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This suggested that upright walking had developed long before larger brains.She “had a tiny brain,” Johanson later wrote in his 1981 book on Lucy, “and yet walked erect…here was an ape-brained little creature with a pelvis and leg bones almost identical in function with those of modern humans.” Equally remarkable was how old she was.But when he took a closer look, he saw that many of her features were significantly more primitive than other Australopithecine specimens. The duo compared Lucy to a so-called “First Family” of some 13 other skeletal remains found at Hadar as well as to a collection of hominid footprints excavated by famed anthropologist Mary Leakey in Laetoli, Tanzania.

The headline-grabbing find filled in crucial gaps in the human family tree, but it also shook up ideas about early human evolution and upright walking.

Forty years later, learn the story behind the fossil that permanently changed scientists’ understanding of human origins. Donald Johanson woke up on the morning of November 24, 1974, feeling lucky.

While hunting for fossils in Ethiopia’s Afar Triangle on November 24, 1974, paleoanthropologist Donald Johanson and graduate student Tom Gray stumbled upon the partial remains of a previously unknown species of ape-like hominid.

Nicknamed “Lucy,” the mysterious skeleton was eventually classified as a 3.2 million-year-old “Australopithecus afarensis”—one of humankind’s earliest ancestors.

In this regard, Lucy was like nothing the researchers had ever seen.

Anthropologists had often speculated that erect posture had developed as hominids evolved larger brains, but Lucy’s brain was only the size of a grapefruit—roughly as big as a chimpanzee’s.

“I felt it was one of those days…when something terrific might happen.” Ignoring the already scorching heat and the mountain of paperwork on his worktable, Johanson hopped in a Land Rover with Gray and made the four-mile journey to a gully on an ancient, dried out lakebed.

Before he left, he made a brief note in his journal: “To Locality 162 with Gray in AM.

After a few hours of scouring the sunbaked ground, they decided to take a detour through a nearby gully for one last look.

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