Olduvai Gorge
Olduvai Gorge, Olduvai also spelled Olduwai, paleoanthropological site in the eastern Serengeti Plain, within the boundaries of the Ngorongoro Conservation Area in northern Tanzania. It is a steep-sided ravine consisting of two branches that have a combined length of about 30 miles (48 km) and are 295 feet (90 metres) deep. 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. Although Olduvai Gorge has often been called the “Cradle of Mankind,” a different World Heritage site called the “Cradle of Humankind” is located in South Africa. Compare Sterkfontein, Swartkrans, and Kromdraai.
The Olduvai fossil beds accumulated in a lake basin between 4 and 9 miles (7 and 15 km) in diameter. The lake is underlain by volcanic rocks of the Pliocene Epoch (5.3 million to 2.6 million years ago) and, farther below, by metamorphic deposits of Precambrian time (more than roughly 542 million years ago). Relatively continuous rift-valley fault movements and volcanic action left Olduvai deeply incised. Water flow through the gorge further eroded the rock, exposing a delineated sequence of strata from which evolutionary events could be traced. Seven major stratigraphic units, or formations, have been distinguished. From the oldest to the youngest they are: Bed I (about 1.7 million to 2.1 million years old), Bed II (1.15 million to 1.7 million years old), Bed III (800,000 to 1.15 million years old), Bed IV (600,000 to 800,000 years old), the Masek Beds (400,000 to 600,000 years old), the Ndutu Beds (32,000 to 400,000 years old), and the Naisiusiu Beds (15,000 to 22,000 years old).
Bed I is at most 197 feet (60 metres) thick. It consists largely of lava flows, volcanic ash deposits, and detrital sediments. The upper part of the bed (1.7 million to 1.85 million years old) contains a rich and varied fauna and archaeological sites of the Oldowan industry. It was there in 1959 that English-born archaeologist Mary Leakey discovered a skull fragment belonging to an early hominin that her husband, Louis Leakey, named Zinjanthropus boisei (later reclassified as Paranthropus boisei). Officially labeled OH 5 (Olduvai Hominid 5) but dubbed “Nutcracker Man” because of its huge molars (indicative of a vegetarian diet), the skull was dated to about 1.75 million years ago. The discovery indicated that hominins evolved in Africa. Specimens of Homo habilis, a more humanlike species, were also found at Olduvai. These included OH 24, a skull popularly known as “Twiggy” because it had to be reconstructed from a flattened state.
The remains of Bed I are found principally where streams from volcanic highlands brought fresh water to the southern margin of an alkaline lake that existed at Olduvai. Conditions for preservation were unusually favourable at these sites because ashfalls from nearby volcanoes and fluctuations of the lake led to rapid burial of the hominin and associated remains. Other finds include Oldowan tools and the bones and teeth of various animals, notably medium-sized antelopes. Long animal bones and others containing marrow generally have been split and broken and often display bone-tool cut marks.
Living sites in Beds II, III, and IV generally are found in former river or stream channels. Bed II is 66–98 feet (20–30 metres) thick and consists of different rock formations separated by a disconformity, or erosional break. Only the Oldowan industry occurs below the disconformity; the so-called Developed Oldowan industry and the Acheulean industry occur above. H. habilis remains were found in the lower one-third of Bed II, and a cranium of H. ergaster (also called African H. erectus) was collected near the top of Bed II. P. boisei occurs both in upper and lower parts of Bed II.
Beds III and IV were deposited on an alluvial plain. These two units are distinct only in the eastern part of the gorge and are elsewhere combined into a single unit. The two beds have a maximum aggregate thickness of about 98 feet (30 metres) and consist almost entirely of stream-laid detrital sediment. Archaeological sites in Beds III and IV represent the Developed Oldowan and Acheulean industries. Hominin remains there are assigned to H. erectus and other species of Homo.
