The Logic of Life: A History of Heredity

By François Jacob and Matthew Cobb

“The most remarkable history of biology that has ever been written.”—Michel Foucault

Nobel Prize–winning scientist François Jacob’s The Logic of Life is a landmark book in the history of biology and science. Focusing on heredity, which Jacob considers the fundamental feature of living things, he shows how, since the sixteenth century, the scientific understanding of inherited traits has moved not in a linear, progressive way, from error to truth, but instead through a series of frameworks. He reveals how these successive interpretive approaches—focusing on visible structures, internal structures (especially cells), evolution, genes, and DNA and other molecules—each have their own power but also limitations. Fundamentally challenging how the history of biology is told, much as Thomas Kuhn’s Structure of Scientific Revolutions did for the history of science as a whole, The Logic of Life has greatly influenced the way scientists and historians view the past, present, and future of biology.

• Language: English
• Publisher: Princeton University Press
• Release date: Aug 2, 2022
• ISBN: 9780691238999

Book preview

Cover: The Logic of Life by François Jacob

The Logic of Life

Other books by François Jacob

THE POSSIBLE AND THE ACTUAL

François Jacob

THE LOGIC OF LIFE

A History of Heredity

Translated by Betty E. Spillmann

With a new foreword by Matthew Cobb

PRINCETON UNIVERSITY PRESS

PRINCETON, NEW JERSEY

Published by Princeton University Press, 41 William Street,

Princeton, New Jersey 08540

99 Banbury Road, Oxford OX2 6JX

English translation copyright © 1973 by Betty E. Spillmann

Foreword to the Princeton Science Library edition copyright ©

2022 by Princeton University Press

All rights reserved

Originally published in France as La logique du vivant: une histoire de l’hérédité by Editions Gallimard, Paris; copyright © 1970 by Editions Gallimard. English translation first published in Great Britain as The Logic of Living Systems: A History of Heredity, by Allen Lane, a division of Penguin Books Limited, London. First published in America by Pantheon Books, a Division of Random House, Inc., New York, and reprinted here in the Princeton Science Library series by permission of Random House, Inc.

First Princeton paperback printing, 1993

New Princeton Science Library edition, with a new foreword by Matthew Cobb, 2022

New paperback ISBN 9780691182841

ISBN (e-book) 9780691238999

Version 1.0

Library of Congress Control Number: 2021948908

www.press.princeton.edu

Do you see this egg? With it you

can overthrow all the schools of theology,

all the churches of the earth.

DIDEROT

Conversation with d’Alembert

Contents

Foreword by Matthew Cobb ix

Preface xxi

Introduction The Programme1

1 The Visible Structure19

Generation20

Deciphering Nature28

Mechanism32

Species44

Preformation52

Heredity67

2 Organization74

Memory and Heredity75

The Hidden Architecture82

Life88

The Chemistry of Life92

The Plan of Organization100

The Cell111

3 Time130

Cataclysms131

Transformations142

Fossils152

Evolution160

4 The Gene178

Experimentation180

Statistical Analysis192

The Birth of Genetics201

The Dance of the Chromosomes209

Enzymes226

5 The Molecule247

Macromolecules249

Micro-organisms260

The Message267

Regulation279

Copy and Error286

Conclusion The Integron299

Notes325

Index339

Foreword

In 1970, François Jacob (1920–2013) published La logique du vivant, a book that soon had a significant influence on the way scientists, historians, and the general public viewed the past, present, and future of biology. Five years earlier, Jacob had shared the Nobel Prize in Physiology or Medicine with his Institut Pasteur colleagues Jacques Monod and André Lwoff. This award, for their work on the genetic control of the synthesis of enzymes and viruses, was one of a series of Nobel Prizes to recognise the huge breakthroughs in molecular biology that occurred in the 1950s and 1960s, and it came at a paradoxical moment. At the same time that molecular biology was internationally recognised as a major new discipline and thousands of researchers around the world began to work in the area, most of the founders of the field were leaving, turning their attention to the nervous system or cancer. Jacob, who had been one of the pioneers, shared this uncertainty about the future. Having reached the heights of scientific achievement, he began to wonder what it was all about, and more specifically, as he recalled in 2004, ‘why we got to where we were.’ (Lwoff and Monod appear to have had a similar experience; both men also published popular science books at around the same time—Lwoff’s L’ordre biologique appeared in 1969 and Monod’s Chance and Necessity in 1970.)

