[ernst_mayr]_the_growth_of_biological_thought_div.pdf

8/17/2019 [Ernst_Mayr]_The_Growth_of_Biological_Thought_Div.pdf

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The Growth of Biological Thought

Diversity, Evolution, and Inheritance

ERNST MAYR

The Belknap Press of Harvard University Press Cambridge,Massachusetts London, England


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Copyright © 1982 by Ernst Mayr All rights reserved Printed in the United States

of AmericaEleventh printing, 2000Library of Congress Cataloging in Publication Data

Mayr, Ernst, 1904The growth of biological thought.Bibliography: p. Includes index. 1. Biology ― History. 2. Biology ―

Philosophy ― History. I. Title.QH305.M26 574'.09 81-13204

ISBN 0-674-36445-7 (cloth) AACR2

ISBN 0-674-36446-5 (paper)


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For Gretel


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Preface

MUCH OF MODERN BIOLOGY, particularly the variouscontroversies between different schools of thought, cannot be fullyunderstood without a knowledge of the historical background of the problems. Whenever I made this point to my students, they would ask me inwhat book they could read up on these matters. To my embarrassment, I hadto admit that none of the published volumes filled this need. To be sure,there is much literature on the lives of biologists and their discoveries, butthese writings are invariably inadequate as far as an analysis of the major problems of biology are concerned or as a history of concepts and ideas in biology. While some of the histories of individual biological disciplines,like genetics and physiology, are indeed histories of ideas, there is nothingavailable that covers biology as a whole. To fill this gap in the literature isthe object of this work. This volume is not, and this must be stressed, ahistory of biology, and it is not intended to displace existing histories of biology, such as that of Nordenskiöld. The emphasis is on the backgroundand the development of the ideas dominating modern biology; in otherwords, it is a developmental, not a purely descriptive, history. Such atreatment justifies, indeed necessitates, the neglect of certain temporarydevelopments in biology that left no impact on the subsequent history ofideas.

When I first conceived the plan to write a history of ideas in biology,the goal seemed impossibly remote. The first years (19701975) weredevoted to reading, notetaking, and the preparation of a first draft. Soon it became obvious that the subject was too vast for a single volume, and Idecided to prepare first a volume on the biology of "ultimate" (evolutionary)causations. But even this limited objective is a hopelessly vast undertaking.If I have been successful at all, it is because I have myself done aconsiderable amount of research in most areas covered by this volume. Thismeans that I was already reasonably familiar with the problems and some ofthe literature of the areas involved. I hope to

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deal with the biology of "proximate" (functional) causations in a latervolume that will cover physiology in all of its aspects, developmental biology, and neurobiology. When a biological discipline, for instancegenetics, deals both with ultimate and proximate causations, only the

ultimate causations are treated in the present volume. There are two areas of biology that might have been (at least in part) but were not included in thisvolume: the conceptual history of ecology and that of behavioral biology(particularly ethology). Fortunately, this omission will not be quite as painful as it might otherwise be, because several volumes by other authorsdealing with the history of ecology and ethology are now in active preparation.

The professional historian is not likely to learn much from chapters 1

and 3; in fact he may consider them somewhat amateurish. I have addedthese two chapters for the benefit of nonhistorians, believing that it will helpthem to see the purely scientific developments of the other chapters with adeepened perception.

I owe an immense debt of gratitude to numerous individuals andinstitutions. Peter Ashlock, F. J. Ayala, John Beatty, Walter Bock, RobertBrandon, Arthur Cain, Fred Churchill, Bill Coleman, Lindley Darden, MaxDelbrück, Michael Ghiselin, John Greene, Carl Gustav Hempel, Sandra

Herbert, Jon Hodge, David Hull, David Layzer, E. B. Lewis, RobertMerton, J. A. Moore, Ron Munson, Edward Reed, Phillip Sloan, FrankSulloway, Mary Williams, and others have read drafts of various chapters,have pointed out errors and omissions, and have made numerousconstructive suggestions. I did not always follow their advice and am thussolely responsible for remaining errors and deficiencies. To P. Ax, MurielBlaisdell, and B. Werner I am indebted for useful factual information.

Gillian Brown, Cheryl Burgdorf, Sally Loth, Agnes I. Martin,

Maureen Sepkoski, and Charlotte Ward have typed innumerable drafts andhelped with the bibliography. Walter Borawski not only typed preliminaryversions but also the entire final copy of the manuscript and of the bibliography and prepared the manuscript of the index. Randy Birdcontributed to filling gaps in the references. Susan Wallace edited the entiremanuscript and in the process eliminated numerous inconsistencies,redundancies, and stylistic infelicities. All of these people materiallycontributed to the quality of the final product. It is obvious how great a debt

of gratitude I owe to them. -viii-


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The Museum of Comparative Zoology, through the courtesy of itsDirector, Professor A. W. Crompton, has provided office space, secretarialhelp, and library facilities, even after my retirement. Research periods at theI nstitute for Advanced Study (Princeton, spring 1970), at the library of the

Max Planck Institute of Biology (Tfibingen, 1970), a senior fellowship ofthe Alexander von Humboldt Foundation (Würzburg, 1977), a fellowshipawarded by the Rockefeller Foundation (Villa Serbelloni, Bellagio, 1977),and a grant (No. GS 32176) by the National Science Foundation havegreatly facilitated my work.

Whenever secretarial help was not available, my wife took over,transcribed dictations, excerpted literature, and aided the work on themanuscript in countless ways. It is impossible to acknowledge appropriately

her inestimable contributions to this volume.Ernst Mayr Museum of Comparative Zoology Harvard University

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Contents

1 Introduction: How to write history of biology 1

Subjectivity and bias 9Why study the history of biology? 182 The place of biology in the sciences and its conceptual structure 21

The nature of science 21

Method in science 25The position of biology within the sciences 32How and why is biology different? 36Special characteristics of living organisms 51Reduction and biology 59Emergence 63The conceptual structure of biology 67A new philosophy of biology 733 The changing intellectual milieu of biology 83

Antiquity 84The Christian world picture 91The Renaissance 94The discovery of diversity 99Biology in the Enlightenment 107The rise of science from the seventeenth to the nineteenth century 109Divisive developments in the nineteenth century 112Biology in the twentieth century 120Major periods in the history of biology 125Biology and philosophy 128

