Reconstituted Chicken

Philip Kitcher

  • This is Biology by Ernst Mayr
    Harvard, 340 pp, £19.95, April 1997, ISBN 0 674 88468 X

Ernst Mayr is one of the century’s pre-eminent Darwinian evolutionists, who, in the past two decades, has published a magisterial history of biology and many seminal philosophical essays. From the title of this new book, one might expect a tour of the current state of the life sciences, made accessible to non-specialists. His selection of topics, and his way of writing about them, suggest, however, that he is less interested in communicating substantive pieces of biology than in cultivating a particular way of seeing the subject – an attitude that would appear to derive from a pre-occupation with the ideas and controversies of the past. Specifically, Mayr wants to oppose the view that biology is a science inferior to physics, to campaign for philosophical and historical approaches to the sciences that do not see all science in the image of physics, to advertise the vitality of particular branches of biology, and to defend the view that the sciences can be understood in terms of reason and progress.

On all these points, Mayr seems substantially correct. But in some chapters, he expends much effort to quash attitudes that are no longer popular; in others, he writes as if a view needs only to be stated for his readers to be convinced of its rightness. The book thus has an air of exorcising old ghosts and, in waging his campaign against them, Mayr neglects some of the most exciting aspects of today’s biology.

A central theme of the early chapters is that ‘biology is, like physics and chemistry, a science. But biology is not a science like physics and chemistry; it is rather an autonomous science on a par with the equally autonomous physical sciences.’ Since biology has been the glamour science of the last decades, few people are likely to quarrel with the first part of this, but, as Mayr is well aware, the difficulty has to do with biology’s autonomy. The enormous successes of molecular biology invite the thought that we have transcended the old idea of biology as glorified tadpole-gathering precisely because biologists have begun to deploy the concepts, principles and techniques of physics and chemistry: because, properly understood, biology is reducible to physics and chemistry.

Nobody who wants to resist reductionism believes that, besides vast numbers of molecules, living things contain some special stuff: vitalism is dead. Yet many biologists, Mayr included, have reservations about the strategy of approaching all biological questions by first asking what the ultimate molecular constituents are and how they are fitted together. Ardent champions of molecular biology, inspired by its indisputable triumphs, often see this as a residual fuzzy-mindedness that expresses itself in nostalgia for ‘whole organism’ biology. The challenge for their antireductionist adversaries is to explain how it is possible to accede to the commonplace that organisms are physico-chemical systems while rejecting the idea that biological explanation is a matter of grinding out the chemical details.

Mayr attempts to meet this challenge by defending a view he calls ‘organicism’. He introduces this by contrasting it with the reductionism he rejects: ‘The basis of organicism is the fact that living beings have organisation. They are not just piles of characters or molecules, because their function depends entirely on their organisation, their mutual interrelations, interactions, and interdependencies’. Who would disagree? Every molecular chauvinist admits that the ways in which the constituent molecules of a living system are organised are crucial. One can’t refute reductionism by the macabre argument (which I once heard offered by a professor of biology) that if a chicken is puréed in a blender you have all the same molecules but no chicken. Nor can one pick out a distinctive position by Mayr’s more tasteful celebration of organisation.

Organicism holds that some of the properties of the living system are ‘emergent’, i.e. in Mayr’s phrase, they ‘could not have been predicted from a knowledge of the lower-level components’. Everything turns here on what we take the ‘knowledge of the lower-level components’ to consist in. If we just mean ‘knowledge of the constituent molecules but not of their organisation’, then certainly living things have emergent properties, but this is irrelevant to the reductionist programme, for real-life reductionists are clear from the start that the organisation of the constituents matters. If, on the other hand, we suppose that the ‘knowledge’ includes a complete understanding of the relations among the constituents, then the claim that living systems have emergent properties needs explanation and defence.

Although Mayr fails to illuminate the murky notion of emergence, and says nothing that will cause a sophisticated reductionist to have second thoughts, it is possible to make a cogent case for the idea that biology ought to deploy various styles of explanation, including some that do not proceed from the analysis of chemical reactions among molecular constituents. To appreciate this, consider an interesting phenomenon, first noted nearly three hundred years ago. After studying London hospital records covering nearly a century, Dr John Arbuthnot concluded that, in every year, more boys had been born than girls; each year on record was a ‘male year’. Why was this? We can imagine a mad style of reductionist explanation, accessible only to a prurient deity: describe the physical and chemical circumstances of each copulation in each year; show how those circumstances determined the sexes of the zygotes that were formed; show how the physical details in each instance gave rise to a full-term pregnancy or to death of the foetus; add up the numbers of each sex born for each year. This kind of ‘explanation’ of the preponderance of male births is insane, not simply because we have no hope of occupying the standpoint of the prurient deity, but chiefly because it leaves open the possibility that the regularity is just coincidence – the physical features that affected fertilisations by X or Y-bearing sperm might have led to a majority of male births in these cases, but nothing in the rehearsal of all the physical details shows us why the same phenomenon is to be expected in other years as well.

