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​Barbara McClintock

· Women of value ·

“The most important thing is to develop the capacity for seeing”. With these words Barbara McClintock, an American scientist so original that she was only understood by a large part of the scientific community decades later, summed up the centrality of visual observation and of the interpretation of images for her research in genetics.

Genetics as an autonomous branch of biology was born at the beginning of the 20th century with the discovery of Mendel’s laws and was still in its first stages in 1919 when, although initially opposed by her mother who saw learning as an obstacle to marriage, Barbara enrolled in the College of Agriculture at Cornell University.

Cornell was one of the rare universities already open to women since 1872 and in 1923, the year McClintock took her degree, 74 of the 2013 science graduates were women.

Already since her very first years at university McClintock had specialized in cytology (the study of the structure and functions of cells through observation under the microscope) and had successfully applied it to the study of the genetics of maize, combining the macroscopic observation of the plant’s genetic characteristics with examination under the microscope of the physical changes in its chromosomes. She had so perfected this virtuosity in observation that illustrious colleagues turned to her for her ability to “see so much” under the microscope. This special talent stemmed from her conviction that even the smallest detail could provide the key to understanding the whole and that every organism would reveal its secrets if observed at length and with attention. For this reason she did not neglect any detail, to the point of reconstructing the whole all together in a coherent picture into which structures and functions were integrated.

This way of proceeding with method, patience and determination drove her increasingly to work by herself and she was thus considered by many to be an eccentric person.

The demonstration of crossing over (the recombination of genes through the physical exchange of information between homologous chromosomes) confirmed to her that genes are found on chromosomes; this and the discovery of chromosomal instability, were mile stones in the progress of genetics during the time she spent at Cornell.

Despite these brilliant results, in 1931 Barbara McClintock had to leave this university because of the lack of appropriate positions available to women among the staff of the faculty and her path through the university institutions was troubled indeed. In the scientific faculties women were barred from pursuing an academic career and Barbara, unlike many other women scientists, never accepted makeshift roles. In 1941 she also left the University of Missouri which had even guaranteed her a position as assistant professor, for she could not tolerate the excessive bureaucracy and the discrimination against lecturers.

This behaviour led to problems of financial insecurity and frequent changes of abode, as well as a certain reputation for eccentricity and for having a difficult character, reinforced by her unconventionality and the fact that she was not married.

This scientist’s ambitions did not include power or riches but only to be able to do research in full freedom, which she obtained by moving to the Laboratories of Cold Spring Harbor, where she could accumulate the proofs of an intuition on the presence of transposable genes in the maize genome. It took her six years of attentive observations but on the occasion of the annual symposium at Cold Spring Harbor in the summer of 1951 she presented to the scientific community the discovery of transposons, genes that could change their position by “jumping” from one part of the genome to another. Her presentation met with a stunned silence, a mixture of embarrassment, sympathy and open derision. With a few exceptions, everyone thought that this strange woman scientist was out of her mind, compounded too by the rooted mistrust of women in the academic world.

Barbara McClintock was 49 years old and in spite of the fact that her working life was punctuated by crises and precariousness, she had never lacked the recognition, esteem and support of her colleagues. Thanks also to them she had been able to confirm her position as one of America’s leading cytogeneticists.

She had in fact been appointed a member of the American Academy of Sciences in 1944, a recognition previously conferred on only two other women in this institution’s long history, and in 1945 she was the first woman President of the American Society of Human Genetics.

She was therefore shocked by the reaction of the scientific public to the point that in the following years, although she continued with determination to study the phenomenon and to accumulate proofs of it, she sought open confrontation with her colleagues on only a few other occasions, withdrawing into the shadows.

In the 1950s and 60s the numerous scientists who gathered at Cold Spring Harbor every summer to discuss and to share the most recent scientific breakthroughs were not unaware of the anomalous presence, almost set aside, of a minute, agile woman with a lively expression, dressed without any affectation in work trousers and a tee shirt, whom it was possible to meet on her comings and goings between the laboratory and the maize fields or during her solitary walks in the woods or on the beach.

This woman was Barbara McClintock who, having contributed to the development of classical genetics with work of fundamental importance, seemed to have been completely eclipsed, as if she were almost a useless legacy of the past.

Although she had stepped back, she took part as an attentive listener in scientific debates and gladly opened the doors of her laboratory to anyone interested; however the scientists who requested a conversation with her were few and rarely well disposed.

One of the reasons for the incomprehension of the scientific community was certainly the fact that the discovery of “jumping genes” appeared to be going against the tide of what were then the theoretical pillars of genetics. McClintock’s discovery in fact contradicted the simple rules of Mendel and conflicted with the mechanism of spontaneous mutation as a vehicle of evolution on the basis of Neo-Darwinism.

In those days the structure of the genome was considered to be absolutely static and the information unidirectional from the dna to the cell. Thus almost no one thought it plausible that genes could move and even less that this movement was programmed and controlled by other genes in response to external signals to the genome itself; nor was it deemed possible that, by changing their positions, genes might express new functions.

Moreover McClintock’s language proved obscure, “mystical”, unacceptable at a time when the successes of molecular biology (including the discovery of the structure of dna in 1953) were profoundly changing the manner of carrying out research and of explaining biological phenomena.

Barbara McClintock was unable to explain transposition in the terms of molecular biology and this prevented her from communicating her results in the form required by the new biology and relegated her to marginality.

Curiously, the rediscovery of transposons and the explanation of the mechanism of movement were to come from molecular genetics. From the middle of the 1960s proofs of the plasticity of the genome began to accumulate and, in the second half of the 1960s the mechanism described by McClintock was expressed in the terms of molecular genetics, accessible to the general comprehension. The reevaluation of this woman scholar revealed the value and importance of her discovery to the point that she was awarded the Nobel Prize for Medicine in 1983, a good 35 years after the first publication of her work on transposons.

The delay in recognition was undoubtedly due to the revolutionary character of the discovery, but also to the particular manner with which McClintock arrived at her knowledge and understanding of the phenomena. As was noted at the beginning of this article, she was convinced that every organism would reveal its secrets if observed for a long time, attentively and in minute detail. Through this long practice in visual observation she had managed to construct a mental image of the world that was hard to communicate since it was strictly subjective.

For everyone vision of the natural world is based on observation, but what we see is closely linked to what we know: the more we know, the more we see. This relationship between visual and cognitive processes is, however a double-edged sword since the baggage of acquired knowledge can hinder the understanding of phenomena which lie outside consolidated mental patterns. For Barbara McClintock this reciprocity seems instead to have been particularly intense and fertile.

Maria Balduzzi

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