Biology today 131

Part I Diversity of Life

4 Macrotaxonomy, the science of classifying 147

Aristotle 149The classification of plants by the ancients and the herbalists 154Downward classification by logical division 158Pre-Linnaean zoologists 166

Carl Linnaeus 171Buffon 180A new start in animal classification 182

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Taxonomlc characters 185Upward classification by empirical grouping 190Transition period (1758-1859) 195Hierarchical classifications 2055 Grouping according to common ancestry 209

The decline of macrotaxonomic research 217 Numerical phenetics 221Cladistics 226The traditional or evolutionary methodology 233

New taxonomic characters 235Facilitation ofinformation retrieval 239The study of diversity 2456 Microtaxonomy, the science of species 251

Early species concepts 254

The essentialist species concept 256The nominalistic species concept 263Darwin's species concept 265The rise of the biological species concept 270Applying the biological species concept to multidimensional species taxa 286The eignificance of species in biology 295

Part II Evolution

7 Origins without evolution 301The coming of evolutionism 309The French Enlightenment 3228 Evolution before Darwin 343

Lamarck 343Cuvier 363England 371Lyell and uniformitarianism 375Germany 3879 Charles Darwin 394

Darwin and evolution 400Alfred Russel Wallace 417The publication of the Origin 42310 Darwin's evidence for evolution and common descent 426

Common descent and the natural system 436Common descent and geographical distribution 439Morphology as evidence for evolution and common descent 455Embryology as evidence for evolution and common descent 46911 The causation of evolution: natural selection 477

The major components of the theory of natural selection 481The origin of the concept of natural selection 488The impact of the Darwinian revolution 501

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The resistance to natural selection 510Alternate evolutionary theories 52512 Diversity and synthesis of evolutionary thought 535

The growing split among the evolutionists 540Advances in evolutionary genetics 550

Advances in evolutionary systematics 559The Levolutionary synthesis 56613 Post-synthesis developments 571

Molecular biology 574 Natural selection 585Unresolved issues in natural selection 591Modes of speciation 600Macroevolution 607The evolution of man 620Evolution in modern thought 626

Part III Variation and Its Inheritance

14 Early theories and breeding experiments 633

Theories of inheritance among the ancients 635Mendel's forerunners 64115 Germ cells, vehicles of heredity 652

The Schwann-Schleiden cell theory 655The meaning of sex and fertilization 658

Chromosomes and their role 67316 The nature of inheritance 681

Darwin and variation 681August Weismann 698Hugo de Vries 707Gregor Mendel 71017 The flowering of Mendelian genetics 727

The rediscoverers of Mendel 727The classical period of Mendelian genetics 731The origin of new variation (mutation) 738The emergence of modern genetics 744The Sutton-Boveri chromosome theory 747Sex determination 750Morgan and the fly room 752Meiosis 761Morgan and the chromosome theory 76918 Theories of the gene 777

Competing theories of inheritance 784The Mendelian explanation of continuous variation 790

19 The chemical basis of inheritance 808

The discovery of the double helix 821Genetics in modern thought 826

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20 Epilogue: Toward a science of science 829

Scientists and the scientific milieu 830The maturation of theories and concepts 839Impediments to the maturation of theories and concepts 843The sciences and the external milieu 848

Progress in science 856

Notes 861

References 893

Glossary 957

Index 961

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The Growth of Biological Thought


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1 Introduction: How to write history of biology

ANYTHING THAT changes in time has, by definition, a history ― theuniverse, countries, dynasties, art and philosophy, and ideas. Science also,ever since its emergence from myths and early philosophies, has experienced a

steady historical change and is thus a legitimate subject for the historian.Because the essence of science is the continuing process of problem solving inthe quest for an understanding of the world in which we live, a history ofscience is first a history of the problems of science and their solution orattempted solutions. But it is also a history of the development of the principles that form the conceptual framework of science. Because the greatcontroversies of the past often reach into modern science, many currentarguments cannot be fully understood unless one understands their history.

Written histories, like science itself, are constantly in need of revision.Erroneous interpretations of an earlier author eventually become myths,accepted without question and carried forward from generation to generation.A particular endeavor of mine has been to expose and eliminate as many ofthese myths as possiblewithout, I hope, creating too many new ones. The mainreason, however, why histories are in constant need of revision is that at anygiven time they merely reflect the present state of understanding; they dependon how the author interpreted the current zeitgeist of biology and on his ownconceptual framework and background. Thus, by necessity the writing ofhistory is subjective and ephemeral. 1

When we compare published histories of science, it becomes at onceapparent that different historians have quite different concepts of science andalso of history writing. Ultimately all of them attempt to portray the increase inscientific knowledge and the changes in interpretive concepts. But not allhistorians of science have attempted to answer the six principal questions thatmust be addressed by anyone who wants to describe the progress of sciencecritically and comprehensively: Who? When? Where?

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What? How? and Why? On the basis of the author's selection from amongthese questions, most of the histories known to me can be classified as follows(cf. Passmore, 1965: 857-861), though it must be recognized that nearly allhistories are a combination of the various approaches or strategies:

Lexicographic Histories

These are more or less descriptive histories with a strong emphasis onthe questions What? When? and Where? What were the principal scientificactivities at any given past period? What were the centers of science where theleading scientists were working, and how did they shift in the course of time? No one will argue about the value of such histories. A correct presentation ofthe true facts is indispensable because much of the traditional history ofscience (and its standard texts) is encrusted with myths and spurious

anecdotes. Yet, a purely descriptive history provides only part of the story.Chronological Histories

A consideration of time sequences is crucial to any kind of historywriting. Indeed, one can even make chronology the primary organizingcriterion, and some authors have done so. They have asked, for instance, whathappened in biology between 1749 and 1789, or between 1789 and 1830?Chronological histories present a sequence of cross sections through the

entirety of developments in all branches of biology. This is not only alegitimate but indeed a most revealing approach. It creates a feeling for thezeitgeist and the totality of contemporary influences. It permits one toinvestigate how developments in other branches of science have influenced biology, and how even within biology advances made by the experimentalistshave affected the thinking of the naturalists, and vice versa. The understandingof many problems in the development of biology is greatly facilitated by thischronological approach. However, it suffers from the drawback that eachmajor scientific problem is atomized.

