English: An endocast of the Australopithecus afarensis brain on display in the Hall of Human Origins in the Smithsonian Museum of Natural History in Washington, D.C.

An endocast is where scientists fill the inside of a skull, and make a model of the brain. The brain and its blood vessels leave imprints on the inside of the skull. Because more advanced brains have smaller veins and many more folds and lobes, an endocast is very useful in determing how intelligent a human ancestor might have been, and what portions of its brain were more developed.

Australopithecus afarensis is an extinct human ancestor that lived between 3.9 to 2.9 million years ago. Australopithecus afarensis was discovered in the Afar region of Ethiopia (hence the name "afarensis") in November 1973. The genus name, "Australopithecus", comes from the Latin word australis (or "southern") and the Greek word pithekos ("ape").