McClintock, Barbara (1902–1992)

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McClintock, Barbara (1902–1992)

Outstanding researcher in the field of genetics who discovered the way genetic material moves and alters chromosomes, and therefore heredity, winning the Nobel Prize for her pioneering work . Pronunciation: Mc-CLIN-tock. Born on June 16, 1902, in Hartford, Connecticut; died at the Huntington Hospital on Long Island, New York, on September 2, 1992; third of four children of Thomas Henry McClintock (a physician) and Sara (Handy) McClintock; graduated from Cornell University, B.S., 1923, M.A., 1925, Ph.D. in botany, 1927; never married; no children.

Awards:

honorary doctorates in science from the University of Rochester (1947), Western College (1949), Smith College (1958), University of Missouri (1968), Williams College (1972), Rockefeller University (1979), Harvard University (1979). Kimber Genetics Award, National Academy of Sciences (1967); National Medal of Science (1970); Rosenstiel Award from Brandeis University (1978); Albert Lasker Basic Medical Research Award (1981); Wolf Foundation Prize from Israel (1981); (shared with Susumu Tonegawa) Horwitz Prize, Columbia University (1982); MacArthur Laureate Award (annual lifetime award, $60,000 tax-free); Nobel Prize in Physiology or Medicine (1983).

Following the birth of her brother (1904), lived periodically with her father's aunt and uncle in Massachusetts; family moved to the Flatbush section of Brooklyn, New York (1908); graduated Erasmus Hall High School, Brooklyn (1918); worked in an employment agency; enrolled in Cornell University (1919), majoring in biology; studied graduate-level genetics while working on her bachelor's degree; began studies of plant genetics at Cornell which had an active research program in the Agriculture College; worked with maize (Indian corn); granted doctorate at age 25 (1927); began publishing research papers (1929); awarded fellowship by the National Research Council; divided time conducting research for two years at Cornell University, the University of Missouri, and the California Institute of Technology; received Guggenheim fellowship to work in Berlin at the Kaiser Wilhelm Institute (1933); returned to U.S. after witnessing rise of Nazism in Germany; worked in research at Cornell; became assistant professor at the University of Missouri (1936), teaching and conducting research; became vice-president of the Genetics Society of America (1939); began working at the Cold Spring Harbor Laboratory on Long Island, New York (1941); joined staff of the Carnegie Institution (1941–67); became president of the Genetics Society of America (1944); experimented with chromosomes in maize (1940s), making many original discoveries; presented findings (1951); trained Latin American cytologists in methods of conducting research of maize (1958–60); appointed Andrew White professor-at-large by Cornell University (1965); gained recognition for her discoveries (1970s); worked at Cold Spring Harbor Laboratory until the end of her life.

Selected writings:

The Discovery and Characterization of Transposable Elements: The Collected Papers of Barbara McClintock (NY: Garland Press, 1987); many journal articles and speeches.

Barbara McClintock, who conducted research in genetics, made immensely important discoveries about the nature of genes and chromosomes years before other researchers. She found that genes can move around chromosomes to form new heredity patterns, a discovery that did not fit the prevailing thinking which pictured genes as fixed and stable segments of chromosomes. McClintock worked independently and intensely, and for a long time her work was not understood by her peers, though she was well respected in the field. She persisted throughout her life in her goal of conducting important research in a male-dominated field that discouraged women from attaining leadership roles. Recognition that Barbara McClintock was one of the geniuses in the history of genetics finally came when her theories of genetic transposition were confirmed.

Barbara McClintock's mother Sara Handy McClintock came from a distinguished Massachusetts family that could trace its ancestry to the Mayflower. When Sara wanted to marry Thomas Henry McClintock, there was a great deal of opposition, because Thomas, whose parents had immigrated to the United States from Great Britain, was perceived as a foreigner. As well, he had run off to sea in his teens and was now a medical student, incapable of supporting a family. Sara married Thomas in 1898, against her father's wishes and aware that he would not aid them financially. Instead, she used some of her own funds from an inheritance and, over the years, gave piano lessons to earn income. The McClintocks were an attractive, intelligent, and compatible couple who supported each other during difficult times, especially when their children were young and Thomas was starting his medical practice.

