The 100 Most Influential Scientists of All Time (36 page)

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).

English-born archaeologist and paleoanthropologist Mary Douglas Leakey (née Mary Douglas Nicol) made several fossil finds of great importance in the understanding of human evolution. Her early finds were interpreted and publicized by her husband, the noted anthropologist Louis S.B. Leakey.

As a girl, Mary exhibited a natural talent for drawing and was interested in archaeology. After undergoing sporadic schooling, she participated in excavations of a Neolithic Period site at Hembury, Devon, England, by which time she had become skilled at making reproduction-quality drawings of stone tools. She met Louis Leakey in 1933, and they were married in 1936. Shortly thereafter they left for an expedition to East Africa, an area that became the central location of their work.

Working alongside Louis Leakey for the next 30 years, Mary Leakey oversaw the excavation of various prehistoric
sites in Kenya. Her skill at the painstaking work of excavation surpassed her husband's, whose brilliance lay in interpreting and publicizing the fossils that they uncovered. In 1948, on Rusinga Island in Lake Victoria, she discovered the skull of
Proconsul africanus
, an ancestor of both apes and early humans that lived about 25 million years ago. In 1959 at Olduvai Gorge, Tanzania, she discovered the skull of an early hominin (member of the human lineage) that her husband named
Zinjanthropus
, or “eastern man,” though it is now regarded as
Paranthropus
, a type of australopith, or “southern ape.”

After her husband's death in 1972, Leakey continued her work in Africa. In 1978 she discovered at Laetoli, a site south of Olduvai Gorge, several sets of footprints made in volcanic ash by early hominins that lived about 3.5 million years ago. The footprints indicated that their makers walked upright; this discovery pushed back the advent of human bipedalism to a date earlier than the scientific community had previously suspected. Among Mary Leakey's books were
Olduvai Gorge: My Search for Early Man
(1979) and the autobiographical
Disclosing the Past
(1984).

Kenyan anthropologist, conservationist, and political figure Richard Leakey was responsible for extensive fossil finds related to human evolution and campaigned publicly for responsible management of the environment in East Africa. The son of noted anthropologists Louis S.B. Leakey and Mary Leakey, Richard was originally reluctant to follow his parents' career and instead became a safari guide. In 1967 he joined an expedition to the Omo River valley in Ethiopia. It was during this trip that he first noticed the site of Koobi Fora, along the shores of Lake Turkana (Lake Rudolf) in Kenya, where he led a preliminary search that
uncovered several stone tools. From this site alone in the subsequent decade, Leakey and his fellow workers uncovered some 400 hominin fossils representing perhaps 230 individuals, making Koobi Fora the site of the richest and most varied assemblage of early human remains found to date anywhere in the world.

Leakey proposed controversial interpretations of his fossil finds. In two books written with science writer Roger Lewin,
Origins
(1977) and
People of the Lake
(1978), Leakey presented his view that, some 3 million years ago, three hominin forms coexisted:
Homo habilis, Australopithecus africanus
, and
Australopithecus boisei
. He argued that the two australopith forms eventually died out and that
H. habilis
evolved into
Homo erectus
, the direct ancestor of
Homo sapiens
, or modern human beings. He claimed to have found evidence at Koobi Fora to support this theory. Of particular importance is an almost completely reconstructed fossil skull found in more than 300 fragments in 1972 (coded as KNM-ER 1470). Leakey believed that the skull represented
H. habilis
and that this relatively large-brained, upright, bipedal form of
Homo
lived in eastern Africa as early as 2.5 million or even 3.5 million years ago. Further elaboration of Leakey's views was given in his work
The Making of Mankind
(1981).