Biographical Histories

The endeavor in these volumes is to portray the progress of sciencethrough the lives of leading scientists. This approach is also legitimate, sincescience is made by people and the impact of individual scientists like Newton,Darwin, and Mendel has often been of quasi-revolutionary nature. However,this approach shares

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with the purely chronological approach one very serious weakness: it atomizeseach major scientific problem. The species problem, for example, will have to be discussed under Plato, Aristotle, Cesalpino and the herbalists, Buffon,Linnaeus, Cuvier, Darwin, Weismann, Nägeli, de Vries, Jordan, Morgan,Huxley, Mayr, Simpson, and so on. All of these discussions of the same problem are separated from each other by many pages, if not chapters.

Cultural and Sociological Histories

This approach stresses the point that science is a form of humanendeavor and is therefore inseparable from the intellectual and institutionalmilieu of the period. This view is particularly fascinating to those who come tothe history of science from the field of general history. They might ask suchquestions as why was British science from 1700 to 1850 so strongly

experimental and mechanical while contemporary French science tended to bemathematical and rationalistic? Why did natural theology dominate sciencefor 75 years longer in Britain than on the continent? To what extent wasDarwin's theory of natural selection a child of the industrial revolution?

Even if the historian of biology chooses not to adopt this approach, hemust carefully study the cultural and intellectual milieu of a scientist if hewants to determine the causes for the rise of new concepts. This is of evidentimportance in the present work, since one of the major objectives of my

treatment is to investigate the reasons for the changes in biological theories.What enabled one investigator to make a discovery that has escaped hiscontemporaries? Why did he reject the traditional interpretations and advancea new one? From where did he get the inspiration for his new approach? Theseare the kind of questions that need to be asked.

Most early histories of science, particularly those of special scientificdisciplines, were written by working scientists, who took it for granted that theintellectual impetus for scientific change came from within the field itself

("internal" influences). Later on, when the history of science became more professionalized and historians and sociologists began to analyze the progressof scientific thought, they tended to stress the influence of the generalintellectual, cultural, and social milieu of the period ("external" influences). No one would want to doubt that both kinds of influences exist, but there is agreat deal of disagreement on their rel-

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ative importance, particularly with reference to specific developments, such asDarwin's theory of natural selection.

Often it is rather difficult even to distinguish external from internalfactors. The Great Chain of Being (scala naturae) was a philosophical concept

which clearly had an impact on concept formation in the case of Lamarck andother early evolutionists. Yet, Aristotle had developed this concept on the basis of empirical observations of organisms. On the other hand, universallyadopted ideologies are among the most uncontroversial of external factors.The Christian dogma of creationism and the argument from design comingfrom natural theology dominated biological thinking for centuries.Essentialism (from Plato) is another all-powerful ideology. Interestingly, itsdisplacement by Darwin was largely due to the observations of animal breeders and taxonomists-that is, to internal factors.

External factors do not necessarily originate in religion, philosophy,cultural life or politics, but ― as far as biology is concerned ― they mayoriginate in a different science. The extreme physicalism (includingdeterminism and extreme reductionism) that was prevalent in Westernthinking after the scientific revolution strongly influenced theory formation in biology for several centuries, often quite adversely as is now evident.Scholastic logic, to cite another example, dominated taxonomic method fromCesalpino to Linnaeus. These examples, to which many others could be added,

document without doubt the importance of external influences on theoryformation in biology. They will be analyzed in full detail in the relevantchapters.

It is important to realize that external factors influence science in twoentirely different ways: They may either affect the overall level of scientificactivity at a given place at a given time, or they may affect or even give rise toa particular scientific theory. All too often in the past these two aspects have been lumped together, resulting in much controversy over the relative

importance of external versus internal factors.The effect of environmental conditions on the level of scientific

activities has been appreciated as long as there has been a history of science. Ithas been speculated endlessly as to why the Greeks had such an interest inscientific questions and why there was a revival of science during theRenaissance. What was the effect of Protestantism on science (Merton, 1938)?Why did science during the nineteenth century flourish to such an extent inGermany? Sometimes important external factors can be specified,

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for instance (as Merz, 1896-1914, has pointed out), the replacement in 1694 ofLatin by German at Halle University, and the founding in 1737 of a Universityat Göttingen in which "Wissenschaft" played an important role. Institutionalchanges of all sorts, including the founding of the Royal Society, politicalevents such as wars and the launching of Sputnick, as well as technologicalneeds have had either a stimulating or a depressing effect on the level ofscientific activity. Yet, this still leaves open the highly controversial questionof to what extent such external factors have favored or inhibited specific scientific theories.

In recent years Marxist historiographers in particular have voiced thethesis that social ideologies influence the ideas of a scientist, and that thehistory of science as practiced until now has totally neglected the socialcontext. The result, they believe, has been a bourgeois history of science,

which is quite different from what a proletarian history of science would be.What is needed instead, they say, is "radical" history. This demand ultimatelygoes back to Marx's claim that ruling ideas cannot be separated from rulingclasses. Therefore, bourgeois history of science will be quite different from proletarian history of science.

However, the thesis that there is a proletarian way to write the history ofscience is in conflict with three sets of facts: First, the masses do not establishscientific theories that are different from those of the scientific class. If there is

any difference, it is that the "common man" often retains ideas long after theyhave been discarded by scientists. Second, there is high social mobility amongscientists, with from one quarter to one third of each new crop of scientistscoming from the lower socioeconomic classes. Third, birth order within asocial class tends to be far more important in determining those who originaterebellious new ideas than does membership in a particular class (Sulloway,MS). All of this is in conflict with the thesis that the socioeconomicenvironment has a dominant impact on the birth of particular new scientific

ideas and concepts. The burden of proof is clearly on those who make suchclaims, and so far they have failed to supply any concrete evidence whatsoever(see Chapter 11).

Of course no one lives in a vacuum, and anyone who reads voraciously,as for example Darwin did after his return from the voyage of the Beagle, is bound to be influenced by his reading (Schweber, 1977). Darwin's notebooksare ample evidence for the correctness of this inference. But, as Hodge (1974) points out, this by itself does not prove the thesis of the Marxists that "Darwin

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and Wallace were extending the laissez-faire capitalist ethos from society toall nature." Up to now it appears that the influence of social factors on thedevelopment of specific biological advances has been negligible. The reverse,

of course, is not true. But the study of the impact of science on social theory,social institutions, and politics belongs to the domains of history, sociology,and political science, and not to that of the history of science. I agree withAlexander Koyré (1965: 856) that it is futile to "deduce the existence" ofcertain scientists and sciences from their environment. "Athens does notexplain Plato anymore than Syracuse explains Archimedes or FlorenceGalileo. To look for explanations along these lines is an entirely futileenterprise, as futile as trying to predict the future evolution of science or of thesciences as a function of the structure of the social context." Thomas Kuhn

(1971: 280) has likewise observed that the historian seems invariably to give"excessive emphasis to the role of the surrounding climate of extra-scientificideas" (see also Passmore, 1965).

