The Unexpected Reason Baboons March in Order

Baboons have long puzzled scientists with their habit of walking in neat lines across the African landscape. Were they protecting the vulnerable, following leaders, or competing for food?

A Swansea University team used high-resolution GPS to track wild chacma baboons and tested these theories.

Why Baboons Walk in Lines

Scientists at Swansea University have found that baboons line up while walking not as a defense tactic or strategic move, but simply to remain near their closest companions.

These primates often move in organized formations called ‘progressions’ when traveling through their habitat. Past research struggled to agree on why they do this. Some suggested the order was random, while others believed it was deliberate, with the most vulnerable animals kept in the middle to reduce danger from predators.

To investigate further, Swansea researchers used high-resolution GPS devices to track a troop of wild chacma baboons (Papio ursinus) living on South Africa’s Cape Peninsula. The results, published in the journal Behavioral Ecology, showed that the patterns of movement were shaped by social connections rather than by efforts to avoid threats.

Testing Four Hypotheses

The team analysed 78 travel progressions over 36 days and showed that the order in which the individual baboons traveled was not random.

The researchers tested four potential explanations for the baboon progression order:

1. Protecting the vulnerable (risk hypothesis)
2. Competing for resources (competition hypothesis)
3. Following leaders (group decision-making hypothesis)
4. Patterns emerging from social relationships (social spandrel hypothesis)

After analyzing the data, the researchers found that the baboons’ movement patterns were driven solely by their social relationships.

Not Leaders, Just Friends

Dr. Andrew King, Associate Professor at Swansea University, said: “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 like we see in the movements of plains zebra. Instead, it’s driven by who they’re socially bonded with. They simply move with their friends, and this produces a consistent order.

“In the baboon group we studied, the more socially connected, higher-ranking individuals usually walk in the middle of the group, while lower-ranking baboons are often out in front or at the rear. During these group movements—like heading to a familiar sleeping spot—it’s likely that the group already knows where they’re going. So, the baboons at the front aren’t really leading; they’re just out ahead.”

This map shows the movement of baboons across their habitat, with each dot representing an individual’s location. Colors indicate dominance level—purple (low), pink, orange, and yellow (high)—revealing how individuals of different ranks travel and cluster together. Credit: Dr. Andrew King

The ‘Social Spandrel’ Effect

This finding introduces the concept of a ‘social spandrel’. In buildings, spandrels are the triangular spaces that emerge as by-products when arches are placed side by side. In biology, a spandrel refers to a trait that arises not because it was directly selected for, but as a side effect of something else. In this case, the consistent travel patterns among baboons emerge naturally from their social affiliations with each other, and not as an evolved strategy for safety or success.

Marco Fele, the study’s lead author and PhD student at Swansea University, said: “We know that strong social bonds are important for baboons – they’re linked to longer lives and greater reproductive success. But in this context, those bonds aren’t serving a specific purpose. The travel order we see is simply a by-product of those relationships, not a strategy with immediate benefits. Our study highlights the potential for these kinds of spandrels in collective animal behavior.”

Reference: “Baboon travel progressions as a “social spandrel” in collective animal behaviour” by M Fele, I Fürtbauer, M Lurgi, M Papadopoulou, A M Bracken, C Christensen, M J O’Riain and A J King, 11 March 2025, Behavioral Ecology.
DOI: 10.1093/beheco/araf022

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