As Jacob mused about where to turn his scientific attention—shortly after this book appeared, he began to study embryonic development in the mouse—he looked at various histories of biology to answer his deep questions about the shape of science. He was disappointed with what he found—as he said in 1995, ‘I leafed through two or three books on the history of biology, but they did not seem to me to have the right way of presenting things.’ For Jacob, the history books, like scientific articles, presented a version of scientific discovery that was at odds his experience. He told the New York Times in 1974: ‘I was not very happy about the way they tell the history of biology. In each paper, a scientist writes what his predecessors learned, and so forth, and winds up with linear history, from error to truth. It’s not like that.’

The history of biology has moved on a bit since then, and whatever the validity of this view of the state of the field in the late 1960s, any scientist embarking on a similar task today would be well advised not only to follow Jacob’s example and to read the original sources, but also to start by reading some of the many studies of the history of biology, such as this book. As Jacob later admitted, after La logique du vivant was published he discovered that some aspects of his approach had already been employed by the philosopher Karl Popper, and by scientists such as Ernst Mayr and Michael Ghiselin.

Instead of seeing science as a story of endless incremental progress, Jacob argued that each period of science was marked by a particular approach or overall framework—a ‘range of possibilities,’ as he put it. These frameworks enabled thinkers to explore the natural world but also limited the questions they could ask, the theories they could develop, and even the nature of the objects that could be studied. As new approaches, techniques, and frameworks appeared, new questions could be asked and old certainties could be revisited.

Although Jacob did not acknowledge it, this view echoed two approaches to history that were becoming enormously influential in academic circles. In 1962, the philosopher of science Thomas Kuhn published The Structure of Scientific Revolutions, in which he presented the history of science as a succession of what he called paradigms. These were discontinuous, mutually incompatible interpretative frameworks; when one paradigm replaced another, as for example when seventeenth-century Newtonian mechanics replaced the Aristotelian vision, there would be an abrupt change in worldview. A more direct influence on Jacob was the work of the French philosopher and historian Michel Foucault, who in 1966 published Les mots et les choses (translated as The Order of Things in 1970) in the same series as Jacob’s book. In 1967, Jacob told his publisher, Pierre Nora, he had devoured Foucault’s book over the summer. In Les mots et les choses, which focused on the history of the human sciences, Foucault used the concept of épistémè (from the Greek for ‘knowledge’), an overall interpretative and analytical framework that shaped cultural understanding of all kinds of objects. Despite their apparent similarities and their near-simultaneous appearance, each of these three interpretative approaches developed by Kuhn, Foucault, and Jacob had very different origins and implications. Each has its own specificity and its own cultural and sociological meaning.

For Jacob, the key issue was to understand how different kinds of objects became available for scientific analysis at different points in history, leading to the discovery of new concepts and understanding. This framework can be seen in the structure of the book—each chapter corresponds to a level of understanding or approach from a particular historical period. The chapter titled ‘The Visible Structure’ relates to external analyses of organisms, which dominated until the second half of the eighteenth century; ‘Organization’ focuses on the understanding of the role of internal structures, in particular cells; ‘Time’ explores how the theory of evolution by natural selection situated life in the context of the deep history of Earth; ‘The Gene’ shows how statistical analysis was necessary to detect the phenomena of heredity, while ‘The Molecule’ describes the new world we entered with Oswald Avery’s 1944 demonstration that genes are made of DNA, and the discovery by James Watson and Francis Crick, using data and ideas from Rosalind Franklin and Maurice Wilkins (neither of whom are mentioned), that DNA has a double helix structure. Each of these approaches or levels of analysis—at several points Jacob calls them ‘Russian dolls,’ evoking their nested nature—comes with its own power, insights, and limitations.

Jacob emphasised in the subtitle of his book that this is not a history of biology but rather a history of heredity. Areas of biology such as anatomy or physiology have their role to play, but only at the relevant point in the chronology (the first two chapters, respectively, in these cases), and ultimately they are only seen as significant in terms of how they shed light on heredity, which Jacob considered to be the fundamental feature of living things.