Problematic Histories

More than one hundred years ago Lord Acton advised historians,"Study problems, not periods." This advice is particularly appropriate for thehistory of biology, which is characterized by the longevity of its scientific

problems. Most of the great controversies of the nineteenth and early twentiethcenturies relate to problems already known to Aristotle. Such controversiesendure from generation to generation, and from century to century. They are processes, not events, and can be fully understood only through a historicaltreatment. As R. G. Collingwood said of history (1939: 98), it "is concernednot with events but with processes. Processes are things which do not beginand end but turn into one another." This must be stressed particularly in theface of the static views of the logical positivists who thought that logicalstructure was the real problem of science: "The philosophy of science isconceived [by them] primarily as a careful and detailed analysis of the logicalstructure and the conceptual problems of contemporary science" (Laudan,1968). Actually most scientific problems are far better understood by studyingtheir history than their logic. However, it must be remembered that problematic history does not replace chronological history. The twoapproaches are complementary.

In the problematic approach the chief emphasis is placed on the historyof attempts to solve problems ― for instance, the nature

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of fertilization or the direction-giving factor in evolution. The history not onlyof the successful but also of the unsuccessful attempts to solve these problemsis presented. In the treatment of the major controversies in the field, anendeavor is made to analyze the ideologies (or dogmas) as well as the particular evidence by which the adversaries supported their opposingtheories. In problematic history the emphasis is on the working scientist andhis conceptual world. What were the scientific problems of his time? Whatwere the conceptual and technical tools available to him in his quest for asolution? What were the methods he could employ? What prevalent ideas ofhis period directed his research and influenced his decisions? Questions of thisnature dominate the approach in problematic history.

I have chosen this approach for the present book. The reader should beaware of the fact that this is not a traditional history of science. Owing to its

concentration on the history of scientific problems and concepts, it slights bynecessity the biographical and sociological aspects of the history of biology. Itshould therefore be used in conjunction with a general history of biology (like Nor denskiöld, 1926), with the Dictionary qf Scientific Biography, and withavailable histories of special areas of biology. Since I am a biologist, I am better qualified to write a history of the problems and concepts of biology thana biographical or sociological history.

It is the essence of problematic history to ask why. Why was it in

England that the theory of natural selection was developed, in factindependently four times? Why did genuine population genetics arise inRussia? Why were Bateson's explanatory attempts in genetics almostuniformly wrong? Why did Correns get distracted into all sorts of peripheral problems and therefore contributed so little to major advances in genetics after1900? Why did the Morgan school devote their efforts for so many years toreinforcing the already well-established chromosome theory of inheritance,instead of opening up new frontiers? Why were de Vries and Johannsen so

much less successful in the evolutionary application of their findings than intheir straight genetic work? Attempts to answer such questions require thecollecting and scrutiny of much evidence, and this almost invariably leads tonew insights even if the respective question turns out to have been invalid.Answers to why-questions are inevitably somewhat speculative andsubjective, but they force one into the ordering of observations and into theconstant testing of one's conclusions consistent with thehypothetico-deductive method. Now that the

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legitimacy of why-questions has been established even for scientific research, particularly in evolutionary biology, there should be even less question aboutthe legitimacy of such questions in the writing of history. At the worst, thedetailed analysis necessitated by such a question may establish that theassumptions underlying the question were wrong. Even this would advanceour understanding.

Throughout this volume I have endeavored to carry the analysis of each problem as far as possible and to dissect heterogeneous theories and conceptsinto their individual components. Not all historians have been aware howcomplex many biological concepts are ― in fact, how complex the structure of biology as a whole is. As a consequence, some exceedingly confused accountsof the history of biology have been published by authors who did notunderstand that there are two biologies, that of functional and that of

evolutionary causations. Similarly, anyone who writes about "Darwin's theoryof evolution" in the singular, without segregating the theories of gradualevolution, common descent, speciation, and the mechanism of naturalselection, will be quite unable to discuss the subject competently. Most majortheories of biology were, when first proposed, such composites. Their historyand their impact cannot be understood unless the various components areseparated and studied independently. They often belong to very differentconceptual lineages.

It is my conviction that one cannot understand the growth of biologicalthought unless one understands the thought-structure of biology. For thisreason I have attempted to present the insights and concepts of biology inconsiderable detail. This was particularly necessary in the treatment ofdiversity (Part I) because no other adequate treatment or conceptualframework of the science of diversity is available. I am aware of the dangerthat some critic might exclaim, "But this is a textbook of biology, historicallyarranged!" Perhaps this is what a problematical history of biology ought to be.

Perhaps the greatest difficulty any conceptual history of biology must copewith is the longevity of the controversies. Many of the current controversieshad their origin generations or even centuries ago, some indeed going all theway back to the Greeks. A more or less "timeless" presentation of the issues ismore constructive in such cases than a chronological one.

I have tried to make each of the major sections of this volume(Diversity, Evolution, Inheritance) a self-contained unit. A similar separationis attempted for each separate problem within these

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three major areas. This leads to a certain amount of overlap and redundancy because there are numerous cross-connections between different topics andeach topical strand will pass through the same sequence of time-dependentintellectual milieus. I have made a special effort to strike a balance between acertain amount of unavoidable duplication and convenient cross references toother chapters.

Subjectivity and Bias

A well-known Soviet theoretician of Marxism has once referred to mywritings as "pure dialectical materialism." I am not a Marxist and I do notknow the latest definition of dialectical materialism, but I do admit that I sharesome of Engels' antireductionist views, as stated in his Anti-Dühring, and that Iam greatly attracted by Hegel's scheme of thesis-antithesis-synthesis.

