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.
When an American graduate student named Tom Gray announced he was leaving to scout out a nearby fossil site, Johanson had a hunch he should tag along.
“I felt a strong subconscious urge to go with Tom,” he later wrote.
“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.