'First human' discovered in Ethiopia
The 2.8 million-year-old specimen is 400,000
years older than researchers thought that our
kind first emerged.
The discovery in Ethiopia suggests climate
change spurred the transition from tree
dweller to upright walker.
The head of the research team told BBC
News that the find gives the first insight into
"the most important transitions in human
evolution".
Prof Brian Villmoare of the University of
Nevada in Las Vegas said the discovery makes
a clear link between an iconic 3.2 million-
year-old hominin (human-like primate)
discovered in the same area in 1974, called
"Lucy".
Could Lucy's kind - which belonged to the
species Australopithecus afarensis - have
evolved into the very first primitive humans?
"That's what we are arguing," said Prof
Villmoare.
But the fossil record between the time period
when Lucy and her kin were alive and the
emergence of Homo erectus (with its
relatively large brain and humanlike body
proportions) two million years ago is sparse.
The 2.8 million-year-old lower jawbone was
found in the Ledi-Geraru research area, Afar
Regional State, by Ethiopian student
Chalachew Seyoum. He told BBC News that
he was "stunned" when he saw the fossil.
"The moment I found it, I realised that it was
important, as this is the time period
represented by few (human) fossils in Eastern
Africa."
The fossil is of the left side of the lower jaw,
along with five teeth. The back molar teeth
are smaller than those of other hominins
living in the area and are one of the features
that distinguish humans from more primitive
ancestors, according to Professor William
Kimbel, director of Arizona State University's
Institute of Human Origins.
"Previously, the oldest fossil attributed to the
genus Homo was an upper jaw from Hadar,
Ethiopia, dated to 2.35m years ago," he told
BBC News.
"So this new discovery pushes the human line
back by 400,000 years or so, very close to its
likely (pre-human) ancestor. Its mix of
primitive and advanced features makes the
Ledi jaw a good transitional form between
(Lucy) and later humans."
A computer reconstruction of a skull
belonging to the species Homo habilis,
which has been published in Nature journal,
indicates that it may well have been the
evolutionary descendant of the species
announced today.
The researcher involved, Prof Fred Spoor of
University College London told BBC News
that, taken together, the new findings had
lifted a veil on a key period in the evolution of
our species.
"By discovering a new fossil and re-analysing
an old one we have truly contributed to our
knowledge of our own evolutionary period,
stretching over a million years that had been
shrouded in mystery," he said.
Climate change
The dating of the jawbone might help answer
one of the key questions in human evolution.
What caused some primitive ancestors to
climb down from the trees and make their
homes on the ground.
A separate study in Science hints that a
change in climate might have been a factor.
An analysis of the fossilised plant and animal
life in the area suggests that what had once
been lush forest had become dry grassland.
As the trees made way for vast plains,
ancient human-like primates found a way of
exploiting the new environmental niche,
developing bigger brains and becoming less
reliant on having big jaws and teeth by using
tools.
Prof Chris Stringer of the Natural History
Museum in London described the discovery as
a "big story".
He says the new species clearly does show
the earliest step toward human
characteristics, but suggests that half a
jawbone is not enough to tell just how human
it was and does not provide enough evidence
to suggest that it was this line that led to us.
The jawbone was found close to the area
where Lucy was discovered
He notes that the emergence of human-like
characteristics was not unique to Ethiopia.
"The human-like features shown by
Australopithecus sediba in South Africa at
around 1.95 million years ago are likely to
have developed independently of the
processes which produced (humans) in East
Africa, showing that parallel origins are a
distinct possibility," Prof Stringer explained.
This would suggest several different species
of humans co-existing in Africa around two
million years ago with only one of them
surviving and eventually evolving into our
species, Homo sapiens. It is as if nature was
experimenting with different versions of the
same evolutionary configuration until one
succeeded.
Prof Stringer added: "These new studies
leave us with an even more complex picture
of early humans than we thought, and they
challenge us to consider the very definition of
what it is to be human. Are we defined by our
small teeth and jaws, our large brain, our
long legs, tool-making, or some combination
of these traits?"