This last point highlights a difference between the original French title and the translated title by which the book is now known in the English-speaking world. The French original La logique du vivant (The logic of living things), has different implications from the current title, The Logic of Life (the original 1973 UK title was the more faithful The Logic of Living Systems; the 1973 US title was the truncated version we know today).

‘Life’ as an abstract phenomenon is something that is not referred to much in the book, for the simple reason that since the early years of the twentieth century and the waning of vitalism, biologists have not been particularly interested in the topic. We are curious about how life appeared, about whether there may be life elsewhere in the universe, and we can get into pub arguments about whether, say, viruses are alive (they are not). But musing about the logic of life, rather than the logic of living things, is not something Jacob devotes much time to in his book, because it is not something that scientists do very much. This was noticed in 1975 by the French philosopher Jacques Derrida, who pointed out in his unpublished seminar ‘La vie la mort’ that Jacob could have called the book La logique de la vie, but he chose not to.

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There are two pivotal moments in Jacob’s history of heredity. The first hinges on a change in a single word—the eighteenth-century appearance of the term ‘reproduction’ to describe the process by which life appears. By the middle of the nineteenth century, this had entirely replaced the word that had dominated since antiquity: ‘generation.’ ‘Generation’ refers to the origin and growth of organisms, while ‘reproduction’ was initially coined to describe the literal reproduction of parthenogenetic organisms such as aphids, in which the females reproduce themselves without the involvement of any males. In the hands of the French naturalist Georges-Louis Leclerc, Comte de Buffon, ‘reproduction’ soon began to change its meaning, referring to the propagation of individuals and of the species. Although ‘sexual reproduction’ is now the accepted term to describe, say, the production of new humans, this process does not actually involve ‘reproduction.’ You are not a copy of either of your parents but a unique mixture of both of them. We do not notice it, but ‘reproduction’ is fundamentally a misnomer, a relic of a previous way of understanding one particular form of life. Over the past half century, scholars from different disciplines have explored the reasons for the shift from ‘generation’ to ‘reproduction’ and its cultural ramifications. This involved much more than mere biology—the growth of capitalism, increased mechanisation, and the changing role of women in this period have all been identified as contributory factors that shed light on the change in terminology.

Before Jacob began his historical exploration, this eighteenth-century change in biological terminology had been studied in great detail by the brilliant young French historian Jacques Roger in his book Les sciences de la vie dans la pensée française au XVIIIe siècle (it is not known if Jacob read this; it is hard to imagine that he did not). As Roger explained, following developments in the seventeenth century, in particular the extraordinarily delicate and precise dissections and experimental observations of Jan Swammerdam, most thinkers were ‘ovists.’ They believed that the new organism was somehow wrapped up in the egg (this idea was called ‘preformation’). The role of the male was thought to be that of somehow awakening the form that was in the egg.

Ovism represented a profound change from the dominant view, which went back to the ancient Greeks and beyond, namely, that the female provided mere nourishment or matter while the male shaped the offspring through his semen (the word means ‘seed’ in Greek—embarrassed parents may still explain to children that ‘Daddy put a seed in Mummy’s tummy’). Even though sperm were observed by Antonie van Leeuwenhoek in 1677, this did not shake the then-dominant ovist view: most thinkers considered them to be some kind animal. This can be seen in the word we still use for them—‘spermatozoa,’ which means ‘the animal that lives in semen.’ This is yet another now-unnoticed misnomer; the man who coined the term in 1827, Karl Ernst von Baer, classified them as a particular kind of parasitic worm.

This highlights what looks like a massive paradox that, in retrospect, appears to have dominated biological thinking for over a century and a half. Von Baer was also the first person to observe the human egg, and yet he did not realise that the two structures he had described, egg and sperm, were equivalents—he remained a firm believer in ovism. The reason for this common blind spot among all thinkers from the seventeenth century onwards fits into Jacob’s conception of the history of science. Eggs were single, immobile things, either large (birds, reptiles) or incredibly tiny and hard to observe even with a microscope (mammals). Spermatozoa, on the other hand, were uniformly minuscule, present in mind-boggling numbers, and were furiously active. There was no reason to imagine that these two things were equivalents—the female and male contributions that fused together to form new life. That only became evident with the developments in microscopy that enabled the rise of cell theory at the end of the 1830s, when both egg and sperm could be understood to be sex cells, and, decades later, with the first microscopical observations of fertilization in sea urchins.

