Feb. 8, 2018
This morning we set out early for our 3+ hour drive from the eastern edge of the Ngorongoro Crater to the eastern edge of the Serengeti, driving around the southern and western rim of the crater. I was sad to leave – the Ngorongoro Sopa Lodge was very nice and the view of the crater was so beautiful. Bird songs were plentiful and the shrieks of other creatures – monkeys, hyenas – were intriguing.
But today we were going to Olduvai Gorge, a place I’ve heard about since high school, where the oldest fossilized remains of human ancestors were found – australopithecines, homo erectus, homo habilis. I’ve always found the study of human evolution fascinating. For archaeology geeks like me, Olduvai Gorge is a place of wonder.
When we reached Olduvai Gorge, I gazed down into the canyon with awe, much as I had felt seeing Machu Picchu for the first time.
A museum curator told us a little background – the real name is Oldupai, a native word that means “sisal,” an abundant plant in the area used for many purposes by the local people. Although Oldupai is the official name, worldwide it is better known as Olduvai. The very oldest fossils of human ancestors were found here, beginning in 1911, when a German scientist studying insects was passing through the gorge and saw a set of teeth – a jawbone – sticking out of the ground! And so it began. The scientist took the fossil to archaeologists to examine, which started a quest to find evidence of human evolution here. Louis Leakey proved Darwin’s theories correct when he and his wife, Mary, began digging here.
The gorge is a geological gift to archaeologists – erosion from an ancient river after volcanic activity revealed layers in distinct colors. The oldest – black volcanic soil (layer 1) – proved to be a layer full of fossilized animal bones and a creature not known before – a rather short animal who lived in trees but seemed to be partly bipedal on the ground.
Encyclopedia Britannica says, Deposits exposed in the sides of the gorge cover a time span from about 2.1 million to 15,000 years ago. The deposits have yielded the fossil remains of more than 60 hominins (members of the human lineage), providing the most continuous known record of human evolution during the past 2 million years, as well as the longest known archaeological record of the development of stone-tool industries. Olduvai Gorge was designated part of a UNESCO World Heritage site in 1979.
Each of the five layers can be dated geologically so the presence of pre-human remains, as well as ancestors of modern animals, present in those layers indicated that these animals had lived at that time. In layer 2, more remains showing evolutionary advances were found, such as the use of primitive tools. Layer 3 dated from a dry era and hominins were not found in that layer – they migrated elsewhere – but when the climate changed and that area became more fertile again, hominids returned and their evolutionary progress as well as their way of life is present in the subsequent layers (4 & 5). By the 5th layer, early homo sapiens species had arisen.
We took a quick look at the new museum – so much to read – and some of us went through taking pictures of all the information, since we didn’t have time to read it all.
Along with the hominin bones, archaeologists found animal fossils, some with tools near or embedded in them, indicating that they were hunted by the species who made the tools (pre-humans, who began making tools almost two million years ago).
The most ancient bipedal hominins were vegetarians (archaeologists know this by examining tooth fossils), but with the change in climate and migration, they adapted to the savannah ecosystem, where fewer fruits existed. This may have encouraged them to become omnivorous.
Even before rudimentary stone tools were made, the fossil record shows that bipedalism arose around 4.2 million years ago. It was bipedalism that allowed these ancient species to make and use tools (which happened about 2.6 million years ago), having their upper limbs free. Tool making in turn appears to have contributed to the evolution of the brain. If you compare the skull of Lucy above with the homo habilis skull, you can see that the homo habilis brain cavity is much larger. Lucy was a member of one of many australopithecine species, some of which may have co-existed, showing that there was not a straight line in human evolution – it was more of a mosaic than a linear process.
The genus “homo” was designated to the bigger brained, larger bodied creatures that were humans’ direct ancestors (approx. 1.8 million years ago). Human behaviors began to develop at that time, such as meat eating, food sharing, and group cooperation. These evolutionary developments are well documented by the fossils found in “Bed I” at Olduvai.
Then we went down to the Zinj site, where Mary Leakey discovered the fossilized bones of Zinjanthropus boisei (later reclassified as Paranthropus boisei),the oldest hominin ancestor ever found, in 1959. This creature lived in a wooded area, composed of grasslands and plentiful trees, and was close to a permanent source of water.
The Leakeys, after the discovery of the ancient jawbone, and their assistants, used pick axes and other tools to go through the soil. They took it from the mound on one side, sifted through it, and piled it up on the other side. (Today’s archaeologists are more meticulous, covering much smaller areas and causing less disturbance to the land.)
Even now, the Zinj site is littered with fossils. Both Anne (pictured in the foreground of the above photo) and I wandered around and found them easily enough.
Piled on the stone marker where the plaque telling about the discovery was located were fossilized and modern animal bone pieces one can handle. The giveaway as to which are ancient and which are modern is their weight: the fossils are dense and heavy (they’ve become embedded in or imbued with rock), while the modern ones are light and more starkly white.
In 1960, while excavating at another site near Zinj, the Leakeys discovered a partial skull, mandible, foot and hand remains that belonged to a more slender and bigger brained species than Paranthropus. Similar remains were found at three other Olduvai sites, leading to the publication of a new species, homo habilis, in 1964. Because of its bigger brain, it was theorized that homo habilis and not Paranthropus was the creator of the stone tools and responsible for the animals that were consumed at these early sites.