On a promontory high above the sweeping grasslands of the
Georgian steppe, a medieval church marks the spot where humans have come
and gone along Silk Road trade routes for thousands of years. But 1.77
million years ago, this place was a crossroads for a different set of
migrants. Among them were saber-toothed cats, Etruscan wolves, hyenas
the size of lions—and early members of the human family.
Here, primitive hominins poked their tiny heads into
animal dens to scavenge abandoned kills, fileting meat from the bones of
mammoths and wolves with crude stone tools and eating it raw. They
stalked deer as the animals drank from an ancient lake and gathered
hackberries and nuts from chestnut and walnut trees lining nearby
rivers. Sometimes the hominins themselves became the prey, as gnaw marks
from big cats or hyenas on their fossilized limb bones now testify.
"Someone rang the dinner bell in gully one," says
geologist Reid Ferring of the University of North Texas in Denton, part
of an international team analyzing the site. "Humans and carnivores were
eating each other."
What was it that allowed them to move out of Africa without fire, without very large brains? How did they survive?
This is the famous site of Dmanisi, Georgia, which offers an
unparalleled glimpse into a harsh early chapter in human evolution, when
primitive members of our genus Homo struggled to survive in a
new land far north of their ancestors' African home, braving winters
without clothes or fire and competing with fierce carnivores for meat.
The 4-hectare site has yielded closely packed, beautifully preserved
fossils that are the oldest hominins known outside of Africa, including
five skulls, about 50 skeletal bones, and an as-yet-unpublished pelvis
unearthed 2 years ago. "There's no other place like it," says
archaeologist Nick Toth of Indiana University in Bloomington. "It's just
this mother lode for one moment in time."
Until the discovery of the first jawbone at Dmanisi 25 years ago,
researchers thought that the first hominins to leave Africa were
classic H. erectus (also known as H. ergaster in
Africa). These tall, relatively large-brained ancestors of modern humans
arose about 1.9 million years ago and soon afterward invented a
sophisticated new tool, the hand ax. They were thought to be the first
people to migrate out of Africa, making it all the way to Java, at the
far end of Asia, as early as 1.6 million years ago. But as the bones and
tools from Dmanisi accumulate, a different picture of the earliest
migrants is emerging.
By now, the fossils have made it clear that these pioneers were
startlingly primitive, with small bodies about 1.5 meters tall, simple
tools, and brains one-third to one-half the size of modern humans'. Some
paleontologists believe they provide a better glimpse of the early,
primitive forms of H. erectus than fragmentary African fossils.
"I think for the first time, by virtue of the Dmanisi hominins, we have
a solid hypothesis for the origin of H. erectus," says Rick
Potts, a paleoanthropologist at the Smithsonian Institution's National
Museum of Natural History in Washington, D.C.
The trail of the little people
Short and small-brained, even compared with classic Homo erectus, the Dmanisi people or their immediate ancestors emerged from Africa and migrated thousands of kilometers into Asia.
Garvin Grullón
This fall, paleontologists converged in Georgia for "Dmanisi
and beyond," a conference held in Tbilisi and at the site itself from
20–24 September. There researchers celebrated 25 years of discoveries,
inspected a half-dozen pits riddled with unexcavated fossils, and
debated a geographic puzzle: How did these primitive hominins—or their
ancestors—manage to trek at least 6000 kilometers from sub-Saharan
Africa to the Caucasus Mountains? "What was it that allowed them to move
out of Africa without fire, without very large brains? How did they
survive?" asks paleoanthropologist Donald Johanson of Arizona State
University in Tempe.
They did not have it easy. To look at the teeth and jaws of the
hominins at Dmanisi is to see a mouthful of pain, says Ann
Margvelashvili, a postdoc in the lab of paleoanthropologist Marcia Ponce
de León at the University of Zurich in Switzerland and the Georgian
National Museum in Tbilisi. Margvelashvili found that compared with
modern hunter-gatherers from Greenland and Australia, a teenager at
Dmanisi had dental problems at a much younger age—a sign of generally
poor health. The teen had cavities, dental crowding, and hypoplasia, a
line indicating that enamel growth was halted at some point in
childhood, probably because of malnutrition or disease. Another
individual suffered from a serious dental infection that damaged the
jawbone and could have been the cause of death. Chipping and wear in
several others suggested that they used their teeth as tools and to
crack bones for marrow. And all the hominins' teeth were coated with
plaque, the product of bacteria thriving in their mouths because of
inflammation of the gums or the pH of their food or water. The dental
mayhem put every one of them on "a road to toothlessness," Ponce de León
says.
