Seemingly peaceful gorillas join 'mobs' and beat up rivals

Mobs of gorillas have been seen attacking lone individuals, which they were not thought to do

Chimpanzees and bonobos are our closest relatives, and gorillas are only a little further away.

But when it comes to violence, there are clear differences between the species. While bonobos are known to live in fairly harmonious societies, the same cannot be said either for us or for chimps.

Humans and chimps are both known to actively seek out and attack others. Our propensity for violence is believed to be part of our evolutionary story.

But what of the final member of the group? The conventional view is that gorillas, like bonobos, rarely turn violent.

A male gorilla will commit the occasional act of infanticide, especially if he is overthrowing another male. But these rare attacks aside, gorillas are thought to be peaceable.

Now a surprising series of observations of mountain gorillas in Africa's Virunga Mountains, published in the journal Scientific Reports, has overturned this view of gorillas.

Groups of males and females have been observed attacking other gorillas on three separate occasions in 2004, 2010 and 2013. The attacks took place in the same population first made famous by primatologist Dian Fossey, who introduced gorillas to the world and revealed their seemingly peaceable nature.

In the first observed attack, a solitary male named Inshuti approached a group of 26 individuals, but was chased off by three males.

When the males caught up with Inshuti, they pinned him to the ground and started to attack. The rest of the group soon followed and the mob started to bite, kick and pull out his hair.

"The alpha male repeatedly sank his teeth into his body and shook his head back and forth, similar to a canid shaking prey," the authors report.

Stacy Rosenbaum of the University of Chicago in Illinois witnessed the attack. She says she was stunned.

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