In 1974, Jane Goodall witnessed a disturbing scene in Gombe Stream National Park, Tanzania. A gang of male chimpanzees invaded their neighbors’ territory and attacked a male chimp sitting by himself in a tree. The intruders dragged the chimpanzee to the ground, pinned him down, and bit and hit him all over his body. The attack ended when one member of the gang threw a rock at the bleeding victim. The battered chimp was never seen again and presumably died from his injuries.
The murderous chimpanzees weren’t attacking a stranger: They had recently all belonged to the same group. When the group split in two, one community took over the northern half of the range and the other the southern half. From 1974 to 1977, during the “four-year war,” the northern males obliterated the southern community, hunting down and killing all of its adult males. The northerners took over their enemies’ territory and females.
This was the first time scientists had documented “warfare” among chimpanzees. It wasn’t the last.