The Evolutionary History of the Australopiths

The australopiths are a group of early hominins (humans and their close extinct relatives) that lived in Africa between approximately 4.1 and 1.4 million years ago. Formerly known as the australopithecines, they are not a “natural” group, in that they do not represent all of the descendants of a single common ancestor (i.e., they are not a “clade”). Rather, they are grouped together informally because nearly all share a similar adaptive grade (i.e., they have similar adaptations). In particular, they are bipedal apes that, to a greater or lesser extent, exhibit enlarged molar and premolar teeth (postcanine megadontia) and other associated modifications to their feeding apparatuses. Dietary adaptations clearly played an important role in shaping their evolutionary history. They also are distinguished by their lack of derived features typically associated with the genus Homo, such as a large brain, a broad complement of adaptations for manual dexterity, and advanced tool use. However, Homo is almost certainly descended from an australopith ancestor, so at least one or some australopiths belong directly to the human lineage. Regardless, australopiths had a rich evolutionary history deserving of study independent of questions about our direct ancestry. They were diverse, geographically widespread, and anatomically derived, they lived through periods of pronounced climate change, and their story dominates the narrative of human evolution for millions of years.