Since R.A. Fisher’s work on selection for sex ratios, we’ve had a better explanation. Fisher pointed out that if the sex ratio in a species like ours departs from one to one at the time of sexual maturity there will be a selective advantage to producing the under-represented sex. So we can expect that there will be physiological mechanisms that work to produce approximately the same number of boys and girls at puberty. However, if one of the sexes is more liable to die between birth and sexual maturity, then that sex will have to be overrepresented at birth to ensure the later equality. Since boys are slightly more vulnerable to early mortality than girls, there’s a preponderance of male to female births (the ratio is roughly 1.04 to 1). So we understand why Dr Arbuthnot found the statistics he did.

This is a spectacular example of explanation that prescinds from the grubby details. In more mundane ways, the same point is manifest throughout biology. Whether or not they treat development in terms of precisely characterised molecular interaction, biologists working on the growth of limbs or the articulation of the nervous system are forced to employ all kinds of concepts from macroscopic biology: to invoke, for example, the geometrical relations among cells in explaining the transport of molecules across membranes. There is no pure idiom of physics and chemistry even in the heart of molecular biology, but only quite casual talk of polymerases ‘associating’ with DNA and of double helixes ‘unwinding’. The idea that many significant biological regularities can be stated in some austere physical language, let alone explained through exact physico-chemical computation, is a myth. The reductionist programme, in its strict form, fails for molecular biology itself.

All this is compatible with recognising that molecular concepts and tools play a central role in large parts of contemporary biology. Once we probe the notion of emergence, it’s possible to see both why reductionism, in its strict form, is incorrect, and why it’s the hyperbolic extension of a sensible and compelling view. Unfortunately, Mayr’s treatment of these issues is too vague to make his claims about the autonomy of biology plausible, and by keeping molecular biology in very soft focus, the bogey of reductionism continues to loom. Even worse, his failure to incorporate molecular biology into his book means that the vast majority of biologists will not recognise the subject as they practise it. Some may want to add a question mark to his title.

Before reviewing the parts of biology he loves, Mayr interposes some philosophical chapters, designed both to bring out the importance of biological examples for understanding science and to defend the ideas of reason and progress in science. On the first score, he has a simple story to tell. Around mid-century, philosophy of science attempted to characterise the notions of scientific test, scientific confirmation, scientific explanation and scientific theory by using the tools of mathematical logic and applying them to examples from physics. This led to a picture of science that was at best distorted and at worst inaccurate. More recently, philosophers have taken biology seriously, and this has led to salutary revisions of older philosophical proposals, although Mayr seems to think that there is still important work to be done.

There is something to this story: the pre-occupation with biology (and with a range of other sciences) has surely enriched recent philosophy of science. However, on matters of detail, Mayr is frequently untrustworthy. ‘The rigorous approach of the logician,’ he claims, is not suited to probabilistic phenomena, a charge that will come as a surprise to the numerous philosophers who have been doing careful work on probabilistic phenomena for decades. When we read that ‘most philosophers seem to be quite reluctant to provide definitions,’ the natural response is to point to the scores of books and articles that strive to give precise explications to concepts, often in what strikes outsiders as an anal-retentive way. Mayr’s charge that ‘the classical philosophy of science has made curiously little reference to the important role of concepts in theory formation’ seems belied by the fact that one of the influential classical monographs – C.G. Hempel’s Fundamentals of Concept Formation in Empirical Science, which began a significant tradition – was devoted to precisely that subject. And when he claims that all the scientists he knows are scientific realists, firmly believing in the unobservable entities of the theories they adopt and extend, this seems only to show that Mayr talks to biologists and not to quantum physicists or superstring theorists.

Professional philosophers are likely to be irritated by the apparent lack of connection between Mayr’s claims and the literature he aspires to discuss (the examples I have cited are only a small sample), as well as by the confidence of his pronouncements. Far more significant, however, are his attempts to respond to scepticism about scientific progress – and here he is more successful.