To the ends of earth
By following a trail of stone tools and fossils, researchers have traced possible routes for the spread of early Homo out of Africa to the far corners of Asia, starting about 2 million years ago.
Garvin Grullón
They did, however, have tools to supplement their frail bodies.
Crude ones—but lots of them. Researchers have found more than 15,000
stone flakes and cores, as well as more than 900 artifacts, in layers of
sediments dating from 1.76 million to 1.85 million years ago. Even
though H. erectus in East Africa had invented hand axes, part
of the so-called Acheulean toolkit, by 1.76 million years ago, none have
been found here at Dmanisi. Instead, the tools belong to the "Oldowan"
or "Mode 1" toolkit—the first tools made by hominins, which include
simple flakes for scraping and cutting and spherical choppers for
pounding. The Oldowan tools at Dmanisi are crafted out of 50 different
raw materials, which suggests the toolmakers weren't particularly
selective. "They were not choosing their raw material—they were using
everything," says archaeologist David Zhvania of the Georgian National
Museum.
That simple toolkit somehow enabled them to go global. "They were
able to adjust their behavior to a wide variety of ecological
situations," Potts says. Perhaps the key was the ability to butcher meat
with these simple tools—if hominins could eat meat, they could survive
in new habitats where they didn't know which plants were toxic. "Meat
eating was a big, significant change," says paleoanthropologist Robert
Foley of the University of Cambridge in the United Kingdom.
Even with their puny stone flakes, "these guys were badass,"
competing for meat directly with large carnivores, Toth says. At the
meeting, he pointed to piles of cobblestones near the entrance of an
ancient gully, which suggest the hominins tried to fend off (or hunt)
predators by stoning them.
Simple stone flakes, like those removed from this core, enabled the Dmanisi hominins to butcher meat.
They set their own course as they left Africa. Researchers had long thought that H. erectus swept
out of their native continent in the wake of African mammals they
hunted and scavenged. But all of the roughly 17,000 animal bones
analyzed so far at Dmanisi belong to Eurasian species, not African ones,
according to biological anthropologist Martha Tappen of the University
of Minnesota in Minneapolis. The only mammals not of Eurasian origin are
the hominins—"striking" evidence the hominins were "behaving
differently from other animals," Foley says.
Perhaps venturing into new territory allowed the hominins to hunt
prey that would not have known to fear and flee humans, suggests
paleoanthropologist Robin Dennell of the University of Exeter in the
United Kingdom. Tappen calls that an "intriguing new idea" but thinks it
should be tested. Checking the types of animal bones at other early
Homo fossil sites out of Africa could show whether the mix of prey
species changed when hominins colonized a new site, supporting a "naïve
prey" effect.
Whatever impelled them, the migrants left behind a trail of tools
that have enabled researchers to trace their steps out of Africa. There,
the oldest stone tools, likely fashioned by the first members of early
Homo, such as small-brained H. habilis, date reliably to 2.6
million years ago in Ethiopia (and, possibly, 3.3 million years in
Kenya). New dates for stone tools and bones with cutmarks at Ain
Boucherit, in the high plateau of northeastern Algeria, suggest that
hominins had crossed the Sahara by 2.2 million years ago when it was
wetter and green, according to archaeologist Mohamed Sahnouni of the
National Centre for Research on Human Evolution in Burgos, Spain. His
unpublished results, presented at the Dmanisi meeting, are the earliest
evidence of a human presence in northern Africa.
The next oldest tools are those from Dmanisi, at 1.85 million years
old. The trail of stone tools then hopscotches to Asia, where Mode 1
toolkits show up by nearly 1.7 million years ago in China and 1.6
million in Java, with H. erectus fossils. "We pick up little fractions of a current" of ancient hominin movements, Foley says.
