of the line.
“Surprisingly, the consistent order we see for the baboons we studied isn’t about avoiding danger like we see in prey animals when they position themselves in the middle of their social group, or for better access to food or water like we see in the movements of the plains zebra,” says Andrew King from Swansea University, who studied the animals. “Instead, it’s driven by who they’re socially bonded with.”
The finding confirms the gloriously named ‘social spandrel hypothesis.’ In architecture, spandrels are the roughly triangular spaces that emerge as by-products when arches are placed next to each other. In biology, spandrels are characteristics that arise, not because they are selected for, but because they are a by-product of something else.
In this case, the order of baboons emerges naturally from their social preferences, rather than evolving for safety or success. They simply move with their friends, and this produces a consistent order.
“We know that strong social bonds are important for baboons,” says the study’s lead author, Marco Fele. “They’re linked to longer lives and greater reproductive success. But in this context, those bonds aren’t serving a specific purpose. Our study highlights the potential of these kinds of spandrels in collective animal behaviours.”
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