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SUNDAY SCIENCE: LUCY’S WORLD  
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Ann Gibbons
April 5, 2024
Science
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_ Fifty years after her discovery, the 3.2-million-year-old fossil
still reigns as mother of us all. But she now has rivals _

Lucy’s iconic partial skeleton, 40% complete, was discovered at
Hadar in Ethiopia in 1974., Bruce Frumker

 

Zeresenay Alemseged doesn’t remember the 1974 discovery of the
famous fossil Lucy at Hadar in Ethiopia, because he was 5 years old,
living 600 kilometers away in Axum. Later he saw Lucy’s name on
cafes and taxis, but he knew little about her until he became a
geologist working at the National Museum of Ethiopia. Then, she
changed his life.

In 2000, Alemseged was swept into Lucy’s orbit: He discovered
“Lucy’s child,” a partial skeleton of a toddler of her species,
at Dikika, 10 kilometers from Hadar. In 2015, by then a well-known
scientist, he had the honor of showing Lucy to then-President Barack
Obama before a state dinner at Ethiopia’s National Palace. Alemseged
allowed Obama to touch the prized skeleton, telling him the fossil
shows Ethiopia is the birthplace of humankind and that “every single
person” on the planet shares an origin in Africa. “Including
Donald Trump,” Alemseged joked to Obama.

Fifty years after her discovery, “Lucy is an icon,” says
Alemseged, now a paleoanthropologist at the University of Chicago.

Indeed, the 3.18-million-year-old has reigned as the matriarch of the
human family ever since she was announced as the earliest known
ancestor of our genus, _Homo_, as well as of all other hominins that
came after her. Heads of state paid court to her. Scores of Texans
lined up to see her in 2006 when she made a U.S. tour, which was
controversial because many scientists thought she was too fragile to
travel. Even Ivanka Trump got an audience. But like many aging
monarchs, Lucy now faces a new world, rife with competition for
attention and status from her extended family.

Five decades of research have brought Lucy to life, showing how she
walked upright even though she still had a small brain and apelike
upper body, which probably allowed her to climb trees to feed, nest,
or escape predators. More than 400 newer fossils of males and females,
as well as the Dikika child, have revealed how her
species, _Australopithecus afarensis_, grew, socialized, and evolved
during its million-year span on the planet, from perhaps 3.85 million
to 2.95 million years ago.

But researchers’ view of Lucy’s world and her place in it has
changed. She is no longer the earliest known member of the human
family. Members of her species didn’t take their first upright steps
in open savanna grasslands, as her discoverers thought, but walked
first in a grassy woodland with deciduous trees. She and her kind
weathered climate change, adapting to different habitats over the
millennia. Most important, she wasn’t alone in the landscape. “We
have multiple [hominin] species in the same time period,” says
Yohannes Haile-Selassie, director of the Institute of Human Origins
(IHO) at Arizona State University, who is coorganizing a symposium
this week on Lucy’s impact on human origins research.

Haile-Selassie and some others think that 3 million to 4 million years
ago, the human family tree was more like a bush than a bonsai, with
multiple stems growing side by side rather than a single trunk. He and
others now see Lucy as more of a great-great-great-aunt than a direct
human ancestor. But Alemseged and others point out that so far, no
other fossil is a better candidate for being the mother of us all.

Even as paleoanthropologists debate her place in the human family
tree, they agree no known human ancestor has had the impact of Lucy.
They still marvel at the detailed view of our past revealed by her
skeleton. Forty percent complete, it has served as a template for
fitting together the isolated bones of dozens of other members of her
species, like pieces in an incomplete puzzle. “More people have come
to look and analyze Lucy’s skeleton than any other fossil in the
world,” says IHO paleoanthropologist Kaye Reed.

Back in 1974, researchers didn’t realize just how rare such a
well-preserved hominin skeleton would turn out to be. “Fate played a
miserable trick—it gave us the best fossil early on,” says
paleoanthropologist Bernard Wood of George Washington University.
“It’s as if it’s my birthday and I’ve opened my first present
and it’s exactly what I want … so you think that all the other
presents will be as good as this one.”

