Mountain gorillas have their own strategy to avoid inbreeding

In many animal societies, individuals of one sex, or sometimes both, eventually leave their birth group to join another. In a smaller number of species, including humans and gorillas, individuals can change between groups multiple times.

This process, known as dispersal, helps avoid inbreeding, spreads genetic diversity, and shapes social bonds. But how do individuals decide where to go?

A new study from the University of Zurich offers rare insight, thanks to over 20 years of continuous monitoring of wild mountain gorillas in Rwanda by the Dian Fossey Gorilla Fund.

The findings reveal a surprising mix of instinct, memory, and social intelligence guiding these life-changing moves.

Female gorillas dodge certain males

The research shows that female gorillas do not move at random. Group size or sex ratio didn’t seem to sway them. Instead, past social experiences shaped their choices.

Females consistently avoided joining groups that included males they had grown up with, and sought out females they already knew.

Study lead author Victoire Martignac is a Ph.D. student in the Department of Evolutionary Anthropology at the University of Zurich.

“Because female mountain gorillas do not know with certainty who their fathers are, they might rely on a simple rule like ‘avoid any group with males I grew up with’ as the likelihood of them being related will be higher than with males they did not grow up with,” said Martignac.

Interestingly, this rule isn’t about mere familiarity – it’s about context. Because females can disperse multiple times, they will become familiar with many males from different groups, noted Martignac.

“Yet, when choosing their next group, they only avoid males they grew up with. This really tells us that it’s not just who they know that matters but how they know them.”

Females follow old friends

Even more important than avoiding certain males was the draw of known female companions. A shared history appeared to make the daunting leap into a new gorilla group less intimidating.

“Going into a new group could feel pretty scary, with individuals usually entering at the bottom of the social hierarchy. A familiar female might help reduce this, providing a social ally,” said Dr. Robin Morrison, senior author of the study.

“It could also act like a recommendation from a friend – if a female they know has chosen to stay in this group, it could indicate positive things about the group as a whole or the dominant male leading that group.”

The most influential relationships were those where females had spent at least five years together and had seen each other in the past two years.

“Investing in these relationships clearly matters. Spatial separation can be ephemeral with individuals being reunited in the future, easing the difficult process of starting over in a new social group,” said Dr. Morrison.

Gorilla bonds last across groups

These patterns show that dispersal among gorillas is not only about survival and reproduction. It also helps maintain connections that may have formed years earlier.

The fact that individuals move multiple times, and that groups often overlap and interact, means social bonds can extend far beyond immediate companions. This trait is strikingly similar to human societies, where close ties can persist across different communities.

“This is a reminder of the meaningfulness of social relationships kept across boundaries and how this extended network of relationships might have played a key role in the evolution of larger and more cooperative societies,” the researchers noted.

How gorillas avoid inbreeding

Understanding these subtle decision-making patterns isn’t just a fascinating scientific insight – it could influence how conservation programs are designed.

If female gorillas rely on past relationships and familiarity to choose new groups, relocating or protecting these networks could help ensure healthier populations.

By preserving both the habitats and the social structures of these animals, conservationists can support not just their survival, but their well-being.

The research offers a rare glimpse into how memory, trust, and social preference guide one of the most important decisions in a gorilla’s life – when and where to start anew.

The study is published in the journal Proceedings of the Royal Society B Biological Sciences.

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