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At the same time as these changes were happening, another profound conceptual shift was occurring, one that Jacob surprisingly barely refers to. The very topic of his book—heredity—was coming into being at this time. As Carlos López-Beltrán has shown, up until the early years of the nineteenth century, ‘heredity’ did not exist as a noun, outside of legal documents relating to the capacity to inherit things from a deceased relative. The French term hérédité began to take on a biological meaning only in the 1830s, referring to a force that expressed itself across generations; the English equivalent, ‘heredity,’ was first used by Herbert Spencer in 1863 (the term appears in Charles Darwin’s notes at the same period). Although physicians recognised that there were inherited diseases, prior to the early decades of the nineteenth century there was no understanding—anywhere in the world, not just among the scholars and thinkers of Europe—that heredity as an overall phenomenon actually existed.

Many readers will find this claim so counterintuitive that they will refuse to accept it, insisting that people have always known that there was such a thing. It is true that folk knowledge had suggested for millennia that ‘like breeds like’ (Jacob claims in his opening sentence that this is ‘immediately evident’), but folk knowledge also accepted that this was not always true, and despite the best endeavours of many thinkers, it proved impossible to generalise this impression into something like a law. To give two examples of the kinds of problems that were faced by those who sought to understand what was happening: farmers regularly made crosses between animal or plant breeds where the resultant offspring did not resemble either parent, and there were even outlandish breaches of the concept, such as the widespread early-eighteenth-century belief that Mary Toft of Godalming in Sussex gave birth to rabbits (there were many similar tales—Toft was not alone in her uncanny ability). Like bred like, except when it did not.

Casual observation could not reveal if there was some underlying coherence to the links that could sometimes be seen between parents and offspring. Experimentation was necessary. In the seventeenth century, Swammerdam and Francesco Redi demonstrated that there was a lawfulness about generation, and that, as Swammerdam put it in 1669, all life comes ‘from an egg laid by a female of the same species.’ This statement, which looks banal to us, was revolutionary at a time when the learned gentlemen of the Royal Society of London were attempting to generate vipers from dust. But even Swammerdam could not satisfactorily explain what the role of male and female were, nor reveal the links between parents and offspring.

This widespread uncertainty about the systematic reality of hereditary phenomena relates to a second key point made by Jacob—the importance of statistical, populational analysis, which he claims was developed at the end of the nineteenth century by Ludwig Boltzmann and Josiah Willard Gibbs in physics and, earlier, by Darwin in biology. This argument, which repeats the claims in a 1944 article in Nature by the physicist Erwin Schrödinger, looks rather schematic today. There was indeed a vital link between population-level statistical exploration of data and the development of the concept of heredity, but it was not that statistics gave a quantitative form to heredity, but rather that it revealed the existence of heredity itself. All this took place well over a century before Boltzmann and Gibbs.

In the eighteenth century, three very different approaches converged on the use of population analysis and led to the revelation of the existence of heredity. Two of these approaches were French and were related to patterns of inheritance of certain conditions in humans. The first was developed in the middle of the century by Pierre Louis Moreau de Maupertuis and René-Antoine Ferchault de Réaumur, who each explored polydactyly—the presence of more than five digits on a hand—in families. Multigenerational genealogies revealed that preformation could not explain the observed pattern (parents and offspring were not necessarily identical), nor was polydactyly rare in these families, so these were not ‘monsters.’ Maupertuis even carried out a primitive probability calculation to determine if the observed pattern could have occurred by chance (it could not).

The implication of Réaumur and Maupertuis’s observations was that there was an underlying, unknown force shaping the appearance of polydactyly down the generations, but there was no explanation of why polydactyly sometimes appeared and sometimes did not—like did not necessarily breed like in these genealogies. At around the same time, in a second and parallel approach, French physicians became interested in how hereditary diseases might be passed from one generation to another, using family trees to interpret the patterns of inheritance of these conditions. These discussions continued until the early years of the nineteenth century, by which time scores of medical theses had been written on the topic. The role of heredity in producing some conditions began to become real in physicians’ minds, but the exact logic of the patterns they detected, and their physical basis, remained obscure.