Furthermore, I believe that an antithesis is most easily provoked by acategorical statement of a thesis, and that the issue is most readily resolved bysuch a confrontation of an uncompromising thesis and antithesis and that theultimate synthesis is thus most quickly achieved. Many examples for this can be found in the history of biology.

This view has dominated my presentation. Whenever possible, I haveattempted a synthesis of opposing viewpoints (unless one of them is clearly inerror). Where the situation is quite unresolved, I have described the opposing

viewpoints in categorical, sometimes almost one-sided, terms in order to provoke a rejoinder, if such is justified. Because I hate beating around the bush, I have sometimes been called dogmatic. I think this is the wrong epithetfor my attitude. A dogmatic person insists on being right, regardless ofopposing evidence. This has never been my attitude and, indeed, I pride myselfon having changed my mind on frequent occasions. However, it is true that mytactic is to make sweeping categorical statements. Whether or not this is afault, in the free world of the interchange of scientific ideas, is debatable. Myown feeling is that it leads more quickly to the ultimate solution of scientific problems than a cautious sitting on the fence. Indeed, I agree with Passmore(1965) that histories should even be polemical. Such histories will arousecontradiction and they will challenge the reader to come up with a refutation.By a dialectical process this will speed up a synthesis of perspective. Theunam-

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biguous adoption of a definite viewpoint should not be confused withsubjectivity.

The traditional admonition to historians has always been to be strictlyobjective. This ideal was well expressed by the great historian Leopold von

Ranke when he said the historian should "show how it really was." Historywas envisioned by him as the accurate reconstruction of a series of past events.Such objectivity is entirely appropriate when one attempts to answer who,what, when, and where, although it must be pointed out that even in presentingfacts the historian is subjective because he uses value judgments when sortingthe facts and is selective when deciding which ones to accept and how to relatethem to one another.

Subjectivity enters at every stage of history writing, especially whenone is seeking explanations and asks why, as is necessary in problematic

history. One cannot arrive at explanations without using one's own personal judgment, and this is inevitably subjective. A subjective treatment is usuallyfar more stimulating than a coldly objective one because it has a greaterheuristic value.

To what extent is subjectivity permissible and where does it become bias? Radl (1907-08), for instance, had such a strong antiDarwinian bias thathe was not even able to present the Darwinian theory adequately. This clearlywent too far. Subjectivity is apt to become bias whenever the evaluation of

scientists of former periods is involved. Here historians tend to go either to oneor to the other extreme. Either they adopt a strictly retrospective approach inwhich the past is evaluated entirely in the light of present knowledge andunderstanding, or else they suppress hindsight completely and describe pastevents strictly in terms of the thinking at that period. It seems to me that neitherapproach is entirely satisfactory.

A better procedure would be to combine the best aspects of bothapproaches. This would first attempt to reconstruct the intellectual milieu of

the period as faithfully as possible. But it would not be satisfactory to treat pastcontroversies strictly in terms of the information available at the time. Thiswould leave such controversies as unresolved and opaque as they were whenthey took place. Instead, modern knowledge should be used whenever thishelps in the understanding of past difficulties. Only such an approach willenable us to determine the reasons for the controversy and for the failure toresolve it. Was it a semantic difficulty (for example, the use of the same wordin different meanings), or a conceptual disagreement (such as essentialist vs. population think-

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ing), or an outright error (like the confusion of ultimate and proximatecauses)? A study of past controversies is particularly illuminating when thearguments and opposing viewpoints are analyzed in terms of our presentknowledge.

Semantic problems are particularly bothersome because they are sooften undiscovered. The Greeks, for instance, had a very limited technicalvocabulary and often used the same term for rather different things orconcepts. Both Plato and Aristotle used the term eidos (and Aristotle at least,used it in several senses!), but the major meaning of the term is totallydifferent in the two authors. Plato was an essentialist, but Aristotle wasessentialist only to a very limited extent (Balme, 1980). Aristotle used the termgenos occasionally as a collective noun (corresponding to the taxonomists'genus) but far more often in the sense of species. When Aristotle was

rediscovered in the late Middle Ages and translated into Latin and westernEuropean languages, his terms were translated in "equivalent" terms availablein medieval dictionaries. These misleading translations have had anunfortunate influence on our understanding of Aristotle's thought. Somemodern authors have had the courage to use modern terms to reveal Aristotle'sthought, terms he would have quite likely used if he were living today. I amthinking of Delbrück's use of "genetic program" to make clear Aristotle'sintention when using eldos in the description of individual development.

Likewise, one should use "teleonomy" (instead of "teleology") when Aristotlediscusses goal-directedness controlled by an eldos (program). This is notanachronistic but simply a way of making clear what an ancient authorthought, by using a terminology that is unambiguous for a modern reader.

It would, however, be quite inappropriate to use modern hindsight forvalue judgments. Lamarck, for instance, was not nearly as wrong as he seemsto those familiar with selectionism and Mendelian genetics, when judged interms of the facts known to him and of the ideas prevailing at his period. The

phrase "Whig interpretation of history" was introduced by the historianHerbert Butterfield (1931) to characterize the habit of some Englishconstitutional historians to see their subject as a progressive broadening ofhuman rights, in which good "forwardlooking" liberals were continuouslystruggling with the "backwardlooking" conservatives. Butterfield later (1957)applied the term whiggish to that kind of history of science in which everyscientist is judged by the extent of his contribution toward the establishment ofour current interpretation of science. Instead of evaluating a scientist in terms

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of the intellectual milieu in which he was active, he is evaluated strictly interms of current concepts. The complete context of problems and concepts inwhich the earlier scientists had worked is ignored in this approach. The historyof biology is rich in such biased whig interpretations.

