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ON THE ABSENCE OF REVOLUTIONS IN BIOLOGY LEONARD HERSHER* In 1962, Thomas S. Kuhn surprised and delighted the intellectual world with a treatise on the nature of scientific revolutions—novel, extraordinary perceptions of reality that radically changed the understanding of nature and ultimately led to the advance of science [I]. Kuhn, trained as a theoretical physicist before his studies in scientific history, limited his examples of revolutions to astronomy, physics, and chemistry, although he felt that "Far more historical evidence is available than I have had space to exploit below. Furthermore, that evidence comes from the history of biological as well as of physical science. My decision to deal here exclusively with the latter was made partly to increase this essay's coherence and partly on grounds of present competence " [1, p. ix]. However, in the second edition of his work, The Structure of Scientific Revolutions, published in 1970, and in a later book, The Essential Tension (1977), Kuhn again failed to give examples of biological revolutions. In 1977 he wrote, "Omitting the biological sciences, for which close ties to medieval crafts and institutions dictate a more complex developmental pattern, the main branches of science transformed during the 16th and 17th centuries were astronomy, mathematics, mechanics and optics" [2, p. 117]. To my knowledge, Kuhn has not yet tackled biology, 25 years after he first discussed the importance of investigating and using examples of revolutions in the science of life. Furthermore, probably the most comprehensive recent discussion of significant changes in the history of science , Revolution in Science, by J. Bernard Cohen [3], touches, like Kuhn, only peripherally on radical changes in biology. Kuhn's essay on revolutions in science argues, in brief: (1) Observation, conjecture-logic, and experiment result in the development of a "paradigm." Subsequent work all falls under the rubric of ?Department of Pediatrics, State University of New York Health Science Center, 750 East Adams Street, Syracuse, New York 13210.© 1988 by The University of Chicago. All rights reserved. 0031-5982/88/3103-0583$01.00 318 I Leonard Hersher ¦ Revolutions in Biology this paradigm, filling in empty spaces and elaborating it. Such work is "normal science." (2) Eventually, "anomalies"—observations that contradict the paradigm—appear. (3) They are explained in terms of normal science until the weight of the contradictions culminate in a "crisis." (4) Eventually, a new paradigm replaces the old, and a new normal science develops. One of Kuhn's examples is the phlogiston theory ofcombustion. Commonsense observation made it appear that substances were released during burning; weighing wood ashes demonstrated that the ash weighed less than the unburned wood. Scientists before Lavoisier, however, also noted that some roasted metals weighed more after roasting, and new techniques of collecting gases showed that even the total product of burned wood was heavier than the original log. Although many attempts to explain the weight increase (phlogiston had negative weight, e.g.) were made, eventually the idea was accepted that, in burning, something (oxygen, a pungent gas isolated from ordinary air) was added. A new paradigm replaced the old. The new paradigm for combustion was the reverse of the old; similarly, Kuhn argues, all new paradigms are perceptual reversals, a phenomenon that occurs, for example, when a line is first interpreted as the edge of a figure and later as the edge of the background of the figure. Why have Kuhn, his students, or Cohen failed to fulfill the promise to discuss revolutions in biology? Certainly, 25 years is long enough for Kuhn to have become "competent" in the life sciences. It seems more likely that science historians of a Kuhnian bent simply gave up in despair . Kuhnian revolutions do not occur in biology. William Harvey and the Circulation ofBlood The major paradigm before William Harvey, describing the flow of blood through the body, was the system proclaimed by Galen, an explanation that went unchallenged for more than a thousand years. It originated with Aristotle, was modified by the Alexandrian physicians Erasistratus and Herophilus, and was changed and organized by Galen, father of medicine. Galen wrote that food was brought from the stomach and intestines through veins to the liver, where the blood was formed. Veins then...


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