At the border of a dangerous territory, a troop of about 30 individuals involved in a border patrol climbs a rocky hill to carry out reconnaissance. Detecting the sounds of opponents who appear to be very close, the squad retreats. There’s no reason to risk a fight when the odds are against you.
It is a scenario that has played out countless times in the history of human warfare. But in this case, it didn’t involve people, but rather chimpanzees in Taï National Park, in southwestern Côte d’Ivoire, the largest protected area of rainforest in West Africa.
Researchers said Thursday that they have documented the tactical use of high ground in wartime situations by observing two neighboring communities of wild western chimpanzees daily in Taï National Park for three years.
Information obtained during hilltop reconnaissance determined whether the chimpanzees carried out incursions into enemy territory, according to the study. The animals seemed more likely to do this when the risk of confrontation was lower.
The study, according to the researchers, records for the first time the use of this human military strategy by the closest living relatives of our species.
“This shows sophisticated cognitive and cooperative abilities to anticipate where and when to go, and act on the information collected in a safe way,” said Sylvain Lemoine, a biological anthropologist at the University of Cambridge and lead author of the study published in the journal PLOS Biology.
Episodes of violence between groups are recurrent in the case of chimpanzees, said Lemoine. Clashes occasionally occur in overlapping border areas.
“Chimpanzees compete for space, which includes food sources. Large territories bring more benefits as they reduce competition within the group, and female reproductive rates are higher in larger territories,” said Lemoine.
The two neighboring groups tracked in the study were similar in size, between 40 and 45 individuals, with around 5 to 6 adult males and 10 to 13 adult females, with the remainder being adolescents, juveniles and cubs. Males are always dominant over females, the researchers said.
“Chimpanzees are extremely territorial. They carry out regular border patrols, roaming the territory in a coordinated and cohesive manner,” said Lemoine.
“They engage in intergroup encounters that are violent, dangerous, and stressful. These encounters may be long-distance vocal exchanges, eye contact, or physical contact with fights, bites, and chases. Murders are common, and victims can be of all stripes. ages”, added Lemoine.
Climbing hills does not necessarily improve the visual identification of members of a rival community, but it does offer better acoustic conditions for detecting opponents by sound.
“The hilltops are covered in vegetation and don’t offer good vantage points,” Lemoine said.
When at the top of the border hill, chimpanzees generally avoid making noise when eating or looking for food. They seek to rest and listen.
They were more likely to advance into dangerous territory after descending a hill if rival chimpanzees were further away. These incursions occurred approximately 40% of the time when rivals were about 500 meters away, 50% when rivals were about 1 km away, and 60% when rivals were about 3 km away.
Chimpanzees and bonobos are the species closest genetically to humans, sharing around 98.8% of our DNA. According to research published in June, human and chimpanzee evolutionary lineages separated about 6.9 million to 9 million years ago.
Studying chimpanzee behavior can offer clues about our own species.
“We can better understand where we came from and what makes us human. We can better understand what types of behaviors and adaptations were present in the last common ancestor of humans and chimpanzees, and have a better idea of the sociality and behavior of ancient hominid species,” said Lemoine, referring to extinct species in the human lineage.
“It also teaches us what we have in common with our closest living relatives, how similar we are to wild animals, and that we only differ from our cousins in degree, not in nature,” Lemoine added.