Leakeys Find a 1.75-Million-Year-Old Fossil Hominid

Date July 17, 1959

L. S. B. and Mary Leakey discovered the first fossil hominid, which had lived 1.7 million years ago at Olduvai Gorge in East Africa.

Also known asZinjanthropus boisei; Paranthropus boisei; Australopithecus boisei; Nutcracker man

Locale Olduvai Gorge, northern Tanganyika (now in Tanzania)

Key Figures

• L. S. B. Leakey (1903-1972), Kenyan-born British archaeologist and paleontologist
• Mary Leakey (Mary Douglas Nicol; 1913-1996), British archaeologist

Summary of Event

Olduvai Gorge, in northern Tanzania, was discovered in 1911, when a German butterfly collector happened upon it. Within two years of its discovery, a German expedition recognized the gorge as a fossil hunter’s paradise. The gorge owes its origins to massive geological faulting approximately 100,000 years ago. As a result of the changing geology, the Great Rift Valley was formed, which stretches over sixty-four hundred kilometers in East Africa and the Middle East, from Jordan in the north through Kenya and Tanzania to Mozambique in the south. A newly formed river resulted from the rains and rapidly cut through the previously laid down strata. The strata were formed from a series of Ngorongoro and Lemagrut volcanic eruptions, combined with lake and river deposits laid down millions of years ago.

The gorge has four distinct layers, or beds, labeled Bed I (at the bottom of the gorge) through Bed IV (nearest the top). Bed I is the oldest and has been dated to be more than 2 million years old. While Olduvai is more than 40 kilometers in length and grows to a depth of approximately 92 meters, it is a small portion of the Great Rift system. The gorge passes through the surrounding Serengeti Plain, a semiarid grassland plateau, which possesses an environment similar to that of the past few million years, as documented by information within Olduvai’s strata.

L. S. B. Leakey, born to English missionary parents in Kenya and initiated into the Kikuyu tribe as a young boy, had varied interests but was ultimately trained as an anthropologist at the University of Cambridge. In 1931, he was accompanied on his first paleontological expedition to Olduvai by Hans Reck, a German geologist. Reck, who had worked at Olduvai prior to 1914, discouraged Leakey from his hope to find evidence of prehistoric human activity at the gorge; however, within the first day of their arrival, a hand ax was discovered. Leakey recorded the site of this discovery as FLK, an acronym for “Frida” Leakey, his first wife, and korongo, a Swahili word for “gully.” Leakey recognized this site as an important one, although it was to become famous twenty-eight years later with the discovery by Mary Leakey, his second wife, of their first hominid fossil, Zinjanthropus boisei.

Mary Douglas Nicol was born in England in 1913. She was a sixth-generation descendant of John Frere, a late eighteenth century antiquarian who discovered stone tools in association with the remains of extinct animals. Mary Leakey was also educated in England as an archaeologist. When she met Leakey in 1933, she was becoming well known for her illustrations of lithic tools. Indeed, it was soon after they met that Leakey asked her to undertake the drawings for the first edition of his book, Adam’s Ancestors (1934). They were married on Christmas Eve, 1936, in England, only days before their departure for Kenya.

From the late 1930’s until the discovery of their first fossil hominid in 1959, the Leakeys focused worldwide attention on prehistorians and paleontologists in East Africa with their introduction of a stone-tool technology encountered at Olduvai and with the discovery of several extinct vertebrates, including a 25-million-year-old primate, a member of the genus Proconsul. The “Oldowan” tool tradition, named for Olduvai, was introduced by the Leakeys and was dated to the Lower Pleistocene epoch, which, at the time, was believed to have begun about a million years ago. In the early 1960’s, the date for this tool tradition was revised based upon the potassium-argon radiometric-dating technique. Specifically, the technique was applied to the volcanic rocks recovered from Olduvai and prompted the age to be extended by approximately another million years. This new date was confirmed by dating methods developed later, including fission track and paleomagnetism.

On the morning of July 17, 1959, L. S. B. Leakey awoke with a headache and fever. He later wrote in National Geographic Magazine that “Mary was adamant” and said, “’I am sorry, . . . but you just cannot go out this morning, even though you want to. You’re not fit for it, and you’d only get worse. We cannot risk having to go back. . . .’” Little could anyone know that during that morning’s search of Olduvai, Mary Leakey would discover the remains for which she and her husband had long been searching: the animal believed to have made the previously discovered Oldowan tools. She had happened upon the upper dentition and a few fragments of a never-before-documented fossil hominid. The fossil was found very near the bottom of the gorge eroding out of an embankment representing Bed I.

During the next nineteen days, the Leakeys recovered more than four hundred pieces from an almost complete skull. Similar fossil hominids, presently classified as members of the genus Australopithecus, had been found previously in South Africa by Raymond Arthur Dart in 1924 and Robert Broom in 1936. Yet, firm dates could not be established for the South African finds; evidence of associated tool use was not as accurately documented as that encountered at Olduvai.

The hominid discovered by the Leakeys is suggested to have lived approximately 1.75 million years ago. The archaeologists recognized the remains as those of a young adult male based upon the degree of dental eruption and development and evidence of extreme robustness. Furthermore, the dental, facial, and cranial morphology of the Leakey discovery was distinct from the hominids previously known from South Africa. As a result, the Leakeys placed their hominid into a new taxon. Specifically, the Leakeys classified their discovery into a new genus Zinjanthropus, and species, boisei. Zinj is Arabic for East Africa, anthropus is Greek for humankind, and boisei is a latinization of Boise, the family name of Leakey’s benefactor, Charles Boise. Because of the specimen’s cranial robustness, massive molars, and “molarized” premolars, the fossil’s popular name became “Nutcracker man.”

