That's the conclusion of a battery of studies carried out on two strange skeletons discovered near Johannesburg in 2008. They represent a likely stepping stone between the ape-like australopiths and the first members of our own genus.

The origins of the species remain surprisingly obscure. But the two skeletons, unusually, suggest our ancestor may have climbed back up into the trees – after having evolved to walk on the ground.

It was around 2 million years ago that the first humans evolved from smaller-brained australopiths. The precise species that gave rise to humanity has never been found, but it seems that Australopithecus sediba, discovered in 2008, was very closely related to it.

A new set of studies, published in Science, confirm that A. sediba carried a bizarre mosaic of ancient australopith and modern Homo features – making it possible that the fossils are an "ideal ancestral form of the genus Homo", says Peter Schmid at the University of Zurich, Switzerland.