Australopithecus afarensis is an extinct species of hominid that lived between 3.9 and 2.9 million years ago in East Africa. This species is known for its bipedal locomotion and is considered a crucial link in human evolution. One of the most famous specimens, Lucy, was discovered in 1974 and provided significant insights into the physical characteristics and behaviors of early hominids. Australopithecus afarensis had a small brain size, similar to that of modern chimpanzees, but exhibited a combination of ape-like and human-like traits. Its ability to walk upright suggests adaptations to both arboreal and terrestrial environments, highlighting the evolutionary transition from tree-dwelling ancestors to ground-dwelling humans.