The 100 Most Influential Scientists of All Time (35 page)

Working primarily with the Hungarian-born physicist Leo Szilard, Fermi constructed experimental arrangements of neutron sources and pieces of uranium. They sought to determine the necessary size of a structure, the best material to use as a moderator to slow neutrons, the necessary purity of all components (so neutrons would not be lost), and the best substance for forming control rods that could absorb neutrons to slow or stop the reaction.

When the United States entered World War II in December 1941, nuclear research was consolidated to some degree. Fermi had built a series of “piles,” as he called them, at Columbia. Now he moved to the University of
Chicago, where he continued to construct piles in a space under the stands of the football field. The final structure, a flattened sphere about 7.5 metres (25 feet) in diameter, contained 380 tons of graphite blocks as the moderator and 6 tons of uranium metal and 40 tons of uranium oxide as the fuel, distributed in a careful pattern. The pile went “critical” on Dec. 2, 1942, proving that a nuclear reaction could be initiated, controlled, and stopped. Chicago Pile-1, as it was called, was the first prototype for several large nuclear reactors constructed at Hanford, Wash., where plutonium, a man-made element heavier than uranium, was produced. Plutonium also could fission and thus was another route to the atomic bomb.

In 1944 Fermi became an American citizen and moved to Los Alamos, N.M., where physicist J. Robert Oppenheimer led the Manhattan Project's laboratory, whose mission was to fashion weapons out of the rare uranium-235 isotope and plutonium. When the first plutonium bomb was tested on July 16, 1945, near Alamogordo, N.M., Fermi ingeniously made a rough calculation of its explosive energy by noting how far slips of paper were blown from the vertical.

After the war ended, Fermi accepted a permanent position at the University of Chicago, where he subsequently redirected his sights on reactions at higher energies, a field called elementary particle physics, or high-energy physics. However, Fermi went for a time back to Los Alamos to assist in the development of fusion weapons, however with the hope that they might prove impossible to construct.

Fermi primarily investigated subatomic particles, particularly pi mesons and muons, after returning to Chicago. He was also known as a superb teacher, and many of his lectures are still in print. During his later years he raised a question now known as the Fermi paradox: “Where is
everybody?” He was asking why no extraterrestrial civilizations seemed to be around to be detected, despite the great size and age of the universe. He pessimistically thought that the answer might involve nuclear annihilation.

(b. Dec. 16, 1901, Philadelphia, Pa., U.S.—d. Nov. 15, 1978, New York, N.Y.)

A
merican anthropologist Margaret Mead was noted for the force of her personality, her outspokenness, and the quality of her scientific work. Mead entered DePauw University in 1919 and transferred to Barnard College a year later. She graduated from Barnard in 1923 and entered the graduate school of Columbia University, where she studied with and was greatly influenced by anthropologists Franz Boas and Ruth Benedict (a lifelong friend). Mead received an M.A. in 1924 and a Ph.D. in 1929.

In 1925, during the first of her many field trips to the South Seas, she gathered material for the first of her 23 books,
Coming of Age in Samoa
(1928; new ed., 1968), a perennial best-seller and a characteristic example of her reliance on observation rather than statistics for data. The book clearly indicates her belief in cultural determinism, a position that caused some later 20th-century anthropologists to question both the accuracy of her observations and the soundness of her conclusions. Her other works include
Growing Up in New Guinea
(1930; new ed., 1975),
Sex and Temperament in Three Primitive Societies
(1935; reprinted, 1968),
Balinese Character: A Photographic Analysis
(1942, with Gregory Bateson, to whom she was married in 1936–51),
Continuities in Cultural Evolution
(1964), and
A Rap on Race
(1971, with James Baldwin).

During her many years with the American Museum of Natural History in New York City, she successively served
as assistant curator (1926–42), associate curator (1942–64), curator of ethnology (1964–69), and curator emeritus (1969–78). Her contributions to science received special recognition when, at the age of 72, she was elected to the presidency of the American Association for the Advancement of Science. In 1979 she was posthumously awarded the Presidential Medal of Freedom, the United States's highest civilian honour.

