Jane Goodall, one of the most active primatologists who demonstrated how similar chimpanzees’ behavior is to that of humans, died today at the age of 91.

The Jane Goodall Institute stated that the British scientist passed away of natural causes while she was in California as part of her lecture tour in the United States.

Her discoveries, as ABC emphasized, revolutionized science, and she was a tireless advocate for the protection of the environment.

Her interest focused on primates, a large family of mammals that includes gorillas, monkeys, chimpanzees, and humans. These species are our closest relatives on the evolutionary tree.

In July 1960, at the age of 26, Goodall began her research on chimpanzees in the wild in Tanzania. During her study, she demonstrated that these primates display a range of behaviors similar to those of humans, such as communication, the development of individual personalities, and the creation and use of their own tools.

“Their behavior—with their gestures, kisses, hugs, hand-holding, and pats on the back—is so similar to human behavior,” she once said. “They can be violent and brutal and wage a kind of war, but they can also be affectionate and altruistic.”