Meanwhile, on the other side of the Channel, a third route to heredity was taking form, through the work of sheep breeders. The most significant of these figures was a Leicestershire farmer, Robert Bakewell, who began to selectively breed sheep that would grow more quickly. The key feature of Bakewell’s work was that he kept detailed records of the large numbers of matings that he planned and the characters of the parents and their offspring. What had previously been an intuitive, small-scale process of selective breeding carried out for thousands of years, now became massive, on an industrial scale to feed the growing populations of Britain’s new industrial cities. Bakewell’s vast and detailed records revealed that something related to the characters that he was interested in was being passed down the generations. The exact pattern and mechanism were unclear, but Bakewell cared little—he was a practical man, and the main thing that concerned him was that his selective breeding worked.

The success of Bakewell’s process not only made him very rich—his sheep grew to selling weight in half the time of traditional breeds—it also attracted the attention of both the Royal Society and other agriculturalists. News of his work soon reached central Europe, where the leaders of the wool industry around Brnö in Moravia decided they wanted to emulate Bakewell’s breeding process, but with wool as the focus, rather than mutton. In the early decades of the nineteenth century, businessmen and thinkers around Brnö began to search for what they called ‘genetic laws’ that might explain patterns of inheritance and enable them to produce better crops and stronger livestock. But they struggled because it was impossible to know in advance what the offspring of two different strains of a particular organism might look like. In 1837, this problem of predicting the nature of hybrids led Abbot Napp, the head of the Brnö monastery, which owned large stretches of farmland and had a major interest in improving crops and livestock, to ask the fundamental question: ‘What is inherited, and how?’ To answer that conundrum, six years later Napp welcomed a young monk, Gregor Mendel, and set him to work on finding an answer, using the large data sets and populational approaches that had been pioneered in the eighteenth century. Mendel was able to describe the lawfulness of heredity, and when his work was rediscovered at the beginning of the twentieth century, genetics was born.

Although Schrödinger and Jacob were incorrect in identifying when this insight came into science, they were absolutely right to point to the importance of statistical analysis in revealing hereditary phenomena, which are not absolute but conditional. These phenomena only reveal themselves when you have large data sets that span several generations. Simply observing intriguing (dis)similarities between parents and offspring is not sufficient—humans had been doing that since the dawn of time and had not been able to come up with a coherent explanation.

This complex nature of the origin of heredity as a concept highlights another surprising aspect of Jacob’s book—it contains few references to developments in the outside world. To some extent this is therefore an internalist account of the history of science—science is something that is done in the philosopher’s drawing room or cabinet of curiosities, and later in the laboratory. In that respect, despite Jacob’s rejection of science as a continual progression and his relative lack of interest in the role of individual scientists, this is still very much a scientist’s view of his subject. As the work of Nick Hopwood, Staffan Müller-Wille, Hans-Jörg Rheinberger, and others has shown over recent decades, anyone seeking to emulate Jacob’s work today would look at a broader cultural history of heredity and its multiple meanings and implications, not just focus on the work of those we now call scientists.

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Jacob’s book has been extremely influential. Cited well over a thousand times, it has become an object of study itself, as scholars have dissected its influences and how it has affected scientists, historians, and the general public. Inevitably, it is a product of its time. Jacob’s occasional Gallic 1960s attitudes (for example, referring to the concept of goal-directed behaviour, or teleology, he claimed that in the past the biologist ‘treated teleology as he would a woman he could not do without, but did not care to be seen with in public’) will grate with some readers, but such lapses are few. When published, it was widely reviewed in the academic press—Science even reviewed it twice, once for the French edition and then again for the translation (both reviews were very positive). Probably the most widely quoted review was from Foucault, in the pages of Le Monde. Foucault described it as ‘a real, great book of history’; indeed, he argued it was ‘the most remarkable history of biology that has ever been written.’ This is perhaps not surprising given the obvious connections between the two men’s ideas—the French philosopher of science Georges Canguilhem pointed out the similarities in language and tone between Jacob’s and Foucault’s writings.

Probably the most significant similarities, however, are to be found in the work of the American evolutionary biologist, Ernst Mayr. One of the most arresting statements in Jacob’s book comes in the opening chapter, where he explains the significance of the metaphor of a computer programme for understanding gene function. Jacob brought the new way of looking at heredity, based on metaphors from the computer age, to the attention of the general public: ‘In the genetic programme, therefore, is written the result of all past reproductions, the collection of successes, since all traces of failures have disappeared. The genetic message, the programme of the present-day organism, therefore, resembles a text without an author, that a proof-reader has been correcting for more than two billion years, continually improving, refining and completing it, gradually eliminating all imperfections.’