From 1968 to 1989 Leakey was director of the National Museums of Kenya. In 1989 he was made director of the Wildlife Conservation and Management Department (the precursor to the Kenya Wildlife Service [KWS]). Devoted to the preservation of Kenya's wildlife and sanctuaries, he embarked on a campaign to reduce corruption within the KWS, crack down (often using force) on ivory poachers, and restore the security of Kenya's national parks. In doing so he made numerous enemies. In 1993 he survived a plane crash in which he lost both his legs below the knee. The following year he resigned his post at the KWS, citing interference by
Kenyan President Daniel arap Moi's government, and became a founding member of the opposition political party Safina (Swahili for “Noah's ark”). Pressure by foreign donors led to Leakey's brief return to the KWS (1998–99) and to a short stint as secretary to the cabinet (1999–2001). Thereafter he dedicated himself to lecturing and writing on the conservation of wildlife and the environment.

Another book with Roger Lewin was
The Sixth Extinction: Patterns of Life and the Future of Humankind
(1995), in which he argued that human beings have been responsible for a catastrophic reduction in the number of plant and animal species living on the Earth. Leakey later collaborated with Virginia Morell to write his second memoir,
Wildlife Wars: My Fight to Save Africa's Natural Treasures
(2001; his first memoir,
One Life
, was written in 1983). In 2004 Leakey founded WildlifeDirect, an Internet-based nonprofit conservation organization designed to disseminate information about endangered species and to connect donors to conservation efforts. He also served in 2007 as interim chair of the Kenya branch of Transparency International, a global coalition against corruption.

(b. March 4, 1904, Odessa, Russian Empire [now in Ukraine]—d. Aug. 19, 1968, Boulder, Colo., U.S.)

R
ussian-born American nuclear physicist and cosmologist George Gamow was one of the foremost advocates of the big-bang theory, according to which the universe was formed in a colossal explosion that took place billions of years ago. In addition, his work on deoxyribonucleic acid (DNA) made a basic contribution to modern genetic theory.

Gamow attended Leningrad (now St. Petersburg) University, where he studied briefly with A.A. Friedmann, a
mathematician and cosmologist who suggested that the universe should be expanding. At that time Gamow did not pursue Friedmann's suggestion, preferring instead to delve into quantum theory. After graduating in 1928, he traveled to Göttingen, where he developed his quantum theory of radioactivity, the first successful explanation of the behaviour of radioactive elements, some of which decay in seconds while others decay over thousands of years.

His achievement earned him a fellowship at the Copenhagen Institute of Theoretical Physics (1928–29), where he continued his investigations in theoretical nuclear physics. There he proposed his “liquid drop” model of atomic nuclei, which served as the basis for the modern theories of nuclear fission and fusion. He also collaborated with F. Houtermans and R. Atkinson in developing a theory of the rates of thermonuclear reactions inside stars.

In 1934, after emigrating from the Soviet Union, Gamow was appointed professor of physics at George Washington University in Washington, D.C. There he collaborated with Edward Teller in developing a theory of beta decay (1936), a nuclear decay process in which an electron is emitted. Soon after, Gamow resumed his study of the relations between small-scale nuclear processes and cosmology. He used his knowledge of nuclear reactions to interpret stellar evolution, collaborating with Teller on a theory of the internal structures of red giant stars (1942). From his work on stellar evolution, Gamow postulated that the Sun's energy results from thermonuclear processes.

Gamow and Teller were both proponents of the expanding-universe theory that had been advanced by Friedmann, Edwin Hubble, and Georges LeMaître. Gamow, however, modified the theory, and he, Ralph Alpher, and Hans Bethe published this theory in a paper
called “The Origin of Chemical Elements” (1948). This paper, attempting to explain the distribution of chemical elements throughout the universe, posits a primeval thermonuclear explosion, the big bang that began the universe. According to the theory, after the big bang, atomic nuclei were built up by the successive capture of neutrons by the initially formed pairs and triplets.

In 1954 Gamow's scientific interests grew to encompass biochemistry. He proposed the concept of a genetic code and maintained that the code was determined by the order of recurring triplets of nucleotides, the basic components of DNA. His proposal was vindicated during the rapid development of genetic theory that followed.