As an anthropologist, Mead was best known for her studies of the nonliterate peoples of Oceania, especially with regard to various aspects of psychology and culture, the cultural conditioning of sexual behaviour, natural character, and culture change. As a celebrity, she was most notable for her forays into such far-ranging topics
as women's rights, childrearing, sexual morality, nuclear proliferation, race relations, drug abuse, population control, environmental pollution, and world hunger.

Some of her other works are
Male and Female: A Study of the Sexes in a Changing World
(1949; new ed., 1975),
Anthropology: A Human Science
(1964),
Culture and Commitment
(1970),
Ruth Benedict
(1974), a biography of that anthropologist, and an autobiography of her own early years,
Blackberry Winter
(1972).
Letters from the Field
(1977) is a selection of Mead's correspondence written during the Samoa expedition.

(b. June 16, 1902, Hartford, Conn., U.S.—d. Sept. 2, 1992, Huntington, N.Y.)

A
merican scientist Barbara McClintock discovered mobile genetic elements, or “jumping genes,” which won her the Nobel Prize for Physiology or Medicine in 1983. McClintock, whose father was a physician, took great pleasure in science as a child and evidenced early the independence of mind and action that she would exhibit throughout her life. After attending high school, she enrolled as a biology major at Cornell University in 1919. She received a B.S. in 1923, a master's degree two years later, and, having specialized in cytology, genetics, and zoology, a Ph.D. in 1927. During graduate school she began the work that would occupy her entire life: the chromosomal analysis of corn (maize). She used a microscope and a staining technique that allowed her to examine, identify, and describe individual corn chromosomes.

In 1931 she and a colleague, Harriet Creighton, published “A Correlation of Cytological and Genetical Crossing-over in
Zea mays
,” a paper that established that chromosomes formed the basis of genetics. Based on her
experiments and publications during the 1930s, McClintock was elected vice president of the Genetics Society of America in 1939 and president of the Genetics Society in 1944. She received a Guggenheim Fellowship in 1933 to study in Germany, but she left early owing to the rise of Nazism. When she returned to Cornell, her alma mater, she found that the university would not hire a female professor. The Rockefeller Foundation funded her research at Cornell (1934–36) until she was hired by the University of Missouri (1936–41).

In 1941 McClintock moved to Long Island, New York, to work at the Cold Spring Harbor Laboratory, where she spent the rest of her professional life. In the 1940s, by observing and experimenting with variations in the coloration of kernels of corn, she discovered that genetic information is not stationary. By tracing pigmentation changes in corn and using a microscope to examine that plant's large chromosomes, she isolated two genes that she called “controlling elements.” These genes controlled the genes that were actually responsible for pigmentation. McClintock found that the controlling elements could move along the chromosome to a different site, and that these changes affected the behaviour of neighbouring genes. She suggested that these transposable elements were responsible for new mutations in pigmentation or other characteristics.

McClintock's work was ahead of its time and was for many years considered too radical—or was simply ignored—by her fellow scientists. Deeply disappointed with her colleagues, she stopped publishing the results of her work and ceased giving lectures, though she continued doing research. Not until the late 1960s and '70s, after biologists had determined that the genetic material was DNA, did members of the scientific community begin to verify her early findings. When recognition finally came, McClintock
was inundated with awards and honours, most notably the 1983 Nobel Prize for Physiology or Medicine. She was the first woman to be the sole winner of this award.

(Louis Leakey, b. Aug. 7, 1903, Kabete, Kenya—d. Oct. 1, 1972, London, Eng.); (Mary Douglas Leakey, b. Feb. 6, 1913, London, Eng.—d. Dec. 9, 1996, Nairobi, Kenya); (Richard Leakey, b. Dec. 19, 1944, Nairobi, Kenya)

L
ouis S.B. Leakey, Mary Douglas Leakey, and their son, Richard Leakey, respectively, heavily influenced modern archaeology and paleoanthropology. They are known for their discoveries of hominin and other fossil remains in eastern Africa. In addition to their discoveries, the family inspired several now well-known zoologists and ethologists, who have themselves made groundbreaking discoveries concerning humans and their ancestors.

Kenyan archaeologist and anthropologist Louis Seymour Bazett Leakey was known for his fossil discoveries in East Africa, which proved that humans 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, which 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.