French and Kenyan scientists have unearthed fossilised remains of mankind's earliest known ancestor that predate previous discoveries by more than 1.5 million years, the team announced yesterday.
They said the discovery of Millennium Man, as the creature has been nicknamed, could change the way scientists think about evolution and the origin of species.
The first remains were discovered in the Tugen hills of Kenya's Baringo district on October 25th by a team from College de France in Paris and the Community Museums of Kenya.
Since then the scientists have unearthed distinct body parts belonging to at least five individuals, both male and female.
"Not only is this find older than any other previously known, it is also in a more advanced stage of evolution," a palaeontologist, Mr Martin Pickford, told a news conference. "It is at least six million years old, which means it is older than the [previously oldest] remains found at Aramis in Ethiopia, which were 4.5 million years old."
"Lucy", the skeleton of Australopithicus afarensis found in Ethiopia in 1974, is believed to have lived around 3.2 million years ago.
An almost perfectly fossilised left femur shows the much older Millennium Man already had strong back legs which enabled it to walk upright - giving it hominid characteristics which relate it directly to man.
A thick right humerus bone from the upper arm suggests it also had tree-climbing skills, but probably not enough to "hang" from tree branches or swing limb to limb.
The length of the bones shows the creature was about the size of a modern chimpanzee, according to Ms Brigitte Senut, a team member from the Museum of Natural History in Paris.
But it is the teeth and jaw structure which most clearly links Millennium Man to the modern human. It has small canines and full molars - similar dentition to modern man and suggesting a diet of mainly fruit and vegetables with occasional opportunistic meat-eating.
The Baringo area is part of Africa's Great Rift Valley, which has long been rich in archaeological and palaeontological discoveries and the source of almost all fossils related to man's earliest ancestors.
The area where the remains were found is home to Kenya's long-serving President Daniel arap Moi.