Olduvai Gorge, or Oldupai Gorge, in Tanzania is one of the most important paleoanthropological sites in the world; it has proven invaluable in furthering
understanding of early human evolution.
A steep-sided ravine in the Great
Rift Valley that
stretches across East Africa, it is about 48 km (30 mi) long, and is located in
the eastern Serengeti Plains in the Arusha Region not
far, about 45 kilometres (28 miles), from Laetoli, another important archaeological site
of early human occupation. The British/Kenyan paleoanthropologist-archeologist
team Mary and Louis
Leakey established
and developed the excavation and research programs at Olduvai Gorge which achieved great advances of
human knowledge and world-renowned status.
Homo habilis, probably the first early human species, occupied Olduvai Gorge
approximately 1.9 million years ago (mya); then came a contemporary australopithecine, Paranthropus boisei, 1.8 mya, then Homo erectus, 1.2 mya. Homo sapiens is dated to have occupied the site 17,000 years ago.
The site is significant in showing the
increasing developmental and social complexities in the earliest humans,
or hominins, largely as revealed in the production and use of stone
tools. And prior to
tools, the evidence of scavenging and hunting—highlighted by the presence of gnaw
marks that predate cut marks—and of the ratio of meat versus plant material in
the early hominin diet. The collecting of tools and animal remains in a central
area is evidence of developing social interactionand
communal activity. All these factors indicate increase in cognitive capacities at the beginning of the
period of hominidstransitioning to hominin—that is, to human—form and behavior.
Research
German neurologist Wilhelm Kattwinkel traveled
to Olduvai Gorge in 1911,[1] where he observed many fossil bones of an extinct three-toed
horse. Inspired by Kattwinkel's discovery, German geologist Hans
Reck led a team to
Olduvai in 1913. There, he found hominin remains, but the start of World
War I halted his
research. In 1929, Louis
Leakey visited
Reck and viewed the Olduvai fossils; he became convinced that Olduvai Gorge
held critical information on human origins, and he proceeded to mount an
expedition there.
Louis and Mary
Leakey are
responsible for most of the excavations and discoveries of the hominin
fossils in Olduvai Gorge. Their finds and research in East
Africa and the
prior work of Raymond Dart and Robert
Broom in South
Africa eventually convinced most paleoanthropologists that humans did indeed
evolve in Africa. In 1959, at the Frida Leakey Korongo (FLK) site (named after
Louis' first wife), Mary Leakey found remains of the robust
australopithecine Zinjanthropus boisei (now known as Paranthropus boisei)—which she dubbed the "Nutcracker
Man"; its age, 1.75 million years, radically altered accepted ideas about
the time scale of human evolution.
In addition to an abundance of faunal remains the Leakeys found more than 2,000
stone tools and lithic flakes, most of which they classified as Oldowan (of Olduvai) tools. In 1960, the
Leakeys' son Jonathan found a jaw fragment that proved to be the first fossil
specimen of Homo habilis.
Researchers have dated Olduvai Gorge
layers with radiometric dating of
the embedded artifacts, using potassium-argon and argon-argonmethodology. Geologist Richard L. Hay studied the Olduvai
Gorge and surrounding region between 1961 and 2002. His findings revealed that
the site once contained a large lake, with shores covered by deposits of volcanic
ash. Around 500,000
years ago, seismic activitydiverted a nearby stream which proceeded to cut down through
the sediments, revealing seven main layers in the walls of the gorge.
The name Olduvai is a misspelling
of Oldupai
Gorge, which was adopted as
the official name in 2005. Oldupai is the Maasai word
for the wild sisal plant Sansevieria ehrenbergii, which grows in the gorge.
Occupation
Homo habilis occupied Olduvai from 1.9 mya. The
australopithecine Paranthropus
boisei was found to occupy the site
from approximately 1.8 until 1.2 mya. Remains of Homo erectus have been dated at the site from 1.2 mya until
700,000 years ago. Homo
sapiens came to occupy the gorge
some 17,000 years ago.
In the 1930s, as Mary and Louis Leakey
opted to search for stone tools in East
Africa, many, if not
most, scholars were skeptical that Africa was the place where humans evolved.
The Leakeys soon turned the evidence that confirmed their intuition. They found
stone tools in the lowest (oldest) geological beds (see below). These tools
presented both shaped edges and sharp points; and lithic
flakes—struck off the
core stone in the intentional shaping of those points and edges—were found in
copious amounts.
The Leakeys mapped locations where the
tools were found and the sites where the unprocessed materials (stone cobbles) originated. They determined that some tools were
found to have been transported up to nine miles from the place of origin, which
suggested cognitive capacities to think and plan, and to execute, with abstract
thought and purpose of mind. The Oldowan tools were found in the same stratum as the Australopithecusspecimen, but the large number of other
hominin fossils dating back to two mya complicated the discussion as to which
species was, in fact, the toolmaker.
The first species found by the
Leakeys, Zinjanthropus boisei or Australopithecus boisei(renamed and still debated as Paranthropus boisei), featured a sagittal crest and
large molars, which attributes suggested the species engaged in heavy
chewing, indicating a diet of
tough plant material, including tubers, nuts, and seeds—and possibly large quantities of grasses and sedges.