THAT FOSSIL GIFT of a lifetime was first unwrapped by Don Johanson.
Then a young American paleoanthropologist at the Cleveland Museum of
Natural History, he had joined an expedition at Hadar organized by
late French geologist Maurice Taieb. On 24 November 1974, halfway
through the second field season, Johanson and student Tom Gray were
walking back to their Land Rover after a discouraging morning when
they had found little of interest. Then, Johanson saw a bit of
Lucy’s arm bone on a hill in a dry gully. Next he spotted a skull
piece, a thighbone, part of a pelvis, and vertebrae: a rare partial
skeleton.

The team celebrated the discovery in camp, drinking beer and blasting
the Beatles’s song _Lucy in the Sky with Diamonds_ all night.
Someone started to call the skeleton Lucy, and the name stuck.

Photo: John Gurche

LUCY THE HOMININ

AGE: 3.18 million years old

SPECIES: Australopithecus afarensis

SIZE: 1 meter tall, 30 kilograms

FAMILY: All of _Homo_ and _Australopithecus_, but it’s
complicated

HOMETOWN: Hadar in Ethiopia. Now resides at the National Museum of
Ethiopia in Addis Ababa

LIKES: Wooded grasslands, for walking upright and climbing trees to
escape predators. Enjoys figs, berries, sedge grasses

KNOWN FOR: Good bones; well-preserved skeleton includes jaw, ribs,
pelvis, and parts of arms and leg

DISCOVERED: 24 November 1974

NAMED AFTER: A Beatles song

“The real importance of Lucy is we didn’t know what an early human
ancestor looked like,” says Johanson, founder of IHO. He recalls
that he was immediately impressed by how small and primitive Lucy was
compared with known members of _Australopithecus_, such as _A.
africanus_, a hominin found in South Africa almost a century ago, and
thought at the time of Lucy’s discovery to be about 2 million years
old. “I was struck by her more apelike features,” he says.

Lucy was the first hominin to break the 3-million-year time barrier,
pushing back the age of the human family to a time closer to when
geneticists thought the ancestor of humans had split from the ancestor
of chimpanzees. Lucy “entered a field actively debating the
antiquity of the chimp/human split,” says Tim White, a
paleoanthropologist at the University of California, Berkeley who
coauthored the landmark 1978 paper describing Lucy’s species with
Johanson and the late paleoanthropologist Yves Coppens.

For the first 20 years after Lucy’s discovery, her species was the
oldest known member of the human family. _A. afarensis_ was “the
only game in town” between 3 million and 4 million years ago, says
Carol Ward, a paleoanthropologist at the University of Missouri. Many
researchers concluded that her species gave rise to all the hominins
that came later, including _Homo, A. africanus_, and more robust
members of the human family such _Paranthropus aethiopicus, P.
robustus_, and _P. boisei_.

Zeresenay Alemseged (left) showed Lucy’s jaw to then-President
Barack Obama in Addis Ababa, Ethiopia, in 2015. PHOTO: EVAN VUCCI/AP

“Once upon a time, life was relatively simple because anything
before 3 million years was _A. afarensis_ … [and] it was the
mother of us all,” says paleontologist Fred Spoor of the Natural
History Museum in London. “That was the gospel.”

Since then, however, other species have emerged from the shadows, some
of them much older. Lucy was so apelike that “the implicit
hypothesis was that the next step back would be a chimpanzee,” says
White, who found fossils and analyzed footprints of Lucy’s species
at Laetoli in Tanzania. “How quaint that seems today.”

In the mid-1990s, White, then–graduate student Haile-Selassie, and
others began an intense search for Lucy’s ancestors in the Middle
Awash region of Ethiopia. They found a remarkably complete but crushed
partial skeleton they named _Ardipithecus ramidus_, dated to 4.4
million years ago. Nearby, Haile-Selassie later found the lower jaw,
teeth, and disarticulated bones of the hands, feet, and arm
of _Ardipithecus kadabba_, dated to 5.8 million years ago. These
primitive hominins looked more like upright apes than humans. “You
wouldn’t invite [them] to dinner,” White joked. _Ardipithecus_,
he says, “makes Lucy and Co. downright humanlike in comparison.”

