Chimpanzees in Uganda Fight Each Other

About 200 chimps lived in peace for many years. Then they started fighting.

Scientists saw a violent fight among 200 chimps in Uganda. This happened after many years of peace.

A researcher named Aaron Sandel saw the first chimp get killed.

Sandel knew the killed chimp, Erroll, since he was 12 years old. He watched Erroll grow up.

Sandel saw other chimps he knew attack and kill Erroll.

Sandel studied this chimpanzee fight. Researchers have watched these chimps since 1995.

The chimps live in a forest in Uganda's Kibale National Park. They used to live in different areas but would meet to eat or protect their land.

The chimps worked together and defended their land. This helped them grow in number and expand their territory.

In 2015, researchers noticed a change between two groups of chimps. Sandel was with one group when they heard calls from the other group.

The chimps Sandel was with became nervous and quiet. They ran when they saw the other chimps.

The two groups avoided each other for six weeks. This was the start of a split between them.

Sandel said the split led to the killing of Erroll in 2018. The western group killed 24 chimps from the central group.

Primatologist Iulia Badescu said chimps often fight with outsiders. They don't like strangers.

What's unique about this case is that these chimps knew each other well. They had close relationships.

Badescu said it was shocking to see chimps that were brothers or related turn against each other.

Badescu studied the chimps and saw how mothers cared for their young. She visited in 2013 and 2018 and saw the violence start.

This study is the first to show a group of chimps splitting and turning violent. Jane Goodall saw similar violence in Tanzania.

John Mitani is a co-author of the study. He's a professor and has studied primates.

Mitani wondered how friends could turn into enemies. He said it's hard to understand why they fought.

Mitani said the group might have been too big, with over 200 chimps. This could have led to competition for food and mates.

Mitani thinks competition for food and mates contributed to the split. The group was four times larger than usual.

Sandel pointed out that several older chimps died in 2014. This might have weakened the group's social bonds.

The deaths of older chimps showed how important each individual is to the group. It highlighted the social bonds between them.

There was a change in the dominance hierarchy in the central group. A younger male challenged the alpha male.

Sandel thinks the western group might have sensed tension and pulled away. They didn't want to deal with the hierarchy change.

Sandel said there might be similarities between chimp and human conflicts. But chimps don't have religion or ethnicity like humans do.

Sandel thinks it's troubling that human conflicts might be due to simple rivalries. But it also gives hope for finding ways to peace.

Sandel said recognizing the importance of relationships and reconciling after conflicts could help. Chimps are usually good at reconciling.

Mitani finds optimism in the fact that humans are a cooperative species. We help each other, even if we're strangers.

Mitani said humans can live peacefully with each other. We have aggression and wars, but we mostly live in peace.

Mitani has studied these chimps for 30 years. It's not clear how the violence will end.

Mitani loves some of the chimps, but not all of them. They don't all like him either. It's hard to watch the violence.

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