The very human reason why baboons walk in lines

Baboons walking in progression on South Africa’s Cape Peninsula (Vittoria Roatti)

A new study is challenging long-held assumptions about animal movement, suggesting that baboons don’t march in line to protect themselves or to follow a leader, but rather, to stay close to their friends.

Published in Behavioral Ecology, the peer-reviewed study, led by researchers at Swansea University in the U.K., found that social bonds – not strategy – best explain why wild chacma baboons form consistent travel lines during group movements.

In other words: the animals are walking in line because they just want to hang out with their friends.

The researchers tracked 25 wild baboons in South Africa over 36 days, using high-resolution GPS collars to record 78 travel progressions, also known as “lines,” formed as the baboons moved across the landscape.

The team tested four potential patterns: predator avoidance, food competition, dominance hierarchy, or social relationships. The data pointed to the fourth option.

Julie Teichroeb, primate researcher and associate professor at the University of Toronto Scarborough, says this doesn’t come as a surprise.

“For a long time, it was this idea that big males, especially in baboons, are at the head and back of the group, protecting everyone within the group,” Teichroeb told CTVNews.ca in an interview Thursday. “I’m glad someone showed it’s not a selected kind of organization. They leave in groups because they’re hanging out together.”

Teichroeb said that despite the limited study duration, multiple movements were observed each day and a pattern was spotted quickly.

This finding reframes how scientists understand certain group behaviours in the animal kingdom.

Traditionally, linear movement in animals, especially in open terrain, has been seen as a defensive formation, with stronger members shielding the more vulnerable. But in this case, researchers found no evidence that the line formation had a survival function.

“It shows how important these social bonds are. The immediate individuals around (them) is really important,” Teichroeb said.

Teichroeb says the idea of travel lines is visible in other primate species, like Vervet monkeys, which Teichroeb studied in Uganda.

“Groups of related females and their kids, they’re all leaving around the same time, and they’re sort of clustered together,” she said.

‘Social spandrel’

The researchers proposed that the baboons’ behaviour is an example of “social spandrel” – a concept borrowed from evolutionary biology and architecture.

A “spandrel” refers to a feature that arises as a byproduct of something else, rather than a functionally selected trait. In this case, travel lines are an incidental result to strong social bonds. Social relationships serve as an evolutionary function, the study suggests.

Teichroeb references the critical approach of evolutionary biologists like Stephen Jay Gould and Richard Lewontin, who argued that not everything has an evolutionary purpose and many things are a secondary byproduct of something else.

The study also found that dominant and well-connected baboons consistently held central positions in the line – not because they were leaders or protectors – but because they simply had more social connections, and those connections pulled them inward from multiple directions. Subordinate or less social baboons tended to be at the edges.

As for the methodology, Teichroeb said for these studies, GPS devices can give detailed, second-by-second updates on primates’ movements.

“It’s a lot more than we can do in the field with our eyes,” Teichroeb added.

She also warned that studies that heavily rely on GPS points and don’t follow animals suffer from a lack of context in social cues and faces.

The findings contribute to a growing field of social movement ecology, which studies how social relationships shape group dynamic in animals. While many species move in coordinated ways for protection or efficiency, the study underscores the need to look deeper into the social drivers of those patterns.

It also raises the question about how friendship and social bonding influence animal behaviour in subtle ways, including how groups form, travel and make collective decisions.

As for further studies, Teichroeb said finding out if this is a species-wide pattern would be insightful.

“It would be neat to see if this is something that emerges in matrilineal species that are really tight female kin groups, or if it emerges in more loosely bonded species that don’t have kinship within the group,” Teichroeb suggested.

In the end, researchers hope their work will help scientists rethink assumptions about the “why” behind animal movement. In some cases, the answer may not be life-or-death, just heart-to-heart.