The day after he found Lucy in November 1974, Don Johanson studies the
exact spot where he picked up the first bone, her elbow. PHOTO: BOBBIE
BROWN

In camp, Johanson (left) and Maurice Taieb scrutinize and photograph
the spectacular find. PHOTO: INSTITUTE OF HUMAN ORIGINS

Other new fossils pushed the human lineage even older: a
6-million-year-old thighbone from an apparent upright walker from
Kenya called Millennium Man, or _Orrorin tugenensis_; and a stunning
skull of _Sahelanthropus tchadensis_, dated 6 million to 7 million
years old, from Chad.

Anthropologists still fiercely debate whether all these species are
hominins, and how they relate to _Australopithecus_, not to mention
Homo. But the fossils clearly push back the origin of the human family
to at least 6 million years ago, a date that dovetails with the most
recent genetic evidence for the timing of the split between our
lineage and that of chimps and bonobos.

Meanwhile, other researchers kept seeking fossils in the key period
about 4 million years ago—and found what seemed to be a
great-grandmother for Lucy. In 1994, Kenyan paleoanthropologist Meave
Leakey and her team found more than 80 fossils of teeth, jaws, a
partial arm, and shinbone at two sites near Lake Turkana in Kenya.
They dated the fossils to between 3.9 million and 4.2 million years
ago, and named the species _Australopithecus anamensis_. Based on
features of its teeth and jaw, they proposed the new species was the
direct ancestor of Lucy and her kin.

CREDITS: (GRAPHIC) D. AN-PHAM/SCIENCE; (DATA) U.S. GEOLOGICAL SURVEY

Then in 2016, in a hilly area just 30 kilometers from Hadar called
Woranso-Mille, Haile-Selassie made a discovery that complicated the
picture. With help from a local goat herder, he found the first
complete skull of _A. anamensis_. The stunning skull dated to 3.8
million years ago, a bit younger than the earliest fossil attributed
to Lucy’s species, a jaw dated to 3.85 million years. The notion
that _A. anamensis_ had evolved directly into Lucy’s species and
then vanished was off the table. Instead, perhaps an earlier member
of _A. anamensis_—or even another closely related species—gave
rise to _A. afarensis_, and the two lineages coexisted for a time.

Even as they sought Lucy’s ancestors, paleoanthropologists also kept
searching for her descendants, looking for a path from her genus to
our own.

IDENTIFYING THE DIRECT ANCESTOR of _Homo_ is challenging, Ward
says, in part because “we don’t know much about early _Homo_.”
The earliest known fossil of our genus is a lower jaw with worn
molars, dating to almost 2.8 million years ago and found at the
desolate site of Ledi-Geraru, only 30 kilometers from Hadar (see map,
above). “It’s a convincing case,” Ward says, “but it’s just
one mandible until about 2 million years ago,” when at least two
members of the genus, _Homo habilis_ and _H. erectus_, appear
elsewhere in eastern Africa.

The jaw’s age suggests _Homo_ made its entrance about 3 million
years ago, not long after Lucy lived. But there are new contenders to
be ancestors of _Homo_, because at that time, eastern Africa appears
to have been home to a diverse set of hominins (see graphic, p. 25).

One is known from a strange crushed skull dating to 3.5 million years
ago, which Leakey’s team found at Lomekwi on the west side of Lake
Turkana in 1999. She and Spoor painstakingly reconstructed the skull
fragments like pieces in a 3D puzzle. They concluded they had a new
species, _Kenyanthropus platyops_, with a flatter face and smaller
molars than Lucy’s species—traits suggesting it was intermediate
between Lucy and _Homo_.

With only that crushed skull, however, _Kenyanthropus_ got a mixed
reception. White called it roadkill and suggested it was a
smashed _A. afarensis_. More recently, Spoor and Leakey applied 3D
morphometric methods to compare _Kenyanthropus’s_ upper jaw with
those of a half-dozen other hominins, and convinced many researchers
to take it seriously as a separate species. Researchers identified
additional isolated teeth of the species at Lomekwi, but the species
is still poorly known.