Gamow held the position of professor of physics at the University of Colorado, Boulder, from 1956 until his death. He is perhaps best known for his popular writings, designed to introduce to the nonspecialist such difficult subjects as relativity and cosmology. His first such work,
Mr. Tomkins in Wonderland
(1936), gave rise to the multivolume “Mr. Tomkins” series (1939–67). Among his other writings are
One, Two, Three… Infinity
(1947),
The Creation of the Universe
(1952; rev. ed., 1961),
A Planet Called Earth
(1963), and
A Star Called the Sun
(1964).

(b. April 22, 1904, New York, N.Y., U.S.—d. Feb. 18, 1967, Princeton, N.J.)

A
merican theoretical physicist and science administrator Julius Robert Oppenheimer was director of the Los Alamos laboratory during development of the atomic bomb (1943–45) and director of the Institute for Advanced Study, Princeton (1947–66). Accusations of disloyalty led to a government hearing that resulted in the
loss of his security clearance and of his position as adviser to the highest echelons of the U.S. government. The case became a cause célèbre in the world of science because of its implications concerning political and moral issues relating to the role of scientists in government.

Oppenheimer was the son of a German immigrant who had made his fortune by importing textiles in New York City. During his undergraduate studies at Harvard University, Oppenheimer excelled in Latin, Greek, physics, and chemistry, published poetry, and studied Oriental philosophy. After graduating in 1925, he sailed for England to do research at the Cavendish Laboratory at the University of Cambridge, which, under the leadership of Lord Ernest Rutherford, had an international reputation for its pioneering studies on atomic structure. At the Cavendish, Oppenheimer had the opportunity to collaborate with the British scientific community in its efforts to advance the cause of atomic research.

Max Born invited Oppenheimer to Göttingen University, where he met other prominent physicists, such as Niels Bohr and P.A.M. Dirac, and where, in 1927, he received his doctorate. After short visits at science centres in Leiden and Zürich, he returned to the United States to teach physics at the University of California at Berkeley and the California Institute of Technology.

In the 1920s the new quantum and relativity theories were engaging the attention of science. That mass was equivalent to energy and that matter could be both wavelike and corpuscular carried implications seen only dimly at that time. Oppenheimer's early research was devoted in particular to energy processes of subatomic particles, including electrons, positrons, and cosmic rays. Since quantum theory had been proposed only a few years before, the university post provided him an excellent
opportunity to devote his entire career to the exploration and development of its full significance. In addition, he trained a whole generation of U.S. physicists, who were greatly affected by his qualities of leadership and intellectual independence.

The rise of Adolf Hitler in Germany stirred his first interest in politics. In 1936 he sided with the republic during the Civil War in Spain, where he became acquainted with Communist students. Although his father's death in 1937 left Oppenheimer a fortune that allowed him to subsidize anti-Fascist organizations, the tragic suffering inflicted by Joseph Stalin on Russian scientists led him to withdraw his associations with the Communist Party—in fact, he never joined the party—and at the same time reinforced in him a liberal democratic philosophy.

After the invasion of Poland by Nazi Germany in 1939, the physicists Albert Einstein and Leo Szilard warned the U.S. government of the danger threatening all of humanity if the Nazis should be the first to make a nuclear bomb. Oppenheimer then began to seek a process for the separation of uranium-235 from natural uranium and to determine the critical mass of uranium required to make such a bomb. In August 1942 the U.S. Army was given the responsibility of organizing the efforts of British and U.S. physicists to seek a way to harness nuclear energy for military purposes, an effort that became known as the Manhattan Project. Oppenheimer was instructed to establish and administer a laboratory to carry out this assignment. In 1943 he chose the plateau of Los Alamos, near Santa Fe, New Mexico, where he had spent part of his childhood in a boarding school.

For reasons that have not been made clear, Oppenheimer in 1942 initiated discussions with military security agents that culminated with the implication that
some of his friends and acquaintances were agents of the Soviet government. This led to the dismissal of a personal friend on the faculty at the University of California. In a 1954 security hearing he described his contribution to those discussions as “a tissue of lies.”