Nov 2 – On the boundary of dangerous territory, a troop of about 30 individuals engaging in a border patrol climbs a rocky hill to conduct reconnaissance. The squad fled when they heard sounds that were a little too close. It is not worth risking a fight when the odds are against you.
It is a scenario that has unfolded innumerable times in the history of human warfare. But in this case, it involved not people but chimpanzees in Tai National Park in southwestern Ivory Coast, West Africa’s largest protected area of rainforest.
Researchers said on Thursday they have documented the tactical use of elevated terrain in warfare situations while observing on a daily basis two neighboring communities of wild western chimpanzees in Tai National Park for three years.
Information obtained during hilltop reconnaissance shaped whether the chimpanzees made forays into enemy territory, the study found, with these apes appearing more apt to do so when the risk of confrontation was lower. Researchers said that the study records the use of an age-old military strategy used by humans and our closest relatives for the very first time.
“”It shows sophisticated cognition and cooperation skills in anticipating where to go and how to do it in a safe manner,” explained University of Cambridge bioanthropologist Sylvain Lémoine. The study was published in the Journal PLOS biology .
Inter-group violence is ubiquitous in chimpanzees, Lemoine said. Skirmishes occasionally occur in overlapping border areas.
“Chimpanzees compete for space, which encompasses food resources. Lemoine stated that larger territories were beneficial because they reduce competition within groups and increase female reproduction rates.
The two neighboring groups tracked in this study were of equivalent size, between 40 and 45 individuals, with about five to six adult males and 10 to 13 adult females, the rest being adolescents, juveniles and infants. Males are always dominant over females, the researchers said.
“Chimpanzees are extremely territorial. They undertake regular border patrols, where individuals roam in the periphery of their territory in a very coordinated and cohesive way,” Lemoine said.
“They have violent and dangerous inter-group confrontations. Inter-group interactions can include vocal exchanges at a distance or visual contact, as well as physical encounters with bites, fights and chases. Lemoine said that killings occur frequently and can affect people of all ages.
Climbing hills does not necessarily improve visual detection of members of a rival community, instead offering improved acoustic conditions to detect adversaries by sound.
“The hills are overgrown with vegetation, and therefore do not provide good lookouts,” Lemoine explained.
While atop the border hills, chimpanzees usually avoided noisy eating and foraging in favor of resting or listening.
They were more likely advance into danger territory after descending from a hill, if rival chimpanzees are further away. Such incursions occurred approximately 40% of the time when rivals were about three-tenths of a mile (500 meters) away, 50% when rivals were about six-tenths of a mile (1 km) away and 60% when rivals were about 1. 9 miles (3 km) away.
Chimpanzees and the closely related bonobos are the species nearest genetically to humans, sharing about 98. 8% of our DNA. The human and chimpanzee evolutionary lineages split about 6. 9 million to 9 million years ago, according to research published in June.
Studying chimpanzee behavior may offer insight into our own species.
“We are able to better comprehend where we came from, and what it is that makes us humans. We can better understand which kind of behaviors and adaptations were present in the last common ancestor between humans and chimpanzees, and have a better idea of the sociality and behavior of ancient hominin species,” Lemoine said, referring to extinct species on the human lineage.
“It also teaches us what we have in common with our closest living relatives, how similar we are with wild animals, and that we only differ from our cousins in degree and not in nature,” Lemoine added.
Reporting by Will Dunham in Washington, Editing by Rosalba O’Brien
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