Meanwhile, Haile-Selassie found two additional hominins at his site of
Woranso-Mille that further tangle the human family tree just
before _Homo_ appeared. One, the Burtele foot, named after the
3.4-million-yearold layer of sediment in which it was found, lived at
the same time as _A. afarensis_ but is more primitive, with an
opposable big toe like that of tree-climbing _Ardipithecus_. His team
also found teeth and two upper and two lower jaws he attributes to a
new species he named _A. deyiremeda_ that lived 3.3 million to 3.5
million years ago. When he published the discovery in 2015, reaction
was mixed; White, Alemseged, and others thought the jaws were diverse
forms of _A. afarensis_, which was found within 5 kilometers of the
site.

But Spoor and his postdoc recently backed Haile-Selassie’s claim.
They did a 3D morphometric analysis of developmental differences in
the upper jaw bones of _A. afarensis_, _A. deyiremeda_, and _K.
platyops_, highlighting the methodological advances in the field since
Lucy was found. The comparisons “demonstrate significant
differences,” Spoor argued in a talk at the College of France in
June 2023. “It confirms the status of _K. platyops_ and _A.
deyiremeda_ as valid species different from _A. afarensis_.”

Yohannes Haile-Selassie unveils a replica of the 3.9-million-year-old
skull of Australopithecus anamensis, which many think is the ancestor
of Lucy’s species. PHOTO: SETH WENIG/AP

No one is arguing that _A. deyiremeda_ is a closer ancestor to Homo
than Lucy. But the new fossils suggest a burst of diversity 3.5
million years ago, crowding the stage on which Lucy once stood alone.
She may have been part of an adaptive radiation that happened earlier
than researchers once thought, perhaps after hominins began to walk
upright and expanded their habitats and diets, Ward says.

Some of those hominins may have trod the same ground as Lucy’s
species. In 2020, paleoanthropologist Charles Musiba of the University
of Colorado Denver and his colleagues reanalyzed famous tracks
discovered in 1976 at Laetoli. Some prints are thought to be the
footprints of _A. afarensis_ about 3.7 million years ago. Other
tracks, about the same age, were believed to have been made by
animals. Musiba and his colleagues, however, proposed that the prints
were made by upright walkers—a hominin with different feet and gait
from Lucy’s species.

Lucy is a national treasure in Ethiopia, where students and others
often visit her skeleton at the National Museum of Ethiopia in Addis
Ababa. PHOTO: IMAGO/ALAMY

Meanwhile, another clue in the search for ancestors has emerged in
South Africa, where researchers have discovered other early members
of _Australopithecus_, such as _A. sediba_, dating to about 2
million years ago and possibly earlier. A new analysis in
the _Journal of Human Evolution_ last year could not rule out
that _A. sediba_ shared an ancestor that also gave rise to
early _Homo_, raising the possibility that our ancestor ranged from
eastern Africa to South Africa.

At the moment, none of the new hominins is convincing as a direct
forebear of _Homo_. Alemseged and some others still put their money
on Lucy: They point out that no fossils unequivocally bump her species
from its prime spot as the putative ancestor of early _Homo_ and
later members of _Australopithecus_.

Others say we just don’t know. “It’s too simplistic to create
ancestor-descendants out of currently known species from an incomplete
fossil record,” Spoor says. Given the rarity of fossilization for
hominin remains and how few have been found, we might never catch a
glimpse of our immediate direct ancestor, Wood says. It’s unlikely
that “all the hominins that ever lived occupied the circa 1% of the
land surface of Africa where we happen to find fossils,” he says.

LUCY’S STATUS as a human ancestor may be uncertain, but in other
ways she is coming into sharper focus. “When Lucy was found, we
thought _Homo habilis_ was the one who made the earliest tools,”
says archaeologist Sonia Harmand of the French national research
agency CNRS. But at Lomekwi, where _Kenyanthropus_ was found,
Harmand and her team unearthed crude stone tools from 3.3 million
years ago, early enough for either _Kenyanthropus_ or
an _Australopithecus_ to have hafted them. Lucy’s brain was only a
bit bigger than an ape’s relative to her body size, but her hand and
that of other members of _Australopithecus_ was probably capable of
smashing bones for marrow with crude tools, Harmand says.

