Oldest pre-human revealed
October 1, 2009 | David Perlman, Chronicle Science Editor
--------------------------------------------------------------------------------
SAN FRANCISCO -- After 17 years of scrabbling through the rocks
and sand of Ethopia's remote Afar deserts, a group of international
scientists has recovered the partial skeleton of an extraordinary pre-
human creature who lived in an area of East Africa 4.4 million years
ago. Her bones were found in a trove of fossils just as old, revealing the
earliest known stage in the long drama of human evolution.
over countless millennia.
The first of Ardi's bones was unearthed in 1992, and the international
team began hunting more fossils and seeking more evidence of her
ancient environment - a search that proved remarkably successful.
Piecing Ardi together
From among the bone fragments, dated at 4.4 million years ago from
the desert strata where they lay, the scientists pieced together and
identified Ardi from only 125 specimens. The partial skeleton, they
determined, was that of a 110-pound female less than four feet tall,
whose foot bones showed she walked upright but was flatfooted.
Ardi was unlike her knuckle-walking relatives, the chimpanzees, but her
hand bones, with their large, extended opposable thumbs, showed she
had retained from her ape-like ancestry an ability to climb and swing
among the trees with ease.
She and her kind are at least a million years older and show more ape-
like features than "Lucy," the famed and widely exhibited partial
hominid skeleton who lived some 3.2 million years ago.
Lucy was discovered in 1974 by Donald Johanson at Hadar, only 45
miles north of Ardi's discovery site, and identified as a new species to
be named Australopithecus afarensis.
The roadless desert site, where White and his co-leader, Berhane Asfaw
of the Rift Valley Research Service in Ethiopia, have been working with
their colleagues, lies near the tiny village of Aramis in the Awash river
region, about 140 miles northeast of Addis Ababa, the Ethiopian capital.
The discovery of the first Ardi fossils in 1992 launched the unique
series of international expeditions that have followed.
The new findings and analyses, reported in 11 separate papers by a total
of 47 authors from around the world, are being published today in a
special edition of the journal Science.
David Pilbeam, a noted Harvard anthropologist who was not connected
with the research teams, told The Chronicle that the discoveries were
"one of the most important discoveries for human evolution."
"The find itself is extraordinary, as were the enormous labors that went
into the reconstruction of a skeleton shattered almost beyond repair," he
said.
Ardi's surroundings
During interviews in his Berkeley laboratory last week, White reflected
on the discoveries.
"Think of being in a time machine," he said, "and pausing to look
around when you get to 4.4 million years ago. Out in the distance, away
from Ardi, you'd see spiral-horned antelope and other grazers feeding in
the open grassland of the savannah. But here, where Ardi and her
kinfolk are living, you'd find a fertile woodland with fruit trees and
flowers, insects, birds of all kinds and animals of all sizes - from
shrews to monkeys to elephants.
"If you went back further in time, you'd come to the big mystery -
maybe six or seven million years ago - when the Last Common
Ancestor of all the humans and all the chimpanzees must have lived -
the ancestor for which we still have found no evidence."
As he spoke, White held the original plaster skull assembled from Ardi's
skull fragments. Ardi's skull, he said, is remarkable in many ways, not
least because of its teeth. The pre-molar canine teeth in Ardi's mouth
are relatively small and blunt, much like the canines of modern humans.
So are the male canines among Ardi's group. In male chimps and other
modern apes, the canines are long and sharp and built for aggressive
slashing, White explained.
Theory on pair-bonding
In one of the Science papers published today, Owen C. Lovejoy a
renowned biological anthropologist at Kent State University argues that
Ardi's teeth offer strong evidence that the Ardipithecus tribe had already
evolved to become pair-bonded.
"This is absolutely central to human evolution," Lovejoy said in a phone
interview this week. "Over many centuries, the females would have
selected males that didn't use their canines for aggression, and the
males became aware that without attacking females they could obtain
sex for food. So the fierce canines of the males changed and they
became providers instead of aggressors, and the females could nest and
care for young."
Lovejoy's view is controversial and Pilbeam said he finds the evidence
for it "unpersuasive." But Lovejoy pointed out that where in chimps and
gorillas the males are usually much taller than the females, Ardi's small
stature and the bones of her community's males are also closer in size -
the way most humans are today. That makes it much more likely, he
said, that Ardi and her relatives lived as pairs rather than in groups of
females who mated with the most aggressive of the males.
Ardi's full name, Ardipithecus ramidus uses traditional Greek suffixes
but precedes them with words in the local Afar language: Ardi means
"ground" and ramid means "root,"so together her name literally means
"root of the ground ape."
The scientists describing their discoveries over many expeditions said
they found fossil specimens from 36 individual members of Ardi's
species, along with 29 species of birds - mostly small ones like doves,
lovebirds and swifts - and many small mammals including shrew, bats,
hares and small carnivores plus baboons and monkeys.
Among the major authors of the many reports, aside from White,
Asfaw and Lovejoy, are Giday WoldeGabrielvof the Los Alamos
National Laboratory and Gen Suwa of the University of Tokyo. Paul
Renne of the Berkeley Geochronology Center established the dates of
the rocks in the strata where the fossils were found.
E-mail David Perlman at dperlman@sfchronicle.com.
Courtesy
October 1, 2009 | David Perlman, Chronicle Science Editor
--------------------------------------------------------------------------------
SAN FRANCISCO -- After 17 years of scrabbling through the rocks
and sand of Ethopia's remote Afar deserts, a group of international
scientists has recovered the partial skeleton of an extraordinary pre-
human creature who lived in an area of East Africa 4.4 million years
ago. Her bones were found in a trove of fossils just as old, revealing the
earliest known stage in the long drama of human evolution.
