First, to find one-million-year-old sites, you have to search one-million-year-old landforms, which are often deeply buried deposits. For example, the Great Rift Valley system of eastern Africa has proven so rich in hominid and other fossils precisely because ancient and deeply buried strata are laid bare in its eroded exposures.
Second, if the artifacts and features created by chimpanzees, bonobos, and gorillas are a guide, the sites created by hominids probably were ephemeral and incompletely preserved. It is unlikely that one-million year-old termite-hunting twigs or improvised leafy nests will ever be discovered by archaeologists.
Finally, even if durable artifacts are found on ancient land surfaces, there is a good chance that such materials will have been moved about by erosion or other natural processes and the archaeological materials are no longer in their original in situ associations.
These challenges only made the sites excavated by Mary Leakey all the more exciting. In meticulous excavations conducted throughout the 1960s, Mary Leakey and her colleagues focused on a number of sites located in the oldest sediments in the main gorge at Olduvai, sediments deposited by a now-dry lake between 1.87 and 1.71 million years old. Leakey excavated in two main areas exposed by streams that cut down through Olduvai’s strata over the last 200,000 years, the DK Locality and the FLK Complex.24
The sites contained a variety of animal bones and stone artifacts: crude choppers, hammer stones, and stone flakes with utilized edges. The faunal remains were surprisingly diverse, including big game (such as ancient relatives of giraffes, elephants, rhinos, zebras, and wildebeests) as well as two species of turtles and one species of tortoise. Twenty-three different taxa of mammals were found, including a large number of crocodile teeth.
In one portion of the DK Locality, Leakey’s team discovered an amazing feature: a circular array of stones. Leakey wrote, “At DK there is a stone circle which is the earliest man-made structure known. It is built of loosely pile blocks of lava and measures three and a half to four metres in diameter. It bears a striking similarity to crude stone circles constructed for temporary shelter by present-day nomadic peoples such as the Turkana in Kenya.”25
Confessing to her own suspicions, Leaky admitted, “The Olduvai structure was a most surprising discovery in view of its age and for a while I was reluctant to believe that the blocks of lava had been artificially arranged into a circle. However, the geologists and prehistorians who have since seen the circle are almost unanimous in considering that it is likely to be the work of the early hominids and not a natural feature.”
Mary Leakey had found the oldest known house on earth.
Other archaeological projects expanded on the Olduvai discoveries, particularly at the FXJj 50 site in northern Kenya, where excavations in the 1970s and early 1980s were directed by Richard Leakey and Glynn Isaac.26 At FXJj 50 a litter of chipped stone tools and animal bones (representing mammals, birds, and fish) suggested the existence of a home base about 1.6–1.5 million years ago. Further, it was possible to fit together the chipped stone flakes and cores at the site—like pieces of a lithic jigsaw puzzle—indicating that the artifacts at FXJj 50 were largely in their original places, undisturbed by time.
Thus, the archaeological evidence indicated that by 1.5 million years ago our very ancient ancestors had developed home bases where they made tools, butchered game, shared food, and even (possibly) built simple shelters.
Or did they?
Various scholars pointed out flaws in the data from the DK Locality.27 For example, nearly half the identifiable animal bones came from crocodiles—an unlikely game animal for a small hominid armed with crude stone tools. Eighty-six percent of the crocodile bones were teeth, which crocodiles lose naturally. Other animal bones incised with cut marks from stone tools also showed evidence of being gnawed by hyenas or other carnivores. While stone flake tools and choppers showed evidence of hominid intent, it was far from certain that hominids had actually hunted game: they could have used stone tools to scavenge and scrape meat from dead game killed by other, more effective, nonhuman predators.
FIGURE 2. Site DK I, Olduvai Gorge. Redrawn from Leakey 1979.
And finally, the circular stone feature that Mary Leakey reluctantly concluded was an ancient shelter in fact consisted of chunks of the underlying bedrock jutting into the layers containing bone and stone tools. The circular pattern of bedrock blocks probably resulted from a combination of weathering and stones moved by tree roots. These were not shelter walls built by the ancient occupants of Olduvai Gorge. Mary Leakey had not found the oldest house on earth.
The archaeology of African sites dating between 2.6 and 1.6 million years ago provides a fragmentary and partial vista into the behavior of early hominids.28 While these ancestors made simple stone tools, ate meat, and carried raw materials and some food to sites, other behaviors remain unclear or in dispute. Some studies suggest that while certain Lower Stone Age sites in Africa might contain evidence for tool use and food preparation, the sites are not significantly different from the archaeological patterns potentially left by chimpanzees. Other paleoanthropologists see the same sites as evidence for hominid activity. There are relatively few of these older sites, and the archaeological evidence is frustratingly ambiguous.
It is like trying to see complex constellations on a cloudy night from the flickering light of a handful of stars. Based on such uncertain illuminations, it seems that these ancient sites were not yet homes.
. . .
The basic problem is this: there are no Paleolithic Pompeiis.29 A fundamental question that archaeologists always ask is “Are the constituents of a site really associated? Are the objects in situ and located in their original positions or rather are they out of context?” Ideally, every site would be like the ash-covered remains of ancient Pompeii: a moment frozen in time in the autumn of A.D. 79. In fact, only rarely are archaeological sites sealed deposits, intact and stilled.
A wide array of natural processes can modify or disturb an archaeological site. Bacteria and scavenging animals consume organic materials, leaving behind only indigestible stone, pottery, and bone. Flowing water—varying in volume from raindrops to flash floods—can move artifacts, cut through strata, or erode objects. Badgers, gophers, lizards, worms, and other burrowing animals change the soil matrix and move archaeological materials. As clay soils expand when wet and shrink when dry, archaeological objects are moved through the profile along with rocks and gravels.
While all archaeological sites are affected by these vagaries of preservation, the problem is most pronounced for sites from the dawn of humanity. Obviously, the oldest sites have the greatest opportunities for disturbance and decay. Further, such early sites usually have a relatively light material footprint. The sites are rarely the result of a permanent occupation because humans were highly mobile and nomadic; the archaeological record is correspondingly slight. And it may be ambiguous whether the objects and features in these early sites are the result of human actions. For example, charred wood may be from an ancient campfire or a lighting-struck tree. Cut marks on apparently butchered bones may prove to be tooth marks from nonhuman predators.
Consider the controversial site of Terra Amata, located in Nice on the French Riviera. The site was excavated over six months in 1966 after construction crews trenched into the archaeological deposit. Construction was suspended and a salvage excavation was begun, directed by Henry de Lumley.30
Terra Amata may have evidence of one of the earliest human dwellings, 350,000–450,000 years old. De Lumley and his team uncovered thousands of stone tools and flakes, an array of bones from fauna large and small, levels that contained a few postholes, small hearths, and blocks of stone and oval clusters of archaeological materials that de Lumley interpreted as the remains of ancient huts 7–15 × 4–6 meters in size. Further, de Lumley interpreted the archaeological strata as forming thin, discrete layers that represented annual reoccupations of Terra Amata by mobile hunters and gatherers camped during successive springtimes on the shore of the Mediterranean Sea. De Lumley identified eleven