France, May 10 -- The clashes, known as the Ngogo conflict, are the focus of a major study published in April in the journal Science, based on three decades of research.

Researchers say the violence grew out of a single chimpanzee community that gradually divided into factions in Kibale National Park, a process that began in the late 1990s and became more pronounced around 2015.

The divide deepened after the birth of the last infant linking the two groups, after which they formed separate social circles and had less and less contact.

Scientists now identify the two sides as a "central group" and a "western group" - with both organising patrols across their territory.

Over time, the bonds within each group grew stronger as relations be...