Whenever there is a scientific controversy, the views of the losing sideare almost invariably later misrepresented by the victors. Examples are thetreatment of Buffon by the Linnaeans, of Lamarck by the Cuvierians, ofLinnaeus by the Darwinians, of the biometricians by the Mendelians, and soforth. The historian of biology must attempt to present a better balancedaccount. Many, now rejected theories, like the inheritance of acquiredcharacters espoused by Lamarck, seemed formerly so consistent with theknown facts that authors should not be criticized for having adopted such prevailing theories even if they have since been shown to be wrong. Almost

always those who held an erroneous theory had seemingly valid reasons fordoing so. They were trying to emphasize something that was neglected by theiropponents. The preformationists, for instance, attempted to stress somethingwhich was later resurrected as the genetic program. The biometricians upheldDarwin's views of gradual evolution against the saltationism of theMendelians. In both instances correct ideas were lumped together witherroneous ones and went down together with the errors. In my case I tend to pay special attention to underdogs (both persons and theories) because in the

past they have often been treated unfairly or at least inadequately.The path of science is never straight. There are always competing

theories and most of the attention of a period may be directed toward a sideissue which eventually turns out to be a dead end. These developments oftenilluminate the zeitgeist of a period more successfully than the straightforwardadvances of science. Regrettably, lack of space precludes an adequatetreatment of many of these developments. No history can afford to deal withevery lost cause and every deviation. There are, however, exceptions. Some of

the failures or errors of the past very suitably reveal aspects of contemporarythinking which we might otherwise miss. Macleay's and Swainson'squinarianism, for instance, which was totally eclipsed by the Origin ofSpecies, represented a sincere endeavor to reconcile the seeming chaoticdiversity of nature with the then prevailing conviction that there had to besome "higher" order in nature. It also reveals the still powerful hold of the oldmyth that all order in the world is ultimately numerical. As ill-

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conceived and ephemeral as the theory of quinarianism was, it neverthelesscontributes to our understanding of the thinking of its period. The same can besaid of almost any theory or school of the past that is no longer consideredvalid. The interests of a historian necessarily influence his decision as to whichsubjects to treat in detail and which others in a more cursory fashion. I tend toagree with Schuster, who said in The Progress of Physics (1911), "I prefer to be frankly subjective, and warn you beforehand that my account will befragmentary, and to a great extent reminiscent of those aspects which havecome under my own personal view."

Historians versus Scientists

Two groups of scholars with entirely different viewpoints and backgrounds-historians and scientists ― have claimed the history of science

as their own. Their respective contributions are somewhat different, dictated by differences in their interests and competence. A scientist tends to select foranalysis and discussion rather different problems from a historian orsociologist. For instance, in recent accounts of evolution by variousevolutionists, H. Spencer has hardly received any attention. There are goodreasons for this neglect. Not only was Spencer vague and confused, but theideas he championed were those of others and already obsolete when taken up by Spencer. That Spencer's borrowed ideas were quite popular and influential,

as far as the general public was concerned, is without question true, but it is notthe task of the scientist-historian to trespass in the domain of the sociologist.Biologists usually lack the competence to deal with social history. On the otherhand, it would be just as ridiculous to demand that a social historian present acompetent analysis of the scientific issues. The history of science derivesinspiration, information, and methodological assistance both from science andfrom history and, in turn, contributes by its findings to both fields.

There are valid reasons for the interest of both historians and scientistsin the history of science. The Greeks had no science, as we now define it, andwhatever science they had was practiced by philosophers and physicians.After the Middle Ages there was a continuing trend of emancipation of sciencefrom philosophy and from the general zeitgeist. In the Renaissance period andduring the eighteenth century scientific beliefs were strongly influenced by thescientists' attitude toward religion and philosophy. A Cartesian, an orthodoxChristian, or a Deist would inevitably have different ideas on cosmology,generation, and all aspects of the

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interpretation of life, matter, and origins. Nothing signaled the emancipationof science from religion and philosophy more definitely than the Darwinianrevolution. Since that time it has become quite impossible to say by looking atan author's scientific publications whether he was a devout Christian or anatheist. Except for a few fundamentalists, this is true even for the writings of biologists on the subject of evolution.

This trend toward the emancipation of science had a considerable effecton the writing of the history of science. The farther back we go in time, the lessimportant becomes the store of scientific knowledge of the period and themore important the general intellectual atmosphere. As far as biology isconcerned, it is not until after about 1740 that the scientific problems begin toseparate themselves from the general intellectual controversies of the period.There is no question that historians are particularly well qualified to deal with

the earlier time span in the history of biology. However, the nineteenth andtwentieth centuries' history of special biological disciplines was entirelydominated by scientists, until its rather recent professionalisation. This is wellillustrated by such recent histories of special areas in biology, as those ofDunn, Stubbe, and Sturtevant in genetics, of Fruton, Edsall, and Leicester in biochemistry, of Needham and Oppenheimer in embryology, of Baker andHughes in cytology, of Stresemann in ornithology, to mention only a fewnames in the extensive literature. They demonstrate the qualification of

scientists for historical research.The Bias of the Physical Scientists

Most general histories of "science" have been written by historians of physics who have never quite gotten over the parochial attitude that anythingthat is not applicable to physics is not science. Physical scientists tend to rate biologists on a scale of values depending on the extent to which each biologisthas used "laws," measurements, experiments, and other aspects of scientificresearch that are rated highly in the physical sciences. As a result, the judgments on fields of biology made by certain historians of the physicalsciences that one may find in that literature are so ludicrous that one can onlysmile. For example, knowing that Darwin developed his theory of evolutionlargely on the basis of his observations as a naturalist, one can only marvel atthis statement, made by a well-known historian of Newton: "The naturalist isindeed a trained observer, but his observations differ from those

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of a gamekeeper only in degree, not in kind; his sole esoteric qualification isfamiliarity with systematic nomenclature." This kind of biased physicalistthinking is entirely out of place in the study of evolutionary biology, as weshall see in Chapter 2. Theory formation and its history in evolutionary andsystematic biology require a radically different approach, an approach whichis in some ways more similar to that adopted by a historian of archeology or byan interpreter of modern world history.

Other Biases

Not just the physicist but every specialist, quite naturally, considers his particular field of research to be the most interesting and its methods to be themost productive. As a result, often an invidious kind of chauvinism existsamong fields, and even within a field such as biology. It is chauvinism, for

instance, when Hartmann (1947) allotted 98 percent of his large General Biology to physiological biology and only 2 percent to evolutionary biology. Itis chauvinism when certain historians ascribe the occurrence of theevolutionary synthesis entirely to the findings of genetics, completely ignoringthe contribution made by systematics, paleontology, and other branches ofevolutionary biology (Mayr and Provine 1980).

There is sometimes also a national chauvinism within a field whichtends to exaggerate or even to misrepresent the importance of the scientists

from the writer's own country and to belittle or ignore scientists of othernations. This is not necessarily due to misplaced patriotism but is often theresult of an inability to read the languages in which important contributions byscientists of other countries have been published. In my own work I am keenlyaware of the probability of bias introduced by my inability to read Slaviclanguages and Japanese.

