Fossilised remains belonging to some of humanity's oldest ancestors are approximately one million years older than scientists had previously thought, new research suggests.
The fossils, including one belonging to ancient cave woman Mrs Ples, were buried for millennia in South African caves.
The latest testing methods now indicate the group of early humans roamed the earth between 3.4 and 3.7 million years ago.
This new timeline could lead to a revaluation of our comprehension of human evolution. It opens up more possible paths by which our ancestors could have evolved into early humans.
Scientists long believed the Australopithecus africanus species, whose fossils were discovered in the Sterkfontein caves near Johannesburg, had been less than 2.6 million years old.
The underground complex, known as the “Cradle of Humankind”, has presented more early human remains than anywhere else in the world - including the near complete skull discovered in 1947 belonging to an early cave woman nicknamed Mrs Ples.
According to the Smithsonian Museum, the species - which walked on two feet - were much shorter than modern-day humans. Males were an average of 138cm (4ft 6in) in height and females averaged 115cm (3ft 9in).
Researchers tested sediment around the fossils for levels of a rare isotope created when the rocks were exposed to cosmic rays and subsequently revised the previous estimate. The lead author of the study, Darryl Granger of Purdue University in the US stated: “Their radioactive decay dates when the rocks were buried in the cave when they fell in the entrance together with the fossils.”
Previously, the Australopithecus africanus hominids were considered by scientists to be too young to have evolved into the homo genus, our ancestors, who roamed earth around 2.2 million years ago.
These findings now suggest they had one million additional years to make that evolutionary leap - making it a possibility that Mrs Ples, and the species she was part of, were ancestors of early humans.
The new timeline hints at possible interaction and breeding between the two species, scientists say. Consequently the pre-existing notion of where humans came from and it being a straightforward evolutionary line may require revision.
French scientist Laurent Bruxelles and member of the study team said it means our family tree is in fact “more like a bush.”