Often, when we think about war, we think about soldiers taking potshots at each other, tanks rolling through the streets, and jets carpet-bombing enemy targets. In fact, the mere concept of “war” seems distinctly human. It turns out, though, that chimpanzees have their own version.

In the late 1970s, famed primatologist Jane Goodall observed a violent conflict between two communities of chimpanzees in Tanzania’s Gombe Stream National Park. Witnessing this conflict dramatically changed Goodall’s notions about chimpanzees.

Like wars among humans, the Gombe Chimpanzee War was long and brutal, and it was even called the “Four Year War of Gombe” (not surprisingly, because the war lasted for four years). In fact, in the years before the war even started, the two communities of chimpanzees in the area, the small Kahama group in the south and the larger Kasakela group in the north, had already drifted apart and tension between them was rising.

Finally, on January 7, 1974, the tension boiled over into violent conflict. On that day, a party of six adult Kasakela males attacked and killed “Godi”, a young Kahama male, who had been feeding in a tree. This is when the war officially began.

Over the next four years, the Kasakelas would kill the other five Kahama males and one Kahama female. At the same time, they also beat and kidnapped three Kahama females and caused two other females to go missing. As a result, no members of the Kahama community remained. All had become casualties, and the Kasakelas eagerly claimed the Kahama’s former territory as their own.

In her memoir, Through a Window: My Thirty Years with the Chimpanzees of Gombe, Jane Goodall wrote about the event, which had deeply disturbed her:

For several years I struggled to come to terms with this new knowledge. Often when I woke in the night, horrific pictures sprang unbidden to my mind—Satan [one of the apes], cupping his hand below Sniff’s chin to drink the blood that welled from a great wound on his face; old Rodolf, usually so benign, standing upright to hurl a four-pound rock at Godi’s prostrate body; Jomeo tearing a strip of skin from Dé’s thigh; Figan, charging and hitting, again and again, the stricken, quivering body of Goliath, one of his childhood heroes. …

Thus, when we think of war as a distinctly human creation, we must remember that our closest ancestors are no strangers to conflict, and they can be just as brutal as humans. When Jane Goodall herself reported this shocking and disturbing behavior, she was not universally believed because of her tendency to humanize animals. However, later research has supported her accounts, and we now know that, like humans, chimpanzees have a darker side to them.

But, of course, chimpanzees are not all evil, vicious creatures, and they are generally quite docile. For a much sweeter story about the gentle nature of chimpanzees, check out our article about a chimpanzee named Wounda, who hugs Jane Goodall before returning to her forest home.

WATCH NEXT: This Bonobo Starts Fires And Cooks His Own Food