The ten-year chimpanzee civil war, explained

A 10-year chimp civil war continues with no end in sight. The new study draws from more than 30 years of observations of the Ngogo chimpanzee group in the western forests of Uganda. At its peak, nearly 200 individuals were in the Ngogo group, living cohesively in smaller subgroups that the researchers labeled as "clusters." Males and females from different clusters intermingled. They mated, hunted together and worked together to fight off other outside groups. Researchers took videos of males from different clusters holding hands. Then, in 2015, the researchers started seeing signs that something was off. "I can even pinpoint it to one particular day when there was a really big change," said Aaron Sandel, the lead author of the new study and a primatologist at the University of Texas at Austin. Over the next seven years, the Western group killed at least six other adults and 17 infants from the Central cluster. The fighting continues to this day. Why the Ngogo group split and why its members turned on each other is still unclear. In the paper, Sandel and his co-authors suggest several factors that may have contributed: the size of the group, competition for food and male-to-male competition. The natural deaths of five adult males and one adult female in 2014, before the intergroup divisions took root, may have weakened social networks. Caption from article by Nathan Rott, NPR.