In 1974, Donald Johanson and his team found one of the most complete early hominin skeletons known, near Hadar in Ethiopia's Afar Region. She was named "Lucy" — after the Beatles song playing in camp that night — and catalogued formally as AL 288-1. About 40% of the skeleton was preserved: parts of the skull, pelvis, femur, and vertebrae.

Lucy's importance comes from one feature: her pelvis, knee and foot structure were clearly adapted to walking on two legs. Yet her brain volume was around 400 cm³ — close to that of a chimpanzee. This reversed a long-held assumption about human evolution. The brain had been thought to expand first, with bipedalism following; Lucy showed that walking upright was already established millions of years before brain expansion began.

Australopithecus afarensis lived in East Africa from roughly 3.9 to 2.9 million years ago. Footprints stamped into volcanic ash at Laetoli, Tanzania, dated to 3.66 million years ago, directly record adults and children of the same species walking side by side. Lucy may not be our direct ancestor, but she is a very close relative — and the emblem of the moment when our lineage stood up.