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Demythologizing McClintock

Carla Keirns

The Tangled Field: Barbara McClintock's Search for the Patterns of Genetic Control. Nathaniel C. Comfort. xii + 337 pp. Harvard University Press, 2001. $37.50

In this ambitious biographical study of Barbara McClintock (1902–1992), historian of science Nathan C. Comfort challenges the standard interpretation of her science and her life. He seeks to dismantle what he refers to as "the McClintock myth" and reveal the active role McClintock herself played in creating it; to show that the mechanism of transposition for which she became famous was never central to her own research agenda; and to establish a new view of her place in the history of 20th-century biology.

Barbara McClintock . . .Click to Enlarge Image

Comfort has reconstructed in great detail, experiment by experiment, McClintock's work on transposons (segments of chromosomes that move from one site in the genome to another), for which she much later won the Nobel Prize in Physiology or Medicine. He spent years deciphering her cramped and faded handwriting in lab notebooks, on seed packets and in letters to her closest friends. In addition, he made extensive use of a set of 10 interviews that McClintock gave to various people, and he interviewed many of her friends and colleagues at length. Comfort suggests that his account differs substantially from earlier ones in large part because of new sources that have only recently become available, including the papers of her colleagues George Beadle, Hermann J. Muller and Marcus Rhoades, as well as McClintock's correspondence and laboratory notes, which were donated to the American Philosophical Society after her death.

According to McClintock, when she presented her discovery of transposons—which she called "controlling elements"—to an audience at the Cold Spring Harbor Laboratory's summer meeting of geneticists and molecular biologists in 1951, the response was "puzzlement, even hostility." She attributed this rejection by her colleagues, an important element of what Comfort calls her "private myth," to their close-minded attachment to old ideas. Evelyn Fox Keller, in her brief 1983 biography, A Feeling for the Organism: The Life and Work of Barbara McClintock, accepted McClintock's account of the rejection but associated it with sexism. Comfort instead challenges the whole notion that McClintock's work was rejected by her audience. He notes that she had already established herself as an outstanding researcher in maize genetics by 1927. In 1944, she was elected to the National Academy of Sciences as its third female member, and the following year she became president of the Genetics Society of America. Other scientists did take her seriously, and Comfort demonstrates that her 1951 presentation did arouse interest.

The second chapter of The Tangled Field, which describes the early details of McClintock's life, is the least satisfying of the book. Here Comfort traces the theme of a desire for freedom in her work and life, concluding that this emphasis on freedom at the expense of both personal relationships and career security may have reflected a fear of intimacy. This is plausible, but McClintock left little of a personal nature (she destroyed nearly all of her personal letters) on which to base conclusions about the aspirations or fears that may have motivated many of her actions.

The core of the book documents McClintock's early career briefly and then her work on controlling elements in exquisite detail. Tracing her career from her training in maize cytogenetics at Cornell in the 1920s through her work on transposition in the 1940s and 1950s, Comfort convincingly shows that her work proving the existence of transposons was inspired by an interest in embryology or developmental biology rather than by an interest in the mechanisms of genetic change. For McClintock, the work was the basis for a theory that linked genetics, evolution and developmental biology, a theory that she attempted to explain to her colleagues with at best mixed success.

This insight—that McClintock was interested in the "transposition" of chromosomal elements only insofar as it could be the mechanism for development and adaptation of organisms—will surprise those familiar with McClintock's work, but it is well supported by the evidence. McClintock herself, in letters to close friends in the early 1950s, anticipated having a difficult time explaining her new work and noted that she had some trepidation about moving from the concrete experimental proofs on which she had established her career to much more speculative ideas.

Comfort has gone to great lengths to make these chapters on McClintock's experiments accessible, giving many examples to help both scientists unfamiliar with her work and lay readers to visualize her train of thought. Many readers, however, will find it difficult to follow the detailed descriptions of crosses in which she traces the behavior of the genes D, V, Ac and c-m1.

The latter part of the book describes the changing responses to McClintock's work on transposons and to her theory of development, which has never been accepted. Using extensive interviews, Comfort traces McClintock's ideas as they rippled through the fields of genetics and molecular biology and returned transformed. These chapters make for compelling reading as we follow the chance meetings, personal relationships and accidents that led to many different biological processes (including antibiotic resistance, yeast mating and cancer) being traced back to forms of "mobile DNA" and to McClintock being credited with being the first to open up this area of study.

The Tangled Field will certainly stand as the definitive work on Barbara McClintock's discovery of transposition and her ambition to explain development through controlling elements. As a biography it is less than complete: McClintock's early years at Cornell are covered only superficially, and her work in the 1960s and 1970s on the evolution of maize in the Americas receives barely a mention. However, including more on these topics might have distracted from Comfort's well-crafted argument about the transformation of McClintock's reputation, both across her career and then through successive historical interpretations.

Feminist histories of science continue to have much to say about the discrimination that forced McClintock and other women of her generation into scientific careers that were insecure and poorly paid and then frequently denied them credit for their own discoveries. But explanations of McClintock's science and career can no longer be based simply on arguments about sexism, feminine science or miscommunication. Comfort has established that it was not transposition that McClintock had in her sights but the secret to development and the unfolding of life itself.

Comfort does admirably what he set out to do—answer the many fascinating and troubling questions about McClintock's Nobel Prize–winning research, including why it took almost 40 years not to rediscover Barbara McClintock's work but to reinterpret it.—Carla C. Keirns, History and Sociology of Science, University of Pennsylvania

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