Significance

The discovery of Zinjanthropus affected human paleontology in many ways. The age of the first hominids was pushed back dramatically. Although Dart, Broom, and others had previously given the world cause to accept the notion proposed by Charles Darwin in The Descent of Man and Selection in Relation to Sex (1871) that Africa would prove to be the cradle of humankind, the various hominid fossils recovered from South Africa (for example, Australopithecus africanus, Paranthropus robustus, and others) did not lend themselves to accurate dating. The discovery of Zinjanthropus boisei and the Oldowan tools from the volcanic contexts of Olduvai Gorge, however, allowed accurate radiometric dates to be applied. Thus, the age of this early hominid found by the Leakeys pushed the age of the earliest hominids well beyond that which previously had been suggested.

Additionally, the discovery of Zinjanthropus created controversy among paleontologists because Leakey introduced a new genus. Simply, some believed another taxonomic name was not warranted. While controversy exists among paleontologists over the interpretation of the hominid fossil record, Zinjanthropus, Australopithecus, Paranthropus, and other generic names previously introduced have been placed into the single genus Australopithecus. Furthermore, many specimens previously seen as members of distinct genera are now interpreted to be members of different species within the same genus. The issue remains in dispute, however, and some scientists refer to the species discovered by the Leakeys as “Paranthropus boisei,” while others retain the appellation “Australopithecus boisei.” “Zinjanthropus boisei,” however, is universally regarded as an outdated term.

This particular species is viewed as having been much more robust than its nearest taxonomic relatives, Australopithecus robustus and Australopithecus africanus. The latter species is the least robust of the three. Furthermore, since paleontologists define hominids as habitually bipedal higher primates that use tools (as evidenced by the location of the foramen magnum beneath the skull), with the discovery of tools in association with “Zinj,” one could no longer doubt that members of the subfamily Australopithecinae deserved to be classified as hominids.

Perhaps the most important impact of the Leakey discovery was that of public support. While the Leakeys had become well known among their scientific peers in archaeology, prehistory, and paleontology, the public became familiar with their work because of their discovery of Zinjanthropus. Most notably, the discussion of this discovery, complete with color photographs and L. S. B. Leakey’s personal account in the September, 1960, issue of National Geographic magazine, played an important role in obtaining public support in the quest to document the human paleontological record. The support offered by the National Geographic Society of Washington led to more than double the amount of earth excavated the following season. The increase in the recognition and support of paleontology has had a dramatic impact on the scientific search for human fossil ancestors.

Bibliography

Bowman-Kruhm, Mary. The Leakeys: A Biography. Westport, Conn.: Greenwood Press, 2005. Brief biographical study of Mary and L. S. B. Leakey and their contributions to paleanthropology. Bibliographic references and index.

Johanson, Donald C., and Maitland A. Edey. Lucy: The Beginnings of Humankind. New York: Simon & Schuster, 1981. A book coauthored by another prominent figure in the field of paleoanthropology. This volume offers a popular account of other hominid discoveries from the Pleistocene of East Africa. It addresses the financial problems encountered in such research as well as various strong personalities and controversies that have influenced attempts to document the human fossil record.

Leakey, Louis S. B. By the Evidence: Memoirs, 1932-1951. New York: Harcourt Brace Jovanovich, 1974. This volume addresses the period following Leakey’s research post at the University of Cambridge until 1952. His divorce from Frida, his first wife, his marriage to Mary in 1936, his work with the Kenyan Criminal Investigation Department during World War II, his and Mary’s return to paleontology following the war, and Mary’s discovery of Proconsul in 1948 are all discussed.

‗‗‗‗‗‗‗. “Finding the World’s Earliest Man.” National Geographic 118 (September, 1960): 420-435. A popular version of the original Nature article describing the site at Olduvai Gorge (FLK) and Zinjanthropus boisei. It was written for what became one of the Leakeys’ strongest supporters, the National Geographic Society, and further enhanced public support of the Leakeys’ search.

‗‗‗‗‗‗‗. “A New Fossil Skull from Olduvia.” Nature 84 (August, 1959): 491-493. This is the publication that announced the discovery of the first hominid remains recovered by the Leakeys at Olduvai Gorge. The site, the circumstances, and the fossil are described. The remains are described as being those of a young male and placed into a new genus and species, Zinjanthropus boisei.

Leakey, Richard E., and Roger Lewin. Origins. New York: E. P. Dutton, 1977. Drawing in part upon the work of his parents, Richard Leakey also discusses his paleontological discoveries at Lake Turkana in northern Kenya. This popular volume suggests that there may have been three or more species of hominids existing as contemporaries in East Africa approximately 2 million years ago. Central to the text’s theme is the question of why the lineage of Homo survived and the others did not.

Morell, Virginia. Ancestral Passions: The Leakey Family and the Quest for Humankind’s Beginnings. New York: Simon & Schuster, 1995. Exhaustive study of L. S. B., Mary, and Richard Leakey and their work in Tanzania over two generations. Bibliographic references and index.

Pfeiffer, John E. The Emergence of Humankind. 4th ed. New York: Harper & Row, 1985. Although not written in the style of most textbooks, this volume is used frequently as a textbook in introductory physical anthropology courses. It addresses the various lines of research often employed by paleoanthropologists in their attempt to learn about the hominid fossil record.