On June 16, 1902, Barbara McClintock was born in Hartford, Connecticut, the third daughter, following sisters Marjorie and Mignon , and a disappointment to her parents who had wanted a son. She was originally called Eleanor, but that delicate appellation did not suit the independent child, so her name was changed to Barbara. Though she loved her family, she felt she did not quite belong. After a son, Malcolm Rider McClintock (called Tom), was born in 1904, the strain of raising four young children proved too trying for Sara McClintock, so Barbara was sent to live on-and-off with her father's aunt and uncle in a small town in Massachusetts. (Sara herself had lived with an aunt and uncle in California after her mother died when she was a year old.) Barbara enjoyed Massachusetts and would often accompany her uncle, a fish vendor, when he made his rounds with horse and wagon. She learned about the natural and mechanical worlds, particularly after a truck replaced the horse. When she was old enough to attend school, she moved home permanently.

The thrill comes from being intensely absorbed in the material.
—Barbara McClintock

In 1908, the McClintocks moved to Flatbush, in Brooklyn, New York, which—unlike Hartford, an already developing city—had some untouched areas that allowed the children to explore nature. The McClintocks would have agreed with some modern-day theories on child-raising; for example, they believed that children should have freedom to do what they wanted and not be bound by rules. Thomas McClintock cautioned the children's teachers that they were not to be assigned homework, and when the youngsters wanted a day off from school, or disliked a teacher, they were allowed to stay home. Barbara enjoyed playing street games with her brother and his friends; her parents had bloomers made for her so that she could be as active as a boy, playing football and climbing trees (later she would wear slacks for her work in the corn fields). McClintock had boxing gloves and ice skates as well, yet she also enjoyed spending time alone reading and thinking. Her outdoor activities irritated a neighbor who advised Barbara to take up more feminine pastimes. Sara McClintock informed the woman that she was never to interfere with her daughter again.

The McClintock youngsters attended Erasmus Hall High School, where they were good students and where Barbara discovered her love of science. During her adolescence, she felt different from her peers. She was uninterested in boys or clothes but had a keen intellectual curiosity and an eagerness to learn. Although the McClintock sisters were extremely intelligent, Sara discouraged them from attending college, believing that higher education was a hindrance to marriage. Although Barbara wanted to attend Cornell, she settled for working as an interviewer at an employment agency and studying at the library.

Thomas McClintock had been away, serving in the military as a surgeon during the First World War. At war's end in 1918, he returned home and convinced his wife to allow their third-born daughter to travel to Cornell and register. The fact that the College of Agriculture did not charge tuition may have helped, because one of Sara's arguments had been the family's lack of money.

Barbara enjoyed an active social life in college: she was elected president of the women's freshman class and became friends with a group of young women, most of whom were Jewish. She learned some Yiddish, and rejected a sorority bid when she realized that her friends would not be included. Friendly and attractive, Barbara McClintock dated frequently but soon realized that close personal attachments and marriage were not what she had in mind. She was the first woman on campus to have her hair cut short in a "shingle," causing a stir, because women wore their hair long at that time. But life was changing for women. In the United States, after many years of struggle, women won the right to vote after Congress passed the 19th Amendment to the Constitution in 1920. In the '20s, many young women began cutting their hair (the "bobbed" look), wearing pants, and smoking cigarettes, as did Barbara McClintock.

As a college senior, she played a banjo in a jazz band, but quit when she realized that she could not spare the time. McClintock found that she loved to immerse herself in her work, and chose to focus on biology. At the time, many young women were attending college, often women's colleges. In the U.S., women comprised between 30 and 40% of all graduate students during the decade, and accounted for approximately 12% of the science and engineering Ph.D.s awarded, a proportion not seen again until the 1970s.

During the 1920s, researchers at Cornell's College of Agriculture were investigating plant genetics, using maize (Indian corn), an ideal plant to analyze because kernels come in a variety of colors, blue, brown, and red, indicating to the naked eye that changes occur from generation to generation. McClintock, who studied genetics as an undergraduate, wanted to continue to do so in graduate school, but she had to remain in the botany department because women could not matriculate in the plant-breeding department that taught genetics. Lester Sharp, a cytology professor, taught McClintock methods of studying cells. She had already mastered some of the techniques and in fact had discovered how to identify the chromosomes in maize while working for another cytologist who had been trying to solve this problem for quite some time.