Pitfalls and Difficulties

The greatest difficulty in the endeavor to identify the vast number of problems of biology and to reconstruct the development of its conceptualframework is the vast amount of material to be studied. This consists, in principle, of the entire store of knowledge of biology, including all books and periodical articles published by biologists, their letters and biographies,information on the institutions with which they were associated, contemporarysocial history, and much else. Not even the most conscientious

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historian would be able to cover even one tenth of one percent of all thismaterial. The situation is aggravated by the exponential acceleration in the rateof current scientific output. In an amazingly short span of years more papers(and pages!) are now published than in the whole preceding history of science.Even specialists complain that they can no longer keep up with the avalancheof research output in their own field. Curiously, exactly the same is true forhistory writing. In the United States there are now perhaps five times as manyhistorians of biology as there were only twenty-five years ago.

Even though I have valiantly attempted to read the most important publications, I know that every specialist will discover numerous omissions inmy treatment and presumably not infrequent errors. The first draft of most ofthe manuscript was written from 1970 to 1976 and the more recently publishedliterature is not always as adequately incorporated as would have been

desirable. My task would have been altogether impossible if it had not been forthe richness and excellence of the modern secondary literature. The olderliterature was often rather superficial, and author after author would copy thesame myths or errors, as one discovered when one consulted the original publications. Obviously, in a volume such as this one, which may containmore than 20,000 individual items of information, it is impossible to verifyeach item in the original source. Since my work is not a lexicographic history,an occasional factual error is not fatal. My major objective has been to

synthesize an enormous literature with a consistent emphasis on interpretationand the analysis of causation.

Timeliness

A criticism often raised against historians of science, and not without justification, is that they are preoccupied too exclusively with the "prehistory"of science, that is, with periods the events of which are largely irrelevant formodern science. To avoid this complaint I have tried to bring the story as closeto the present as is possible for a nonspecialist. In some cases, for instance thediscovery in the last five to ten years in molecular biology of numerousfamilies of DNA, the conceptual consequences (for instance on evolution) arestill too uncertain to be dealt with.

I disagree with the statement of a recent historian that "the object of thehistory of science is investigation and disputes that have been concluded ratherthan issues that are presently alive." This is quite in error. Most scientificcontroversies extend over far

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longer periods of time than is generally conceived. Even today's controversieshave a root that usually goes far back in time. It is precisely the historical studyof such controversies that often contributes materially to a conceptualclarification and thus makes the ultimate solution possible. Analogous to thefield of world history, where "current history" is recognized as a legitimatefield, there is "current history" in the history of science. Nothing would bemore misleading than to assume that the history of science deals only withdead issues. On the contrary, one might even go so far as to consider as prehistory the accounts of long-dead issues of earlier centuries and millennia.

Simplification

A historian who covers such a vast area as is dealt with in this volume isforced to present a highly streamlined account. The reader is warned that the

seeming simplicity of many of the developments is quite deceiving. Detailedaccounts that concentrate on special developments or short periods must beconsulted if one is to appreciate the full flavor of the many cross currents, falsestarts, and unsuccessful hypotheses that prevailed at any given period.Developments virtually never were as straightforward and logical as theyappear to be in a simplified retrospective account. It is particularly difficult toemphasize adequately the often quite paralyzing power of entrenchedconceptualizations when confronted by new discoveries or new concepts.

Inaccuracy is also introduced by labeling certain authors as vitalists, preformationists, teleologists, saltationists, or neo-Darwinians, as if theselabels would refer to homogeneous types. Actually, these categories consist ofindividuals no two of whom had exactly the same views. This is particularlytrue for the epithets "Lamarckians" and "neo-Lamarckians," some of whomhad nothing in common with each other except a belief in an inheritance ofacquired characters.

Silent Assumptions

A further difficulty for the historian is posed by most scientists'unawareness of their own framework of ideas. They rarely articulate ― if theythink about it at all ― what truths or concepts they accept without question andwhat others they totally reject. in many cases the historian can piece thistogether only by reconstructing the total intellectual milieu of the period. Andyet an understanding of these silent assumptions may be necessary in

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order to answer previously puzzling questions. In science one always dealswith priorities and value systems; they determine the direction of new researchafter a previous piece of research has been completed; they determine whichtheories the investigator is most anxious either to confirm or to refute; theyalso determine whether or not he considers an area of research exhausted. Andyet a study of the factors that determine such priorities or value systems has been greatly neglected until now. The historian must attempt to find out whatwent on in the mind of a worker when he gave a new interpretation to a longfamiliar set of facts. It is perhaps legitimate to say that the truly crucial eventsin the history of science always take place in the mind of a scientist. One must,so to speak, attempt to think as the scientist thought when he performed thework one is trying to analyze.

Most scientists tend to concentrate in their publications on new facts or

rather on new discoveries, and in particular on anything that is spectacular. Atthe same time they usually fail to record important ongoing changes ofconcepts or emphasis. They may even fail to recognize such changes or mayconsider them as negligible even when they are aware of them. When themodern historian attempts to reconstruct such changes in past centuries, hecannot help but project into history the interests and scale of values of the present. This danger of interpretation can be minimized only if the historian isfully aware of what he is doing.

Why Study the History of Biology?

My own interest in the history of science was aroused by reading A. O.Lovejoy's The Great Chain of Being, where the attempt is made ― and it waseminently successful ― to trace the life history, so to speak, of a single idea(or a cohesive complex of ideas) from the ancients to the end of the eighteenthcentury. I have learned more from this one volume than from almost anythingelse I have read. Others who have attempted a similar approach are ErnstCassirer and Alexander Koyré. They have provided entirely new standards forscientific historiography.

In the case of the history of science, the focal points are problems ratherthan ideas, but the approach of the historian of science is not much differentfrom that of a historian of ideas such as Lovejoy. Like Lovejoy, he attempts totrace the problem back to its beginning and to follow up its fate and itsramifications from such a beginning either to its solution or to the present time.

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It is the principal objective of this volume to discover for each branchof biology and for each period what the open problems were and what proposals were made to solve them; the nature of the dominant concepts, theirchanges, and the causes for their modification and for the development of newconcepts; and finally, what effect prevailing or newly arising concepts had indelaying or accelerating the solution of the open problems of the period. At its best this approach would portray the complete life history of each problem of biology.