Conversely, the Leakeys' 1960s finds
presented different characteristics. The skull lacked of a sagittal crest and
the braincase was much more rounded, suggesting it was not
australopithecine. The larger braincase suggested a larger brain capacity than
that of Australopithecus boisei. These important differences indicated a different species, which
eventually was named Homo habilis. Its larger brain capacity and decreased teeth size pointed to Homo as the probable toolmaker.
The oldest tools at Olduvai, found at
the lowest layer and classified as Oldowan, consists of pebbles chipped on one
edge.[4]Above this layer, and later in time, are
the true hand-axe industries, the Chellean and the Acheulean. Higher still (and later still) are
located Levallois artifacts, and finally the Stillbay implements.[4] Oldowan tools in general are
called "pebble tools" because the blanks chosen by the stone knapper
already resembled, in pebble form, the final product.[5] Mary Leakey classified the Oldowan
tools according to usage; she developed Oldowan A,B, and C categories, linking
them to Modes 1, 2, and 3assemblages classified according to mode of manufacture. Her
work remains a foundation for assessing local, regional, and continental
changes in stone tool-making during the early Pleistocene, and aids in
assessing which hominins were responsible for the several changes in stone tool
technology over time.[6]
It is not known for sure which hominin
species was first to create Oldowan tools. The emergence of tool culture has
also been associated with the pre-Homo species Australopithecus garhi,[7] and its flourishing is associated
with the early species Homo habilis and Homo ergaster. Beginning 1.7 million years ago, early Homo erectus apparently inherited Oldowan technology and refined it into the
Acheulean industry.
Dating of beds
Oldowan tools occur in Beds I–IV at
Olduvai Gorge. Bed I, dated 1.85 to 1.7 mya, contains Oldowan tools and fossils
of Paranthropus boisei and Homo habilis, as does Bed II, 1.7 to 1.2 mya. H. habilis gave way to Homo erectus at about 1.6 mya, but P. boisei persisted. Oldowan tools continue
to Bed IV at 800,000 to 600,000 before present (BP). A
significant change took place between Beds I and II at about 1.5 mya. Flake
size increased, the length of bifacial edges (as opposed to single-face edges)
occurred more frequently and their length increased, and signs of battering on
other artifacts increased. Some likely implications of these factors, among
others, are that after this pivotal time hominins used tools more frequently,
became better at making tools, and transported tools more often.
Unprocessed materials
Lava and quartz were used to make tools in Olduvai
Gorge. Only in the period 1.65 to 1.53 ma was chert used, and it presents a
significant difference in appearance among the assemblages of Olduvai Gorge.
Hunters or scavengers?
Though substantial evidence of hunting
and scavenging has been discovered at Olduvai Gorge, it is believed by
archaeologists that hominins inhabiting the area between 1.9 and 1.7 mya
spent the majority of their time gathering wild plant foods, such as berries, tubers and roots. The earliest hominins most likely did
not rely on meat for the bulk of their nutrition. Speculation about the amount of meat
in their diets is inferred from comparative studies with a close relative of
early hominins: the modern chimpanzee. The chimpanzee's diet in the wild
consists of only about five percent as meat. And the diets of modern
hunter-gatherers do not include a large amount of meat. That is, most of
the calories in both groups' diets came from plant sources. Thus, it
can be assumed that early hominins had similar diet proportions, (see the middle-range theory or bridging arguments—bridging arguments are used by
archaeologists to explain past behaviors, and they include an underlying
assumption of uniformitarianism.)
Much of the information about early
hominins comes from tools and debris piles of lithic flakes from
such sites as FLK-Zinjanthropus in Olduvai Gorge. Early hominins selected
specific types of rocks that would break in a predictable manner when
"worked", and carried these rocks from deposits several miles away.
Archaeologists such as Fiona Marshall fitted rock fragments back together like
a puzzle. She states in her article "Life in Olduvai Gorge" that
early hominins, "knew the right angle to hit the cobble, or core, in order
to successfully produce sharp-edged flakes ...". She noted that selected
flakes then were used to cut meat from animal carcasses, and shaped cobbles
(called choppers) were used to extract marrow and to chop tough plant material.
Bone fragments of birds, fish, amphibians, and large mammals were found at the FLK-Zinj site,
many of which were scarred with marks. These likely were made by hominins
breaking open the bones for marrow, using tools to strip the meat, or by carnivores having gnawed the bones. Since
several kinds of marks are present together, some archaeologists including
Lewis Binford think that hominins scavenged the meat or marrow left over from
carnivore kills. Others like Henry Bunn believe the hominins hunted and killed
these animals, and carnivores later chewed the bones.[10] This issue is still debated today,
but archaeologist Pat Shipman provided evidence that scavenging was probably
the more common practice; she published that the majority of carnivore teeth
marks came before the cut marks. Another finding by Shipman at FLK-Zinj is that
many of the wildebeest bones found there are over-represented by adult and
male bones; and this may indicate that hominins were systematically hunting
these animals as well as scavenging them. The issue of hunting versus gathering
at Olduvai Gorge is still a controversial one.