“We don’t know if Lucy was a toolmaker,” Harmand emphasizes.
“Unfortunately for her, she has a lot of competition” from other
hominins alive at the time. So far the team has reported only a
single, strange-looking molar found with the tools, although other
teeth and fossils may be published soon and could clarify the
toolmaker’s identity.

Others have suggested Lucy’s kind could have made tools. Back in
2010, Alemseged and Shannon McPherron of the Max Planck Institute for
Evolutionary Anthropology wrote in _Nature_ that a rib and a shaft
of an ungulate leg bone bear “unambiguous evidence” of stone tool
marks, made 3.4 million years ago by a member of the human family. The
butchered bones were found at Dikika, just 222 meters from the spot
where Alemseged discovered the remarkably complete Dikika child. White
and others, however, argue the cut marks could be the work of
crocodile teeth rather than stone tools. And no tools have been found
at Laetoli or Hadar, where most of the hundreds of _A.
afarensis_ fossils have been found, says paleoanthropologist Terry
Harrison of New York University.

Still, Lucy’s adaptability is clear from studies of the ancient
environments she lived in for hundreds of thousands of years. Teams of
researchers are identifying ancient animals from bones and proteins
and studying pollen, plant waxes, and isotopes to reconstruct
vegetation and rainfall. They’ve found that when the earliest _A.
afarensis_ lived at Hadar about 3.7 million years ago, the site
included woods along the shore of an ancient river, where animals
waded into floodwaters and an entire family of _A. afarensis_ died
together.

Later, after 3.2 million years ago, Hadar was much drier, and Lucy’s
species adapted to a new diet with tougher foods such as sedges,
roots, and grasses; apparently in response, male members of _A.
afarensis_ evolved bigger jaws. Farther south at Laetoli the habitat
was even drier—a “marginal environment” without a stream
when _A. afarensis_ was there, says IHO paleoanthropologist Denise
Su. “Basically, _afarensis_ was a generalist,” able to survive
in a host of environments, Reed says.

CREDITS: (GRPAHIC) D. AN-PHAM/SCIENCE; (DATA) F. SPOOR, NATURE,
10.1038/521432A (2015)

Zeresenay Alemseged cradles the skull of “Lucy’s child,” a
toddler of her species he found at Dikika in Ethiopia. PHOTO: EALISA
WESTERHOFF/AFP VIA GETTY IMAGES

Lucy’s species was the only known hominin at Hadar. Yet only 30
kilometers away at Woranso-Mille, it shared the steeper, more wooded
terrain with _A. anamensis_ and _A. deyiremeda_, as well as the
owner of the Burtele foot. Reed and Haile-Selassie aim to figure out
why one site has so many hominins and the other only one.
Haile-Selassie thinks the greater diversity of habitat at
Woranso-Mille may have allowed different hominins to coexist in
different niches. He was back in the field in February, seeking more
bones and tools.

Yet even as he searches for fossils to supplant her, he and others say
Lucy’s reign continues. “I don’t think there has been anything
that has successfully displaced Lucy,” Wood says. “That doesn’t
mean she was the ancestor of _Homo_. But she’s still the best
candidate.”

That’s good news for Johanson, now 80 and just back from Ethiopia,
where he found many young people still eager to take selfies with
Lucy’s discoverer. Wherever Lucy ultimately lands in the human
family tree, Johanson has only one regret: He didn’t get to
introduce her to the Beatles.

_ANN GIBBONS, the primary writer on human evolution
for Science magazine for more than a decade, has taught science
writing at Carnegie Mellon University. She has been a Knight Science
Journalism Fellow at Massachusetts Institute of Technology and a
Science Journalism Fellow at the Marine Biological Laboratory in Woods
Hole, Massachusetts. She lives in Pittsburgh, Pennsylvania.
www.anngibbons.com [[link removed]]_

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Known as the Great Oxygenation Event, Earth froze over as oxygen
accumulated in our atmosphere, nearly driving all life extinct.
STARTS WITH A BANG / BIG THINK
April 1, 2024

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