Klasies river mouth site dating Porncha
The results of the find will be reported in two papers in the June 12 issue of the journal Nature.
"In a sense, these genetic findings were impossible to seriously test without a good fossil record from Africa," said White.
The most complete of the three new fossil skulls, probably that of a male, is slightly larger than the extremes seen in modern Homo sapiens, yet it bears other characteristics within the range of modern humans - in particular, less prominent brow ridges than pre-Homo sapiens and a higher cranial vault.
Because of these similarities, the researchers placed the fossils in the same genus and species as modern humans but appended a subspecies name - Homo sapiens idaltu -to differentiate them from contemporary humans, Homo sapiens sapiens.
The fossils date precisely from the time when biologists using genes to chart human evolution predicted that a genetic "Eve" lived somewhere in Africa and gave rise to all modern humans.
"We've lacked intermediate fossils between pre-humans and modern humans, between 100,000 and 300,000 years ago, and that's where the Herto fossils fit," said paleoanthropologist Tim White, professor of integrative biology at the University of California, Berkeley, and a co-leader of the team that excavated and analyzed the discovery site.
When the team returned to intensively survey the area 11 days later, they discovered the most complete of the adult skulls protruding from the ancient sediment.