A section of the Sterkfontein Caves has been found to be more than a million years older than previously thought -- a discovery that is likely to shake up our family tree.

The part of Sterkfontein Caves that lies 40km northwest of Johannesburg is known as Member 4 and it contains the richest deposit of Australopithecine fossils in the world.

More than 500 of these ancestors that belong to a family of hominids from an ancient branch of the human family tree have been found in the cave, but their being there is a decades-old mystery. The Australopithecus fossils found here were younger than their counterparts in East Africa, and this didn't fit into our understanding of hominid evolution.

Scientists have for decades puzzled over the age of Member 4. Initially, it was thought that Member 4 was just over two million years old, making all those fossils found there that age too.

"It just didn't make sense," says Professor Dominic Stratford, director of research at the caves, and one of the authors of the paper that appeared in the journal Proceedings of the National Academy of Sciences.

Fossils now tie up with those in East Africa

Now, through the...