Jacob was popularising an idea he had developed with Jacques Monod in a dense scientific paper published in 1961, which ultimately led to their Nobel Prize. Mayr had published a similar idea at around the same time, and after the appearance of Jacob’s book, the two men corresponded regularly, becoming close friends, with Mayr giving a series of lectures in Paris in 1978 and incorporating some of Jacob’s ideas into his influential book The Growth of Biological Thought (1982).

Jacob’s conception of how this view applied to the state of biology over fifty years ago can be summarised by two brief statements from either end of the book. In the opening pages, he claims, ‘The aim of modern biology is to interpret the properties of the organism by the structure of its constituent molecules. In this sense, modern biology belongs to the new age of mechanism.’ Towards the end, he argues, ‘Today biology is concerned with the algorithms of the living world.’ Half a century later, both these claims look rather overstated. Although the whole of biology did indeed become molecularised, for many researchers this was a matter of using molecular tools to reveal functions and relations, rather than using the structure of molecules (DNA, proteins, and so on) to explain, say, behaviour or ecology. Molecular reductionism has proved an immensely powerful approach, but as Jacob argues, there are interactions between higher levels of organisation—cells, tissues, organisms, and populations—that are emergent properties and cannot necessarily be predicted merely from the structure of a gene or a protein. Similarly, the enthusiasm for algorithms remains, but the complexity of living systems has proved to be greater than the relatively simple feedback-based models of cybernetics that influenced Jacob and Monod in their seminal 1961 paper and that led to the Nobel Prize. Genes, cells, and nervous systems have generally resisted simple algorithmic interpretations. Even if the power of the programme metaphor retains its strength in much of biology, it is precisely as a metaphor, not as a meticulous, prescriptive model.

The significance of all metaphors—or épistémès or paradigms—in science is that they are impermanent. They change as knowledge is acquired and as new technology allows us to imagine new things. No matter how fixed and powerful our current metaphors and frameworks might seem, we know that this will change in the future. This is the most exciting implication of Jacob’s work, one that he outlines in the closing passage of his book. Despite his confidence in his analysis and in the fruits produced by our current molecular approach to living systems—an approach Jacob did much to shape—he also recognises that this is not the final word; indeed, there will never be such a thing: ‘Science is enclosed in its own explanatory system, and cannot escape from it. Today the world is messages, codes and information. Tomorrow what analysis will break down our objects to reconstitute them in a new space? What new Russian doll will emerge?’

Matthew Cobb

Sources

Cobb, M. 2006. Heredity before genetics: A history. Nature Reviews Genetics 7:953–58.

Debru, C., Morange, M., and Worms, F., eds. 2012. Une nouvelle connaissance du vivant—François Jacob, André Lwoff et Jacques Monod. Paris: Les Rencontres de Normale Sup’.

Harvey, K. 2020. The Imposteress Rabbit Breeder: Mary Toft and Eighteenth-Century England. Oxford: Oxford University Press.

Hopwood, N. 2018. The keywords ‘generation’ and ‘reproduction.’ In Hopwood, N., Flemming, R., and Russell, L., eds., Reproduction: Antiquity to the Present Day, 287–304. Cambridge: Cambridge University Press.

López-Beltrán, C. 1994. Forging heredity: From metaphor to cause, a reification story. Studies in the History and Philosophy of Science 25:211–35.

———. 1995. Les maladies héréditaires: 18th century disputes in France. Revue d’histoire des sciences 48:307–50.

Méthot, P.-O. 2020. François Jacob et La logique du vivant: Une histoire des objets de la biology. Revue d’histoire des sciences 73:237–72.

Müller-Wille, S., and Rheinberger, H-J. 2012. A Cultural History of Heredity. Chicago: University of Chicago Press.

Peluffo, A. E. 2006. The ‘genetic program’: Behind the genesis of an influential metaphor. Genetics 200:685–98.

Wood, R. J., and Orel, V. 2001. Genetic Prehistory in Selective Breeding: A Prelude to Mendel. Oxford: Oxford University Press.

