For paleoanthropologists, the birth of our genus has long been a conundrum, with only a few scattered and fragmentary fossils older than two million years have been argued to belong to the genus.
Now, the fossil remains found in a cave in South Africa in April 2010 could represent an evolutionary link between apes and our earliest human ancestors.
Lee Berger, a paleoanthropologist at the University of the Witwatersrand, and his colleagues believe the almost-complete fossilised skeleton belonged to an intermediate form between the primitive australopiths and our genus, Homo.
The fossils of a female adult and a juvenile male - perhaps 12 or 13 years old - were uncovered in an eroded limestone cave at Malapa, about 25 miles northwest of Johannesburg.
The site is in a region already so famous for its ancient human fossils that it is often referred to as the 'Cradle of Humankind'.
Berger believes Malapa may hold the key to one of the most significant, least understood chapters in the human evolutionary journey: the origin of the first species enough like us to be called human-a member of the genus Homo.
"This is where that story may have begun," National Geographic News quoted him as saying.
The fossils included an australopith's little brain (with some curiously modern features), apelike shoulders, and arms adapted to climbing in trees-attached to a bizarrely modern hand with the precision grip of a toolmaker.
According to the researchers, the adult female's foot presents an even odder melange; her mostly modern ankle is connected to a heel bone more primitive than that of A. afarensis-Lucy's species-which is at least a million years older.
"It really is a jaw-dropping find," said Carol Ward, a paleoanthropologist at the University of Missouri who studies the evolution of apes and early hominins (a term for humans and other nonape primates; some researchers prefer the older term, hominid).
"We have no other collection of fossil skeletons, until the Neanderthals just over 100,000 years ago, that are so articulated, so complete," added Ward.