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The Great Rift Valley of East Africa is famous for its sites of early human habitation. One of the most remarkable sites is located at the foot of Mount Olorgesailie in Kenya, where the Smithsonian Institution has been excavating early human remains and artifacts for 19 years under the direction of Dr. Richard Potts, Director of the Human Origins Program. In addition to the human artifacts, many fossilized animal and plant species provide a reference for accurate dating of the discoveries. The geological formations help in identifying the age of the artifacts. There have been very old early human fossils found – from 3 million to 1.5 million years – but there is a big gap between 1.5 million years and about 500,000 years in the fossil record.

greatrift_1The Olorgesailie site is very important because it is the first site where evidence of humans was found from this time gap. Homo erectus, an early human species, hunted in groups for large game; finding evidence of this is one of the earliest examples of such organized game hunting and processing. One of the projects at this excavation site was to evaluate the hunting activities of Homo erectus at the edge of the marsh.

It is widely accepted that modern humans evolved over millions of years from an ancestor we share with modern apes. Although we are clearly different from apes, it is not exactly clear when we began to separate from the ape family. One thing that does appear to separate us from apes is the use of tools. Early humans left a trail of tools; we can now trace our tool advancement, and therefore the spread of man.

The earliest, simplest human tools were found in Ethiopia. These were stone flakes and pebbles or small rocks with sharp edges used as choppers to get at meat. Larger tools known as hand axes came next; they could be used to dig, chop, or cut.

As time progressed, hand axes became much better with more detail. Eventually humans developed other tools, but hand axes dominated for more than a million years.

The Olorgesailie site is located about 1.5 hours outside of Nairobi, in a hot, dry, and dusty environment about 3,000 feet above sea level. Excavation takes place in the dry season, when there are no mosquitoes. The area around Olorgesailie was once a great lake and marsh that would draw animals and early man searching for water. Dr. Potts began leading the team for excavation of early human remains and artifacts at this site when his good friend, Dr. Richard Leakey, suggested the spot to him as one with potential.

greatrift_2Dr. Potts has a theory that humans survived despite being small and vulnerable because they could adapt more easily than other more specialized animals. If a large herbivore suddenly lost its source of plants, it would have to adapt significantly or become extinct. When temperatures changed and the environment became dryer or colder, man survived because of a varied diet that did not rely on only one type of food. In fact, these sudden climate changes happened quite often over the past few million years. The fossil record proves this, as do geological formations and molecular biological evaluations of plants and animals. This is very interesting because the global warming that is causing so much alarm today may be at least partly due to a normal pattern of climate change found throughout human history.

greatrift_3One very puzzling fact in the Rift Valley is the relative lack of actual human remains despite a great deal of tools and evidence of human presence. Dr. Potts theorized that perhaps early man lived up in the hills and only came down to the lake to hunt, returning to the safety of the hills afterward. Sure enough, early in his research, he found a skull that has since become quite famous in the transition zone between the highlands and the lake. This and other findings make Olorgesailie a very special place to study.

My son Tim and I spent five days with Dr. Potts and other noted Smithsonian scientists such as Dr. John Yellen, Archaeology Program Director for the National Science Foundation; and Dr. Alison Brooks, Professor and Chair of the Anthropology Department at The George Washington University. Also with us was Dr. Kay Behrensmeyer, a research paleobiologist and Co-Director of the Evolution of Terrestrial Ecosystems, and other accomplished anthropologists and postdoctoral students. We were able to excavate early human artifacts and animal fossils from a 990,000-year-old game trail at a site where the game was processed. We collected and labeled stone flakes and ribs, humerus bones, and vertebrae of antelopes from the marsh at the edge of a great lake that periodically appeared and disappeared. At this site was an elephant skeleton (Elephas reckii) that may have been hunted by early humans. greatrift_4We found hippopotamus tracks beneath the elephant, suggesting this was a trail.

During the course of our stay we visited the site of a den of ancient hyenas representing a new species. This den had a system of burrows with many small animal bones inside. We found hand axes on the trail – quite a thrill despite their abundance in the area – and especially intriguing was the site of the oldest known human quarry. Dating back to 990,000 years, this site had more than 10,000 stone chips and dust from the industry of making hand axes and other tools. There was a fascinating cross section of geological strata attesting to the upheaval and dramatic environmental changes over the millennia.

We are indebted to Dr. Potts for his excellent hospitality and for a truly memorable experience. We continued on to Tanzania to observe game; we were rewarded with a charging lion and a charging elephant on two separate days. The game viewing was spectacular, but by far the most interesting part of this trip was the time spent with Dr. Potts and the Smithsonian scientists.