Preface

An age or a culture is characterized less by the extent of its knowledge than by the nature of the questions it puts forward. This book is a history of the questions raised about heredity rather than of the answers provided. It is a history of the efforts to ask new questions, or rather to ask old questions in a new way. And through this questioning, continuously reshaped over four centuries, we can see how the way of viewing life and the human being has gradually changed. We can see how both have become subjects of research instead of revelation.

Contrary to popular belief, what is important in science is as much its spirit as its product: it is as much the openmindedness, the primacy of criticism, the submission to the unforeseen, however upsetting, as the result, however new that may be. Ages ago, scientists gave up the idea of an ultimate and intangible truth, the exact image of a reality waiting around the corner to be unveiled. They now know they must be satisfied with the incomplete and the temporary. This approach goes against the natural inclination of the human mind, which calls for unity and coherence in its representation of the world under the most varied aspects. In fact, this conflict between the universal and the local, the eternal and the temporary, reappears at regular intervals in certain controversies—for example, in the debate between the advocates of creation and those of evolution, where arguments already used more than a hundred years ago between Huxley and Wilberforce, Agassiz and Gray, are being used again. The advocates of creation find in the smallest details of nature signs pointing inevitably to the conclusion that, in their minds, is inescapable. The advocates of evolution, on the other hand, seek endlessly in that same nature traces of events that often left none, attempting to reconstruct what they want to be not a myth but a history, a theory that evolves. This dialogue of the deaf will eternally oppose those who deny a universal and imposed vision of the world and those who cannot do without it.

Scientists have come under increased attack in recent years. They are accused of being heartless and conscienceless, of not caring about their fellow humans, even of being dangerous people who do not hesitate to discover new means of destruction and coercion and to use them. That is giving them too much credit. In any population sample there is a constant proportion of stupid people and of crooks, be it among scientists or insurance agents, writers or peasants, priests or politicians. And in spite of Dr. Frankenstein and Dr. Strangelove, catastrophes in history have been caused more often by priests and politicians than by scientists.

For people do not kill each other only for material benefit but also for reasons of dogma. Nothing is more dangerous than the certainty that one is right. Nothing is potentially so destructive as the obsession with a truth one considers absolute. All crimes in history have been the result of fanaticism of one type or another. All massacres have been carried out in the name of virtue, of true religion, of legitimate nationalism, of proper policy, of right ideology: in short, in the name of the fight against somebody else’s truth, of the fight against Satan. The coldness and objectivity so often held against scientists are perhaps more suitable than fervor and subjectivity when it comes to dealing with some human matters. For scientific ideas do not generate passion. It is rather passion that exploits science to support its cause. Science does not lead to racism and hatred. It is rather hatred that calls upon science to justify its racism. One can hold against scientists the ardor with which they sometimes champion their ideas. But no genocide has yet been committed for the triumph of a scientific theory. At the end of the twentieth century, it should be clear to each of us that no single system will ever explain the world in all its aspects and detail. The scientific approach has helped to destroy the idea of an intangible and eternal truth. This is not the least of its titles to fame.

FRANÇOIS JACOB

(Translated by Ishtar Kettaneh)

October 21, 1981

The Logic of Life

Introduction

The Programme

Few phenomena in the living world are so immediately evident as the begetting of like by like. A child soon comes to realize that dog is born of dog and corn comes from corn. Mankind early learnt to interpret and exploit the permanence of forms through successive generations. To cultivate plants, to breed animals, to improve them for food or to domesticate them, all require long experience. This already implies a certain notion of heredity and its uses. To obtain good crops, it is not sufficient to wait for the full moon or offer up sacrifices to the gods before sowing; it is also necessary to know how to select the right kind of seed. Farmers of the prehistoric era were somewhat like Voltaire’s hero, who undertook to wipe out his enemies with a judicious mixture of prayers, incantations and arsenic. Particularly in the living world, it proved most difficult to separate the arsenic from the incantations. Even when the virtues of the scientific method had become solidly established for the study of the physical world, those who studied the living world continued to think of the origin of living beings in terms of beliefs, anecdotes and superstitions for several generations. Relatively simple experiments suffice to make short work of the notion of spontaneous generations and impossible hybridations. Nevertheless, some aspects of the ancient myths concerning the origin of man, of beasts and of the earth persisted, in one form or another, until the nineteenth century.