- The team, led by UC Berkeley
anthropologist Tim D. White, has
assembled the female skeleton and
collected the bones of many others
from among 150,000 fossils of
animals and plants that lived among
those forebears of the human lineage
known as hominids.
The scientists had already
determined from the first few bones
they found that she was an entirely
new member of the hominid line,
and they named her Ardipithecus
ramidus, nicknamed "Ardi."
Her habitat, the project's scientists
said, was a cool and verdant spring-
fed woodland shaded by palms and
fig trees. It was uplifted later by
over countless millennia.
The first of Ardi's bones was unearthed in 1992, and the international
team began hunting more fossils and seeking more evidence of her
ancient environment - a search that proved remarkably successful.
Piecing Ardi together
From among the bone fragments, dated at 4.4 million years ago from
the desert strata where they lay, the scientists pieced together and
identified Ardi from only 125 specimens. The partial skeleton, they
determined, was that of a 110-pound female less than four feet tall,
whose foot bones showed she walked upright but was flatfooted.
Ardi was unlike her knuckle-walking relatives, the chimpanzees, but her
hand bones, with their large, extended opposable thumbs, showed she
had retained from her ape-like ancestry an ability to climb and swing
among the trees with ease.
She and her kind are at least a million years older and show more ape-
like features than "Lucy," the famed and widely exhibited partial
hominid skeleton who lived some 3.2 million years ago.
Lucy was discovered in 1974 by Donald Johanson at Hadar, only 45
miles north of Ardi's discovery site, and identified as a new species to
be named Australopithecus afarensis.
The roadless desert site, where White and his co-leader, Berhane Asfaw
of the Rift Valley Research Service in Ethiopia, have been working with
their colleagues, lies near the tiny village of Aramis in the Awash river
region, about 140 miles northeast of Addis Ababa, the Ethiopian capital.
The discovery of the first Ardi fossils in 1992 launched the unique
series of international expeditions that have followed.
The new findings and analyses, reported in 11 separate papers by a total
of 47 authors from around the world, are being published today in a
special edition of the journal Science.
David Pilbeam, a noted Harvard anthropologist who was not connected
with the research teams, told The Chronicle that the discoveries were
"one of the most important discoveries for human evolution."
"The find itself is extraordinary, as were the enormous labors that went
into the reconstruction of a skeleton shattered almost beyond repair," he
said.
Ardi's surroundings
During interviews in his Berkeley laboratory last week, White reflected
on the discoveries.
"Think of being in a time machine," he said, "and pausing to look
around when you get to 4.4 million years ago. Out in the distance, away
from Ardi, you'd see spiral-horned antelope and other grazers feeding in
the open grassland of the savannah. But here, where Ardi and her
kinfolk are living, you'd find a fertile woodland with fruit trees and
flowers, insects, birds of all kinds and animals of all sizes - from
shrews to monkeys to elephants.
"If you went back further in time, you'd come to the big mystery -
maybe six or seven million years ago - when the Last Common
Ancestor of all the humans and all the chimpanzees must have lived -
the ancestor for which we still have found no evidence."
As he spoke, White held the original plaster skull assembled from Ardi's
skull fragments. Ardi's skull, he said, is remarkable in many ways, not
least because of its teeth. The pre-molar canine teeth in Ardi's mouth
are relatively small and blunt, much like the canines of modern humans.
So are the male canines among Ardi's group. In male chimps and other
modern apes, the canines are long and sharp and built for aggressive
slashing, White explained.
Theory on pair-bonding
In one of the Science papers published today, Owen C. Lovejoy a
renowned biological anthropologist at Kent State University argues that
Ardi's teeth offer strong evidence that the Ardipithecus tribe had already
evolved to become pair-bonded.
"This is absolutely central to human evolution," Lovejoy said in a phone
interview this week. "Over many centuries, the females would have
selected males that didn't use their canines for aggression, and the
males became aware that without attacking females they could obtain
sex for food. So the fierce canines of the males changed and they
became providers instead of aggressors, and the females could nest and
care for young."
Lovejoy's view is controversial and Pilbeam said he finds the evidence
for it "unpersuasive." But Lovejoy pointed out that where in chimps and
gorillas the males are usually much taller than the females, Ardi's small
stature and the bones of her community's males are also closer in size -
the way most humans are today. That makes it much more likely, he
said, that Ardi and her relatives lived as pairs rather than in groups of
females who mated with the most aggressive of the males.
Ardi's full name, Ardipithecus ramidus uses traditional Greek suffixes
but precedes them with words in the local Afar language: Ardi means
"ground" and ramid means "root,"so together her name literally means
"root of the ground ape."
The scientists describing their discoveries over many expeditions said
they found fossil specimens from 36 individual members of Ardi's
species, along with 29 species of birds - mostly small ones like doves,
lovebirds and swifts - and many small mammals including shrew, bats,
hares and small carnivores plus baboons and monkeys.
Among the major authors of the many reports, aside from White,
Asfaw and Lovejoy, are Giday WoldeGabrielvof the Los Alamos
National Laboratory and Gen Suwa of the University of Tokyo. Paul
Renne of the Berkeley Geochronology Center established the dates of
the rocks in the strata where the fossils were found.
E-mail David Perlman at dperlman@sfchronicle.com.
Courtesy
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