W.H. Freeman & Co., 1983
? 1983 by W.H. Freeman & Company. Used with permission. All rights reserved.

In her mid-thirties, Barbara McClintock's particular scientific style was already well defined and emerging in ever-sharper relief. Its distinctive features were polar in character: its ultimate strength derived from a dialectic between two opposing tendencies. The reader may recall from the previous chapter a characterization of her work by Morgan as "highly specialized." And, although few would accept Morgan's description of the cytology of maize genetics as any more narrow a category than the cytology of Drosophila genetics, one aspect of McClintock's scientific preoccupations may easily have led him to such a description :her focus on the minutest of details. The tenacity with which she hunted down every observable chromosomal modification, the thoroughness and rigor that accompanied her virtuoso technique - all these might lead one to think of the focus of her search as narrow. In fact, what she consistently pursued was nothing less than an understanding of the entire organism.

The word "understanding," and the particular meaning she attributed to it, is the cornerstone of Barbara McClintock's entire approach to science. For her, the smallest details provided the keys to the larger whole. It was her conviction that the closer her focus, the greater her attention to individual detail, to the unique characteristics of a single plant, of a single kernel, of a single chromosome; the more she could learn about the general principles by which the maize plant as a whole was organized, the better her "feeling for the organism."

To some extent the stories she tells to illustrate the meaning of "understanding" recall what might be called the "naturalist" tradition - a tradition that in most parts of biology had long been replaced by the experimental tradition, but traces of which nevertheless still survived in the mid-1930s. McClintock was able to incorporate and integrate these traces into an otherwise thoroughly experimental stance. No scientist ever develops in a vacuum, but it is difficult to find any direct intellectual influences that can be held responsible for this element in her thought. Rather, it would seem that she came to this amalgam in her own highly individualistic way, dictated more by internal forces than by external ones. The stories themselves reflect this.

She describes, for example, an experience from her early days at Missouri when she was pursuing some elaborations of the ring chromosome motif.

Most of the time, ring chromosomes undergo semiconservative replication, but there are occasional sister strand exchanges which will produce a double-size ring, having two centromeres. At anaphase, [the two centromeres] start to go to opposite poles, but [since] it's a double size ring, it breaks. It breaks in different places, and the broken ends fuse to form new rings - different from the old. If they are small, they will frequently get lost - they will not make the telophase. Among the plants that were growing in the culture I was dealing with, there were those that could have one, two, or three of these rings, in any combination. One ring might be small; the other two could be a bit larger. In these plants, the ring chromosomes carried the dominant genes, and in order to get the recessive expression, the ring carrying the gene would have to get lost.

So adept did she become at recognizing the outward signs of those structural alterations in chromosomal composition that she could simply look at the plants themselves and know what the microscopic inspection of the cells' nuclei would later reveal.

Before examining the chromosomes, I went through the field and made my guess for every plant as to what kind of rings it would have - would it have one, two, or three, small or large, which combination? And I never made a mistake, except once. When I examined that one plant I was in agony. I raced right down to the field. It was wrong; it didn't say what the notebook said it should be! I found that . . . I had written the number from the plant adjacent, which I had not cut open. And then everything was all right.

Her belief is that the mind functions "like a computer" - processing and integrating data far more complex than we can possibly be conscious of. And finding the cause of her mistake - a misfiling error, as it were - was reassuring. "That made me feel perfect, because it showed me that whatever this computer was doing, it was doing it right." All she was conscious of doing was "looking at these fine stripes of recessive tissue"; she says the computer did the rest. "And I never made a mistake." The crucial point of this story, to her, is the state of mind required in making such judgments. "It is done with complete confidence, complete understanding. I understood every plant. Without being able to know what it was I was integrating, I understood the phenotype." What does understanding mean here? "It means that I was using a computer that was working very rapidly and very perfectly. I couldn't train anyone to do that."

Since her days as a young graduate student, she had always carried out the most laborious parts of her investigations herself, leaving none of the labor, however onerous or routine, to others. In this she did as almost all beginning scientists do. But most scientists, as they mature, learn to delegate more and more of the routine work to others. There are, of course, exceptions, and Emerson, who, according to Harriet Creighton, "didn't regard anything as routine," was one. He prided himself on doing his own work. For McClintock, more than pride was involved. Her virtuosity resided in her capacity to observe, and to process and interpret what she observed. As she grew older, it became less and less possible to delegate any part of her work; she was developing skills that she could hardly identify herself, much less impart to others.

The nature of insight in science, as elsewhere, is notoriously elusive. And almost all great scientists - those who learn to cultivate insight - learn also to respect its mysterious workings. It is here that their rationality finds its own limits. In defying rational explanation, the process of creative insight inspires awe in those who experience it. They come to know, trust, and value it.

When you suddenly see the problem, something happens that you have the answer - before you are able to put it into words. It is all done subconsciously. This has happened too many times to me, and I know when to take it seriously. I'm so absolutely sure. I don't talk about it, I don't have to tell anybody about it, I'm just sure this is it.

This confidence was not new. She tells of an occasion from her early days at Cornell - another instance in which "understanding" seemed to bypass any conscious awareness: "A particular plant was heterozygous with respect to a translocation; that is, one chromosome carried the translocation, while the homologous chromosome was normal. According to meiotic segregation, it would normally give pollen grains which would be 50 percent defective [hence sterile] and SO percent normal. We had at that time a postdoc who had just started working with translocations. He was examining pollen from these plants, expecting them to be either perfect [having no translocations] or to be heterozygous [where 50 percent of the pollen would be sterile]. He came to me and said, 'There are some plants that are 25 to 30 percent sterile, not 50 percent sterile.' He told me this in the field and he was disturbed." McClintock was disturbed too - so much so that she left the field, down in the hollow, and walked up to her laboratory. There she sat for about thirty minutes,

just thinking about it, and suddenly I jumped up and ran down to the field. At the top of the field (everyone else was down at the bottom) I shouted, 'Eureka, I have it! I have the answer! I know what this 30 percent sterility is.'" When she got to the bottom of the hollow, the group of corn geneticists working there gathered around her, and she realized she couldn't provide the reasoning behind her insight. "Prove it," they said. "I sat down with a paper bag and a pencil and I started from scratch, which I had not done at all in my laboratory. It had all been done fast; the answer came, and I'd run. Now I worked it out step by step - it was an intricate series of steps - and I came out with what it was. [The postdoc] looked at the material and it was exactly as I'd said it was, and it worked exactly as I'd diagrammed it. Now, why did I know, without having done a thing on paper? Why was I so sure that I could tell them with such excitement and just say, 'Eureka, I solved it!'?

Perhaps the answer, once again, depends on the intimate and total knowledge she sought about each and every plant. A colleague once remarked that she could write the "autobiography" of each plant she worked with. Her respect for the unfathomable workings of the mind was matched by her regard for the complex workings of the plant, but she was confident that, with due attentiveness, she could trust the intuitions the one produced of the other. In the years to come, that confidence would become a source of vital sustenance.

Evelyn Fox Keller is Professor of History and Philosophy in the Program in Science, Technology, and Society at M.I.T. Her achievements include a MacArthur Foundation Fellowship and an honorary degree from the University of Amsterdam. Dr. Keller is known both for her scholarship on twentieth-century biology and her work on gender and science.

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