McClintock proved to be brilliant both at the meticulous care needed to prepare slides of the various stages of cell division in maize and at the interpretation of what was going on. "When I look at a cell," she said, "I get down in that cell and look around…. You're not conscious of anything else…. You are so absorbed that evensmall things get big.… Nothing else matters. You're noticing more and more things that most people couldn't see because they didn't go intently over each part, slowly but with great intensity…. It's the intensity of your absorption. I'm sure painters have the same thing happen right along."

McClintock's responsibilities included planting, growing, tending, and pollinating the maize plants in a field. The plants required full days of hard work: tagging, watering, and watching. Pollination had to be carefully done to ensure that only certain pollen would fertilize a particular ear of corn. If there was too much rain, the plants could be washed out and would have to be replanted. "No two plants are exactly alike," said McClintock. "They're all different, and as a consequence, you have to know that difference…. I start with the seedling, and Idon't want to leave it. I don't feel I really know the story if I don't watch the plant all the way along. So I know every plant in the field. I know them intimately, and I find it a great pleasure to know them."

Many brilliant young scientists were drawn to Cornell for their doctorates during that era because of the exciting work that was being done under the leadership of Rollins A. Emerson, the foremost maize geneticist of the day. In 1927, after attaining her doctorate, 25-year-old McClintock worked at Cornell as an instructor. Even before she finished her degree, she had become the leader of a group of doctoral students and graduates: Marcus Rhoades, George Beadle, Charles Burnham, Harold Perry, and H.W. Lee. They shared an enthusiasm for the subject, worked long hours at their research, and stimulated each other into advancing the boundaries of knowledge in the field. Said Rhoades, "I've known a lot of famous scientists. But the only one I thought really was a genius was McClintock."

In 1929, 20-year-old Harriet Creighton arrived at Cornell to undertake graduate studies, and McClintock became her mentor and friend. They worked together, designing experiments to prove that genetic material accompanies the exchange of chromosomal matter during cell division. When the well-known scientist Thomas Hunt Morgan asked them about their progress, he urged them to publish the information. Another scientist, working with fruit flies, was coming to the same conclusions, but the Cornell team published first, in 1931. McClintock would publish nine important journal articles about her work between 1929 and 1931, but her male colleagues were more assured of their future careers. A woman's options in science were limited: she could teach in a woman's college, accept an instructor's position in a university where she might be hired, or, if her husband were a scientist, assist him in his work. But she could not become a research scientist.

Rollins Emerson, who was the department chair, thought highly of McClintock's work, but the faculty refused to hire a woman to join them. Though McClintock was frustrated in her career, between 1931 and 1936 she had research fellowships at Cornell, the California Institute of Technology, and the University of Missouri. She criss-crossed the country in her Model-A Ford and was known as a daring driver.

Cornell had become home for McClintock, partly because of a friendship with Dr. Esther Parker , a physician who had treated McClintock when she was ill and had invited her to convalesce in her home, which was a temporary haven for many students. But McClintock realized, with regret, that she needed to move on, despite the support she had obtained for her research, because her position at Cornell was not permanent. In 1933, McClintock was awarded a Guggenheim fellowship to study in Berlin with Richard B. Goldschmidt, head of the Kaiser Wilhelm Institute. But the rise of Nazism and the persecution of Jews troubled her deeply, and she returned to the United States. "It was a very, very traumatic experience," she said. "I was just unprepared."

Lewis Stadler, at the University of Missouri, was raising maize from irradiated kernels because X-rays increased the speed of mutations (changes), and he asked McClintock to investigate the genetic changes in the mature plants. In doing so, she made some fundamental discoveries: that chromosomes are physically broken by X-rays and that they rejoin, sometimes in rings, sometimes breaking again. She called this the "breakage-fusion-bridge cycle." In 1936, when the University of Missouri offered McClintock a position as assistant professor, she accepted. Though she had excellent research privileges, she was not treated well and never felt a part of the faculty, despite the fact that her reputation as a geneticist continued to grow. Realizing that she would be fired if her mentor Stadler were no longer there, she left in 1941.