The Masek Beds accumulated during a period of major faulting and explosive volcanism. They are some 82 feet (25 metres) thick and consist of about equal amounts of stream-laid detrital sediment and aeolian (wind-worked) tuff. Only one archaeological site, of the Acheulean industry, is known in these beds. The Ndutu Beds were deposited during intermittent faulting, erosion, and partial filling of the gorge. They consist largely of aeolian tuffs, and their maximum thickness is 79 feet (24 metres). The Naisiusiu Beds were deposited on the sides and in the bottom of the gorge after it had been eroded to very near its present level. These deposits are as much as 33 feet (10 metres) thick and consist largely of aeolian tuff. They contain one archaeological site consisting of a microlithic tool assemblage and a H. sapiens skeleton, both of which have an age of about 17,000 years.
Louis Leakey, in full Louis Seymour Bazett Leakey, also called Louis S.B. Leakey, (born August 7, 1903, Kabete, Kenya—died October 1, 1972, London, England), Kenyan archaeologist and anthropologist, a member of the distinguished Leakey family of scholars and researchers, whose fossil discoveries in East Africa proved that human beings were far older than had previously been believed and that human evolution was centred in Africa, rather than in Asia, as earlier discoveries had suggested. Leakey was also noted for his controversial interpretations of these archaeological finds.
Born of British missionary parents, Leakey spent his youth with the Kikuyu people of Kenya, about whom he later wrote. He was educated at the University of Cambridge and began his archaeological research in East Africa in 1924; he was later aided by his second wife, the archaeologist Mary Douglas Leakey (née Nicol), and their sons. He held various appointments at major British and American universities and was curator of the Coryndon Memorial Museum in Nairobi from 1945 to 1961.
In 1931 Leakey began his research at Olduvai Gorge in Tanzania, which became the site of his most famous discoveries. The first finds were animal fossils and crude stone tools, but in 1959 Mary Leakey uncovered a fossil hominin (member of the human lineage) that was given the name Zinjanthropus (now generally regarded as a form of Paranthropus, similar to Australopithecus) and was believed to be about 1.7 million years old. Leakey later theorized that Zinjanthropus was not a direct ancestor of modern man; he claimed this distinction for other hominin fossil remains that his team discovered at Olduvai Gorge in 1960–63 and that Leakey named Homo habilis. Leakey held that H. habilis lived contemporaneously with Australopithecus in East Africa and represented a more advanced hominin on the direct evolutionary line to H. sapiens. Initially many scientists disputed Leakey’s interpretations and classifications of the fossils he had found, although they accepted the significance of the finds themselves. They contended that H. habilis was not sufficiently different from Australopithecus to justify a separate classification. Subsequent finds by the Leakey family and others, however, established that H. habilis does indeed represent an evolutionary step between the australopiths (who eventually became extinct) and H. erectus, who may have been a direct ancestor of modern man.
Among the other important finds made by Leakey’s team was the discovery in 1948 at Rusinga Island in Lake Victoria, Kenya, of the remains of Proconsul africanus, a common ancestor of both humans and apes that lived about 25 million years ago. At Fort Ternan (east of Lake Victoria) in 1962, Leakey’s team discovered the remains of Kenyapithecus, another link between apes and early man that lived about 14 million years ago.
Leakey’s discoveries formed the basis for the most important subsequent research into the earliest origins of human life. He was also instrumental in persuading Jane Goodall, Dian Fossey, and Biruté M.F. Galdikas to undertake their pioneering long-term studies of chimpanzees, gorillas, and orangutans in those animals’ natural habitats. The Louis Leakey Memorial Institute for African Prehistory in Nairobi was founded by his son Richard Leakey as a fossil repository and postgraduate study centre and laboratory.
Leakey wrote Adam’s Ancestors (1934; rev. ed., 1953), Stone Age Africa (1936), White African (1937), Olduvai Gorge (1951), Mau Mau and the Kikuyu (1952), Olduvai Gorge, 1951–61 (1965), Unveiling Man’s Origins (1969; with Vanne Morris Goodall), and Animals of East Africa (1969).
