Madrid - More than a million years ago, a group of early humans lived in a cave in a lush green area in northern Spain, making stone tools and eating small herbivores and other animals. Their presence in what is now the fossil site of Atapuerca near Burgos has become known thanks to the discovery of a lower jaw bone with teeth, lithic tools and animal remains.
The bone, whose small size indicates that it belonged to a female, is regarded as a key piece in the puzzle that scientists are trying to put together on how the human species spread out from Africa, and on how it occupied Europe.
The bone, which was described by the journal Nature on Thursday, is hundreds of thousands of years older than the oldest direct human remains known in Western Europe so far.
The discovery indicates that hominins - a name for modern humans, their ancestors and relatives - arrived in Europe considerably earlier than had been thought, and that they may have come in from Asia.
The evidence also suggests that several human species may have evolved in Europe, painting a more complex picture of human evolution than scientists had given so far.
The Spanish discoverers of the jaw bone presented a new theory on Thursday, saying that the species that the bone corresponded to, known as Homo antecessor, was "the best candidate" to be "the direct ancestor" of modern man.
The Atapuerca complex of limestone caves has yielded abundant evidence of early human presence. Discoveries made in 1994 prompted scientists to postulate the existence of a species unknown until then, which they named Homo antecessor, Pioneer man.
The oldest Homo antecessor fossils found before the jaw bone had been about 800,000 years old.
The bone, which is up to 1.4 million years old, was found in sediments near crude stone tools and animal bones showing cut marks.
"Nobody had expected such old (human) remains to be found in Europe," Juan Luis Arsuaga, co-director of the Atapuerca excavations, told the daily El Pais.
The discovery indicates that hominins settled in Europe earlier and faster than had been thought, not long after the human species emerged from Africa.
The bone has some similarities with still older fossils from Georgia, suggesting that hominins may have entered Europe from the east rather than over other routes, such as directly from Africa over the Strait of Gibraltar.
It has been held that hominins spread out from Africa to different continents in successive waves, until the ancestors of Homo sapiens - modern humans - wiped out the earlier species.
"Until now it was believed that Europe's only contribution to human evolution were the Neanderthals," an intelligent but now extinct species, Arsuaga explains.
Comparisons between the Atapuerca and Georgian fossils, however, suggest that hominins coming from the east may have evolved into Homo antecessor in Europe.
Homo antecessor may not have been an evolutionary dead end. Spanish scientists are considering the possibility that it evolved into the Neanderthals, though there is no clear evidence of the link.
The Homo antecessor may also have mingled with newcomers from Africa, branching out into an extension of the Homo sapiens lineage, which has usually been regarded as a purely African product so far.
Human evolution does not happen in a straight line, Arsuaga stressed Thursday, presenting Homo antecessor as the likely direct ancestor of modern man.
Such theories could be confirmed or discarded as new evidence emerges.
"I am sure that within 30 or 40 years, the European evolutionary tree will be complete," Arsuaga's co-director Eudald Carbonell said.
