Gorillas Live in Tribes and Have 'All-male Bachelor Groups,' Scientists Discover

Scientists who studied gorillas in jungle clearings say the animals have complex hierarchical societies similar to humans.

We humans live in complex social structures, which are thought to have emerged as small autonomous groups grew into networks made of multi-layered hierarchies. Scientists believe humans have what is known as a unique "social brain." It is thought these formed as our brains grew after the chimpanzee-human split.

Dr. Robin Morrison, a biological anthropologist at the University of Cambridge, and her team believe complex societies could have evolved earlier than previously thought.

To arrive at their conclusion published in the journal Proceedings of the Royal Society B, the team studied the interactions of hundreds of western gorillas in forest clearings in the Republic of Congo. The animals were drawn from relatively long distances to the spots packed with mineral and protein-rich vegetation, where they fed for hours at a time.

Similar to some traditional human societies, groups of western gorillas tend to feature one male and one or more females with dependent offspring who leave when the unit when they reach sexual maturity. It can take years for males to find their long-term mates. And unlike chimpanzees who are territorial and violent, western gorillas often share areas with other groups and meet at resource hot spots—just like humans, the authors wrote.

The team looked at data collected over a 409-day period between April 2001 to September 2002 at the Lokoué clearing in Odzala National Park, where 205 gorillas part of 48 groups were observed. The sample also included observations from the Mbeli Bai clearing in the Nouabalé-Ndoki National Park between January 2010 to December 2015, visited by 271 individuals in 44 units.

Morrison explained in a statement that studying the social lives of gorillas can be tricky, as they spend most of their time in the dense forest, and it can take years for them to get used to and act naturally around humans.

"Where forests open up into swampy clearings, gorillas gather to feed on the aquatic vegetation. Research teams set up monitoring platforms by these clearings and record the lives of gorillas from dawn to dusk over many years," she said in the statement.

gorillas, republic of congo, socialising, cambridge
Young gorillas take a break from feeding to socialize at the Mbeli Bai forest clearing in the Nouabale-Ndoki National Park, Republic of Congo. Wildlife Conservation Society

The researchers found that the animals not only interacted with their immediate families, but also an average of 13 extended family members—comparable to grandparents and aunts. What's more, each individual had a further extended group of around 39 gorillas who weren't necessarily related, but with whom they spent time.

"An analogy to early human populations might be a tribe or small settlement, like a village," Morrison said in a statement. Sometimes, males who left their families at similar times found strength in numbers by forming "all-male bachelor groups."

Morrison told Newsweek: "Not only do gorillas appear to have preferences in which other groups they interact with, but these seem to be highly consistent over time—analogous to human friendships.

"The underlying social structure found in gorillas also closely resembles that in humans where multiple levels of social affiliation are found, going from strong friendships with a small number of individuals to larger groups of acquaintances or extended family. It suggests that the origins of the underlying social structure in humans, which is integral to our complex and cooperative society, has far earlier evolutionary roots than we previously thought."

Morrison told Newsweek she was surprised by quite how consistent the gorillas were with their interactions over time.

"A lot can change in a gorilla population in just a few years, new groups form, females leave one group and move to another, other groups may stop visiting the clearing entirely, but despite this there still remained clear preferences," she said.

The most challenging part of the study, Morrison told Newsweek, was identifying all the different gorillas that visited the forest clearing over many years.

"Over 450 different gorillas have visited the clearing since monitoring began in the 90s and recognizing them from sometimes more than 100 meters away takes a lot of skill but is vital to understanding the social interactions taking place," she said.

To get around this, the team used spotting scopes, binoculars and a camera with a very large zoom. And before joining the team, researchers had to complete a painstaking training program to learn the distinctive features of the different gorillas such as face shapes, and patterns around the nose and eyes, she explained. The process took many months.

Dr. Nicholas E. Newton-Fisher, reader in Primate Behavioural Ecology at the University of Kent, who was not involved in the research, told Newsweek "the study highlights the need for consideration of both gorilla and chimpanzee biology when looking to understand the evolution of hominins, and of our own social systems."

Highlighting what he regarded as limitations of the work, Newton-Fisher said: "The study relies on a measure of association that is quite 'loose' - i.e. appearing in the same, large, clearing on the same day.

"This doesn't require close proximity, social interaction or even for the gorillas to be present at the same time, and is quite different from how association would be recorded in other species, such as chimpanzees. The study also relies on individuals being drawn to feed on a common resource, where their association patterns may not reflect what happens when away from these clearings."

He also stressed: "We need to remember that neither chimpanzees nor gorillas are direct analogues for particular hominin species, and within hominins—our own branch of the evolutionary tree after our common ancestor with chimpanzees (and bonobos)—there was a diversity of species."

"We can't simply jump from either gorillas or chimpanzees to any particular species of hominin, or to ourselves. Instead, what we need to do is to understand the reasons natural selection has produced particular social structures in order to understand the reasons behind our own social systems."

Gorillas Live in Tribes and Have 'All-male Bachelor Groups,' Scientists Discover | Tech & Science