The Sterkfontein Caves, a network of limestone caverns northwest of Johannesburg, South Africa, offer a window into the deep past of our species. This location has yielded a large collection of early human ancestor fossils. The discoveries have shaped our understanding of human origins, providing evidence of the ancient hominins that once roamed southern Africa.
The History of Discovery
The scientific history of Sterkfontein began as a byproduct of industry. In the late 1890s, lime miners blasted the caves to extract calcite flowstones for processing gold from the nearby Witwatersrand reefs. This quarrying exposed fossil-rich, cement-like breccia deposits that had sealed ancient remains for millions of years. For decades, these fossils were largely discarded.
The site’s potential was recognized in the 1930s. Following the 1924 discovery of the Taung Child, paleontologist Dr. Robert Broom became interested in the region. In 1936, a tip from his students who had found fossil baboon skulls led Broom to the Sterkfontein limeworks. His inquiries led to the discovery of an adult Australopithecus fossil, launching a new era of paleontological excavation at the caves.
Significant Fossil Finds
Sterkfontein has produced more than a third of all early hominin fossils ever found. Among the hundreds of specimens, two are notable for their completeness. The first is “Mrs. Ples,” a well-preserved cranium of an Australopithecus africanus discovered by Robert Broom and John T. Robinson in 1947. This fossil provided the first evidence of an adult of the same species as the juvenile Taung Child.
Another discovery is “Little Foot” (StW 573), an almost complete skeleton of an Australopithecus. Its foot bones were identified by paleoanthropologist Ronald J. Clarke in 1995 among fossils in storage. This began a painstaking, two-decade-long excavation to free the rest of the skeleton from the rock of the Silberberg Grotto. The result is a fossil whose completeness offers insights into anatomy and locomotion beyond what a single skull or jawbone can provide.
The collection includes the remains of over 500 hominins. These represent not just Australopithecus, but also early members of our genus, Homo, and another hominin branch, Paranthropus. This concentration of fossils allows scientists to study variation within a population, providing a better picture of these ancient species than isolated finds could.
The Evolutionary Significance
The fossils of Sterkfontein provide a snapshot of a time in human evolution. The anatomy of Australopithecus africanus, revealed by finds like Mrs. Ples and Little Foot, shows a mosaic of traits. These hominins were adapted for bipedalism (walking on two legs), a feature of the human lineage. They also retained ape-like characteristics like long arms and curved fingers, suggesting they were adept climbers.
This combination of features helps scientists reconstruct the behavior of these early ancestors in a mixed woodland and savanna environment. The fossils allow for biomechanical studies that inform our understanding of how upright walking evolved. These ancient relatives were a successful species in their own right for an extensive period.
The dating of these fossils has been a source of scientific investigation. Recent analyses using cosmogenic nuclide dating have challenged previous estimates by measuring radioactive decay in the surrounding quartz. This method has pushed the age of the Member 4 deposit, where Mrs. Ples was found, to between 3.4 and 3.6 million years old. This revised timeline suggests Australopithecus africanus may be a contemporary of other early hominin species rather than a direct ancestor of Homo.
Visiting the Cradle of Humankind
The Cradle of Humankind UNESCO World Heritage Site offers an accessible experience for those interested in this history. The journey can begin at the Maropeng Visitor Centre, an exhibition space a short drive from the caves. Maropeng features interactive displays about human evolution and the formation of our planet. It provides context for the discoveries made at the nearby fossil sites.
The tour of the Sterkfontein Caves offers a glimpse into the world of paleontologists. Visitors are guided into the limestone caverns, passing excavation sites where discoveries were made. The original fossils are housed at the University of the Witwatersrand for research, but the tour showcases the geological setting and the conditions under which scientists work. This connects the public to the source of these discoveries.