Perhaps the best known of all early hominids, Lucy lived in eastern Africa more than three million years ago. Members of her species were among the early human ancestors to venture down from the trees and into the grassy woodlands along the edges of forests—a move made possible in part because the hominids of this era could walk on two limbs instead of four. The ability to walk upright emerged over four million years ago and was probably the fundamental innovation on which all later hominid evolution was based.

Lucy ©AMNH

The researchers who discovered this skeleton in Hadar, Ethiopia, in 1974 recovered only fragments. Nevertheless, this specimen, nicknamed Lucy, is the most complete skeleton found to date from the diverse group of early hominids that flourished between two and seven million years ago.

The Lucy skeleton is 3.18 million years old and consists of bones from a single individual, presumably female, who stood well under four feet tall. Her long arms, narrow shoulders and short legs are typical of a tree-dwelling hominid.

Lucy belongs to the species Australopithecus afarensis and is often described as a bipedal ape. Analysis of the pelvis, thigh bone and knee joint indicate that Lucy and her kind walked on two feet, making them bipeds. But their small brains and large, protruding faces resembled those of apes.

Although these bipedal apes probably spent much of their time in trees, searching for food and refuge from predators, they also walked upright across the open savanna, where they might have found food such as roots or tubers or the remains of animals to scavenge for meat.