That summer, she joined her friend Marcus Rhoades at the Cold Spring Harbor Laboratory, a research facility on Long Island, New York. The Carnegie Institution of Washington at Cold Spring Harbor first hired McClintock for a year, and then permanently. She would work there for the rest of her life, living in a small apartment nearby but spending most of her time in her lab, corn field, or greenhouse. Always fond of mechanical things, McClintock took her microscopes apart, cleaned, and reassembled them. She took good care of her cars as well, changing her own tires until she was 80. While at Cold Spring Harbor, McClintock would receive some important recognition: she was listed in American Men of Science, became the first woman president of the Genetics Society of America, and was elected to the National Academy of Science. Only two other women had become members in 81 years.

During the 1940s, McClintock conducted the experiments that led to her discoveries of "jumping genes," the movement of genes from one place to another in the chromosomes, which thus change the expected patterns of heredity. These discoveries were in opposition to current theories of the time that held that genes were in fixed positions. Further, she found that chromosomes actually exchange genetic material, and that there are controlling factors signaling the genes to be active or passive. One of these factors was the Dissociation locus (Ds). Upon insertion next to the gene responsible for pigment production, the Ds caused that gene to stop functioning; that is, it acted as the equivalent of a mutation. Any subsequent movement of Ds to another location resulted in the restoration of the pigment-producing gene to its normal function. These discoveries were extremely important to the understanding of heredity in all living organisms.

McClintock presented her findings at Cold Spring Harbor in 1951, but the information was so new, dense, and contrary to the thinking at the time that her audience did not understand or accept her theories. She was vindicated, however, later in the 1950s, when molecular biologists, using powerful new tools (crystallographic techniques and X-ray diffraction patterns), found the basic double helix structure of DNA, which comprises genes. "Gene splicing" in the 1970s was possible because of scientists' further knowledge about genes and the technical tools that were developed: micromanipulators, enzymes, or other molecules, which accomplish the fine work of removing, cutting, and inserting the submicroscopic genes into cells.

One of the amazing facts about McClintock's work was that she used the techniques of "observation, documentation, and microscopic analysis" to uncover new data. Young scientists objected to such old-fashioned methods, but McClintock was a superb observer: she knew each corn plant intimately and understood more from her observations than other scientists. It was her amazing intellect and attunement to her work that facilitated her discoveries. McClintock was a voracious reader; she read everything from biology to biography to Tibetan Buddhism and felt that there were important roads to knowledge outside Western traditions.

From 1958 to 1960, McClintock trained cytologists from Latin America to collect and identify indigenous maize, because modern maize seeds were crowding out the native strains. She studied the geographical distribution of the corn and discovered that they formed a map of old patterns of human commerce and travel. Twice a year, for many years, she visited sites in South America where a great deal of research on maize was conducted. Always ready to learn, she prepared for her Latin American trips by mastering Spanish, which she augmented by watching Spanish television.

Many scientists who make landmark contributions to human knowledge are not honored for decades, often because their peers have not caught up to them. McClintock's recognition was characteristic: she received many honors and awards from science organizations in the 1970s and 1980s for work she had done in the 1940s, as well as the MacArthur "genius" award of $60,000 a year for life, and the Nobel Prize for Medicine or Physiology in 1983, which the scientific community by then expected her to receive.

The slight, 5'-tall McClintock was known to be forthright, energetic, and private. Her biographers Evelyn Fox Keller and Sharon Bertsch McGrayne present two very different views of their subject. Keller sees McClintock as a "brilliant recluse, a mystic," but McGrayne writes that McClintock's friends "stressed that McClintock was neither a recluse nor a mystic." She herself, upon receiving the Nobel Prize, simply noted, "It may seem unfair … to reward a person for having so much pleasure, over the years, asking the maize plant to solve specific problems and then watching its responses." Barbara McClintock, whose immense intelligence and curiosity about life were coupled with a wry sense of humor, lived a full life, working until the end, dying of old age in her 90th year.