Heredity is described today in terms of information, messages and code. The reproduction of an organism has become that of its constituent molecules. This is not because each chemical species has the ability to produce copies of itself, but because the structure of macromolecules is determined down to the last detail by sequences of four chemical radicals contained in the genetic heritage. What are transmitted from generation to generation are the ‘instructions’ specifying the molecular structures: the architectural plans of the future organism. They are also the means of executing these plans and of coordinating the activities of the system. In the chromosomes received from its parents, each egg therefore contains its entire future: the stages of its development, the shape and the properties of the living being which will emerge. The organism thus becomes the realization of a programme prescribed by its heredity. The intention of a psyche has been replaced by the translation of a message. The living being does indeed represent the execution of a plan, but not one conceived in any mind. It strives towards a goal, but not one chosen by any will. The aim is to prepare an identical programme for the following generation. The aim is to reproduce.

An organism is merely a transition, a stage between what was and what will be. Reproduction represents both the beginning and the end, the cause and the aim. With the application to heredity of the concept of programme, certain biological contradictions formerly summed up in a series of antitheses at last disappear: finality and mechanism, necessity and contingency, stability and variation. The concept of programme blends two notions which had always been intuitively associated with living beings: memory and design. By ‘memory’ is implied the traits of the parents, which heredity brings out in the child. By ‘design’ is implied the plan which controls the formation of an organism down to the last detail. Much controversy has surrounded these two themes. First, with respect to the inheritance of acquired characters. The idea that the environment can influence heredity represents a natural confusion between two kinds of memory, genetic and mental. That is an old story going back at least as far as the Old Testament. To avoid further misunderstandings with his father-in-law, Jacob tried to develop flocks of sheep easily distinguishable by their markings. He took rods of green poplar and pilled white strakes in them and set them in the watering troughs … that the animals should conceive when they came to drink. ‘And the flocks conceived before the rods and brought forth cattle ringstraked, speckled and spotted.’ Throughout the centuries, experiments of this sort were repeated ad infinitum, but not always with the same success. For modern biology, the special character of living beings resides in their ability to retain and transmit past experience. The two turning-points in evolution – first the emergence of life, later the emergence of thought and language – each corresponds to the appearance of a mechanism of memory, that of heredity and that of the mind. There are certain analogies between the two systems: both were selected for accumulating and transmitting past experience, and in both, the recorded information is maintained only as far as it is reproduced at each generation. However, the two systems differ with respect to their nature and to the logic of their performance. The flexibility of mental memory makes it particularly apt for the transmission of acquired characters. The rigidity of genetic memory prevents such transmission.

The genetic programme, indeed, is made up of a combination of essentially invariant elements. By its very structure, the message of heredity does not allow the slightest concerted intervention from without. Whether chemical or mechanical, all the phenomena which contribute to variation in organisms and populations occur without any reference to their effects; they are unconnected with the organism’s need to adapt. In a mutation, there are ‘causes’ which modify a chemical radical, break a chromosome, invert a segment of nucleic acid. But in no case can there be correlation between the cause and the effect of the mutation. Nor is this contingency limited to mutations alone. It applies to each stage in the formation of an individual’s genetic heredity, the segregation of the chromosomes, their recombination, the choice of the gametes which play a role in fertilization and even, to a large extent, to the choice of sexual partners. There is not the slightest connection between a particular fact and its consequences in any of these phenomena. Each individual programme is the result of a cascade of contingent events. The very nature of the genetic code prevents any deliberate change in programme whether through its own action or as an effect of its environment. It prohibits any influence on the message by the products of its expression. The programme does not learn from experience.

Design is another notion which has always been intuitively associated with the organism. As long as the living world appeared as a system regulated from without, as long as it was presumed to be administered externally by a supreme power, neither the origin nor the finality of living beings raised any difficulties; they remained merged with those of the universe itself. However, after the establishment of physics as a science at the beginning of the seventeenth century, the study of living beings found itself faced with a contradiction. Since that time there has been increasing opposition between the mechanistic interpretation of the organism on one hand, and the evident finality* of certain phenomena, such as the development of the egg into an adult, or animal behaviour, on the other. Claude Bernard summed up the paradox in these words:

Even if we assume that vital phenomena are linked to physico-chemical manifestations, which is true, this does not solve the question as a whole, since it is not a casual encounter between physico-chemical phenomena which creates each being