Preoccupation with this sort of conceptual history of science issometimes belittled as a hobby of retired scientists. Such an attitude ignoresthe manifold contributions which this branch of scholarship makes. Thehistory of science, as has been pointed out frequently, is particularly suitableas a first introduction to science. It helps to bridge the gap between "general

beliefs" and the actual findings of science, since it shows in what manner andfor what reasons science has advanced beyond the beliefs of folklore. Toillustrate this for a single branch of biology, in the history of genetics it can beshown by what discoveries and arguments rather widely held erroneous beliefswere refuted, as for instance that there is an inheritance of acquired characters;that the genetic materials of the parents "blend"; that the "blood" of a female istainted so that she can never again produce "pure" offspring once she has beeninseminated, even if only a single time; that a single egg is simultaneously

fertilized by the sperm of several males; or that accidents of a pregnant mothercan lead to the production of heritable characters. Similar erroneous beliefs,derived from folklore, myths, religious documents, or from early philosophies,had originally been held in many fields of biology. The historicaldemonstration of the gradual replacement of these prescientific or earlyscientific beliefs by better based scientific theories and concepts greatly assistsin explaining the current framework of biological theories.

The layperson often excuses his ignorance of science with the comment

that he finds science too technical or too mathematical. Let me assure the prospective reader of this volume that he will hardly find any mathematics inits pages and that it is not technical to the extent that a layperson would havedifficulty with the exposition. It is a major advantage of the history of ideas in biology that one can study it without a background knowledge of the name of asingle species of animal or plant or of the major taxonomic groups and theirclassification. However, a student of the

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history of ideas must acquire some knowledge of the dominant concepts in biology, like inheritance, program, population, variation, emergence, ororganismic. It is the objective of Chapter 2 to provide an introduction into theworld of major biological concepts. Many of these concepts (and the terms thatgo with them) have now also been incorporated into various branches of thehumanities, and it has simply become a matter of education to be acquaintedwith them. All of these concepts are indispensable for an understanding of manand the world in which he lives. Any endeavor to elucidate the origin andnature of man must be based on a thorough understanding of the concepts andtheories of biology. Finally, it is helpful to become familiar with a very smallrepertory of technical terms like gamete, zygote, species, gene, chromosome,and so on, terms that are defined in the Glossary. Yet, the total vocabulary ofsuch technical terms is far smaller than what a student in any field of the

humanities has to learn, whether it be music, literature, or current history.It is not only the layperson whose horizon will be greatly extended by

the study of the history of ideas in biology. Advances in many areas of biologyare so precipitous at the present time that specialists can no longer keep upwith developments in areas of biology outside their own. The broad survey of biology and its dominant concepts that is presented in this volume will help infilling some of the gaps. My survey is also directed toward those who haveentered biology in recent years from the outside, that is, from chemistry,

physics, mathematics, or other adjacent fields. The technical sophistication ofthese "neo-biologists" is, unfortunately, rarely matched by an equivalentconceptual sophistication. Indeed, those who know organisms in nature andunderstand the ways of evolution are often appalled by the naiveté of some ofthe generalizations made in some papers in molecular biology. Admittedly,there is no quick and easy way to compensate for this deficiency. Like Conant,I feel that the study of the history of a field is the best way of acquiring anunderstanding of its concepts. Only by going over the hard way by which these

concepts were worked out―

by learning all the earlier wrong assumptionsthat had to be refuted one by one, in other words by learning all past mistakes― can one hope to acquire a really thorough and sound understanding. Inscience one learns not only by one's own mistakes but by the history of themistakes of others.

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2 The place of biology in the sciences and its conceptual structure

IT IS QUITE impossible to try to understand the development of any particular concept or problem in the history of biology unless one has firstanswered for oneself these questions: What is science? What is the place of

biology among the sciences? And what is the conceptual structure of biology?Entirely misleading answers have been given to all three of these questions, particularly by philosophers and other nonbiologists, and this has greatlyimpeded an understanding of the growth of biological thought. To try toanswer these basic questions correctly, then, is the first task of my analysis. Itwill provide a secure basis for the study of the history of specific concepts.

THE NATURE OF SCIENCE

From the earliest times on man has asked questions about the origin andthe meaning of the world and frequently about its purpose. His tentativeanswers can be found in the myths characteristic of every culture, even themost primitive ones. He has advanced beyond these simple beginnings in tworather different directions. In one his ideas became formalized in religions,which proclaimed a set of dogmas, usually based on revelation. The Westernworld, for instance, at the end of the Middle Ages was completely dominated by an implicit trust in the teachings of the Bible, and beyond that, by auniversal belief in the supernatural.

Philosophy, and later science, is the alternative way of dealing with themysteries of the world, although science was not strictly separated fromreligion in its early history. Science confronts these mysteries with questions,with doubts, with curiosity, and with explanatory endeavors, thus with a ratherdifferent attitude from religion. The pre-Socratic (Ionian) philosophersinitiated this different approach by searching for "natural" explanations, interms of observable forces of nature, like fire, water, and air (see Chap-

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ter 3). This endeavor to understand the causation of natural phenomena wasthe beginning of science. For many centuries after the fall of Rome thistradition was virtually forgotten, but it was revived again in the late MiddleAges and during the scientific revolution. The belief grew that the divine truthwas revealed to us not only in Scripture but also in God's creation.

Galileo's statement of this opinion is well known: "I think that in thediscussion of natural problems we ought not to begin at the authority of placesof Scripture, but at sensible experiments and necessary demonstrations. For,from the Divine Word the sacred Scripture and Nature did both alike proceed."He continued that "God equally admirably reveals Himself to us in Nature'sactions as in the Scriptures' sacred dictions." He thought that a god whogoverns the world with the help of eternal laws inspires trust and faith at leastas much as one who forever intervenes in the course of events. It was this

thought which gave rise to the birth of science as we now understand it.Science for Galileo was not an alternative to religion but an inseparable part ofit. Likewise, many great philosophers from the seventeenth to the nineteenthcenturies ― for instance, Kant ― included God in their explanatory schemes.So-called natural theology was, in spite of its name, as much science as it wastheology. The conflict between science and theology developed only laterwhen science explained more and more processes and phenomena of nature by"natural laws" which previously had been considered inexplicable except by

the intervention of the Creator or by special laws or

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