Now the site of a medieval church, the promontory at Dmanisi
has been a crossroads for humans and animals for at least 1.8 million
years.
Ken Garrett
The identity of the people who dropped these stone breadcrumbs
is a mystery that has only deepened with study of the Dmanisi fossils.
The excavation team has classified all the hominins at the Georgia site
as H. erectus, but they are so primitive and variable that researchers debate whether they belong in H. erectus, H. habilis, a separate species, H. georgicus—or a mix of all three, who may have inhabited the site at slightly different dates.
A new reanalysis of the Dmanisi skulls presented at the meeting added
fuel to this debate by underscoring just how primitive most of the
skulls were. Using a statistics-based technique to compare their shape
and size with the skulls of many other hominins, Harvard University
paleoanthropologist Philip Rightmire found that only one of the Dmanisi
skulls—at 730 cubic centimeters—fits "comfortably within the confines of
H. erectus." The others—particularly the smallest at 546 cc—cluster more closely with H. habilis in size.
Nor did the Dmanisi hominins walk just like modern humans. A new
analysis of cross sections of three toe bones found that the cortical
bone—the dense outer layer—wasn't buttressed in the same way as it is in
the toes of modern humans. When these hominins "toed off," the forces
on their toes must have been distributed differently. They may have
walked a bit more like chimps, perhaps pushing off the outside edge of
their foot more, says Tea Jashashvili of the University of Southern
California in Los Angeles and the Georgian National Museum.
"If there are so many primitive traits, why are they calling it H. erectus?"
asks Ian Tattersall, a paleoanthropologist at the American Museum of
Natural History in New York City. "People are avoiding the question of
what H. erectus is. Every time new stuff comes up, they're
enlarging the taxon to fit new stuff in." Foley ventures: "I haven't the
slightest idea of what H. erectus means."
Fossils and scientists mingle at the Georgian National Museum in Tbilisi.
Indeed, H. erectus now includes the 1-million-year-old
type specimen from Trinil on the island of Java as well as fossils from
South Africa, East Africa, Georgia, Europe, and China that span roughly
300,000 to 1.9 million years. "They're putting everything into H. erectus
over huge geographical distances, essentially spread throughout the
whole world, and over a vast number of years," Johanson says.
Yet no other species matches the Dmanisi specimens better, Rightmire
says. For example, the shapes of their dental palate and skulls match
those of H. erectus, not H. habilis. And the variation
in skull size and facial shape is no greater than in other species,
including both modern humans or chimps, says Ponce de León—especially
when the growth of the jaw and face over a lifetime are considered.
Though the fossils' small stature and brains might fit best with H. habilis, their relatively long legs and modern body proportions place them in H. erectus,
says David Lordkipanidze, general director of the Georgian National
Museum and head of the Dmanisi team. "We can't forget that these are not
just heads rolling around, dispersing around the globe," Potts adds.
Like Rightmire, he thinks the fossils represent an early, primitive form
of H. erectus, which had evolved from a H. habilis–like ancestor and still bore some primitive features shared with H. habilis.
Regardless of the Dmanisi people's precise identity, researchers
studying them agree that the wealth of fossils and artifacts coming from
the site offer rare evidence for a critical moment in the human saga.
They show that it didn't take a technological revolution or a
particularly big brain to cross continents. And they suggest an origin
story for first migrants all across Asia: Perhaps some members of the
group of primitive H. erectus that gave rise to the Dmanisi people also pushed farther east, where their offspring evolved into later, bigger-brained H. erectus on Java (at the same time as H. erectus in Africa was independently evolving bigger brains and bodies). "For me, Dmanisi could be the ancestor for H. erectus in Java," says paleoanthropologist Yousuke Kaifu of the National Museum of Nature and Science in Tokyo.
In spite of the remaining mysteries about the ancient people who died
on this windy promontory, they have already taught researchers lessons
that extend far beyond Georgia. And for that, Lordkipanidze is grateful.
At the end of a barbecue in the camp house here, he raised a glass of
wine and offered a toast: "I want to thank the people who died here," he
said.
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