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Olorgesailie Prehistoric Site is located on the floor of the Great Rift Valley between two extinct volcanoes, Mt. Olorgesailie and Oldonyo Esakut to the south-west of Nairobi, Kenya. Olorgesailie area is in a lake basin that existed during the latter part of the middle Pleistocene period, probably between 200,000 and 100,000 years ago. Discovered by Louis and Mary Leakey in the 1940s, Olorgesailie was excavated by Glynn Isaac as his dissertation research during the 1960s.
Olorgesailie has important evidence that concerns the habits and activities of early prehistoric peoples of the hand axe culture. The site has the highest concentration of hand axes probably compared to any other place in the world. Olorgesailie has excellently preserved biological and cultural evidence about the evolution of man. Human tools are the most prominent of all fossils in the area and the accumulation of tool represents the actual camping places of early men. It shows the evidence of human activity consistently between 1.2 million years to 400,000 years before present. This is evidence that human species had a tropical origin and a higher primate group was confined to this part of the world thus, Olorgesailie gives evidence not only of local importance but also of international significance. Scientifically, the site also has much to do with archaeological, palaeontological and geological significance.
Several butchering localities have been discovered at Olorgesailie. They are marked by concentrations of bone fragments of extinct animals and hand axes and other stone tools deposited over about 100,000 years on the shifting shoreline of a now-extinct lake. Palaeo-anthropological and geological researches so far conducted at the site indicate Olorgesailie was located close to a large shallow lake that attracted wild animals like extinct forms of hippo, elephant, zebra, giraffe, and baboon (theropithecus). Subsequent investigations by the late Glynn Isaac resulted in the uncovering of the stone artifacts and fossils exhibited in situ at the site.
Recent investigations have recovered fossil hominid remains at the site, including a partial skull in the same stratigraphic level with two Acheulean hand axes and several flakes, and adjacent to dense deposits of hand axes. This skull represents an adult Homo erectus, although some how smaller than most others of that species.
(iii): Mt. Olorgesailie is also important to the surrounding community, the Maasai. Though no longer practiced, it was used by the Ilkeekonyokie Maasai to perform sacrifices to their God -Enkai.
(viii): Olorgesailie Prehistoric site is among the few places in the world with rich archaeological and paleontological evidence that offers opportunity for detailed scientific studies into the ecological changes during the middle Pleistocene period. It probably has the highest concentration of hand axes than any other place in the world. The artifacts further provide us with very useful clues about the economic and cultural behaviour of the ancestral hominids and Homo erectus consistently between 1.2 million years ago and 400,000 years ago.
Olorgesailie Prehistoric site is run and managed by the National Museums of Kenya. It was gazetted as a prehistoric site in 1970 and is in a good conservation state.
Olorgesailie can be compared to rich fossil World Heritage Listed sites such Peking Man Site at Zhoukoudian in China (listed in 1987), The Sangiran Early Man site in Java (listed in 1996) and Fossil hominid Sites of Sterkfontain, because of its excellent preserved biological and cultural evidence on the evolution of human kind. However, unlike the other fossil sites Olorgesailie has a massive accumulation of human tools found in situ within a locality.