In recent years, several prominent scientists have become alarmed by the contributions of outsiders who have studied the practice of the sciences. The current ‘science wars’ are largely concerned with claims that scientists ‘construct reality’, that the prime motors of scientific change are scientists’ ‘interests’ or their ability to ‘enrol allies’, that standards of scientific evidence are relative, that the notion of scientific truth is incoherent, that we cannot sustain any idea of scientific progress, that traditional Western science is imperialistic, and rocentric and bourgeois, that Newton’s Principia should be understood as a rape manual, and so forth. The principal villains seen as promulgating these doctrines are scholars like Harry Collins, Sandra Harding, Bruno Latour, Simon Schaffer and Steven Shapin. Now whether these alleged enemies have anything in common, and whether there is a genuine package of claims about science that count as constructivism or relativism or Post-Modernism are serious questions that deserve careful analysis. At present, however, there is a pronounced tendency to divide the world into the True and the Good, and the Forces of Darkness – and to start firing.

At first sight, Mayr’s engagement with the debate seems quaint and unpromising, as if he hadn’t heard of recent developments. His target is Thomas Kuhn, and he wants to rebut the claim that the history of science is punctuated by Kuhnian revolutions. Kuhn’s famous Structure of Scientific Revolutions contains a final, worried, chapter, in which he tries to find a viable conception of scientific progress. Convinced that he can discern in the history of science ‘no coherent direction of ontological development’, Kuhn rejects the idea that science progresses by the replacement of false views of nature with true ones (or ones that are close to the truth), and he even suggests that any notion of truth as correspondence to nature is incoherent. These arguments are directly pertinent to the ‘science wars’, for, despite Kuhn’s explicit repudiation of some of the scholars who claimed to be elaborating his views, notably relativist and constructivist sociologists of science, they are the starting point for much contemporary discussion. When scientists express doubts about the idea that the world they describe is a social construct, they are often told, with apparent authority, that ‘Kuhn has shown that’ their old-fashioned notions of truth and progress are incoherent. (Kuhn himself was far less sure that he had established the theses that are flourished in his name.)

Whether or not Mayr intends his critique of Kuhn to bear on present squabbles is unclear. Nevertheless, by focusing on some important episodes in the growth of biological knowledge, he goes to questions that are at the root of those controversies. Mayr reminds us of the history of advances in cell biology, systematics and evolutionary theory, indicating a pattern that persists through doubts, debates and uncertainties, in which there seems to be a gradual accumulation of biological belief: the kind of pattern that prompted John Maynard Smith to remark, in a review of one of Mayr’s earlier books: ‘Unfashionable though it may be to say so, we really do have a better grasp of biology today than any generation before us, and if further progress is to be made it will have to start from where we now stand.’

Mayr’s history in this book is much more condensed than that to be found in his monumental Growth of Biological Thought, inviting the charge that it involves a naive rewriting of the past, seen as directed towards the present. Mayr’s longer historical studies, and those of the many historians of biology whom he has profoundly influenced, constitute an ample rejoinder to the accusation. They show how contemporary conceptions gradually emerged out of confusion and controversy, how, if we confine ourselves to relatively short time periods, there may seem to be no consistent direction in the change of biological ideas, but that a general trend emerges from studies of the longue durée. Those historians who are convinced that we can make no sense of the idea of scientific progress might set themselves the task of explaining the illusion of cumulative advance, so well documented in Mayr’s Growth of Biological Thought (and more briefly here).

The obvious way to approach that task is to turn from the biological to the physical sciences and recall two important episodes. From Ptolemy to the early Renaissance, astronomers thought they were making progress in understanding the solar system. As the years went by, their models became more complex but their predictions were more accurate. Yet, from our post-Copernican point of view, they were profoundly mistaken: the earth was not, as they took it to be, the centre of the universe. Couldn’t we be in the same predicament with respect to the parts of biology that Mayr celebrates? The question can be sharpened by considering a second piece of history. From the 18th century to the dawn of the 20th, scientists articulated Newton’s ideas to produce ever more powerful explanations and predictions of physical phenomena – indeed, Lord Rayleigh, addressing the British Association in 1900, felt the need to apologise for the fact that physics was nearly finished. Five years later, Einstein and Planck launched a revolution that would overthrow Newtonianism. Couldn’t the same fate befall Darwin, or Morgan, or Mayr?

Although these examples are frequently assimilated, they need to be treated differently. Post-Copernican astronomy has broken in all kinds of ways with the Ptolemaic tradition, but we can take comfort in the fact that that earlier tradition was not particularly successful: thus, if the concern is that an apparently successful scientific tradition can be overthrown by something radically different, the right response is to emphasise the differences between the successes of current sciences (such as biology) and those achieved by medieval astronomers. By contrast, nobody ought to deny that Newtonian physics was strikingly successful. In this instance, the sceptic goes astray by emphasising the discontinuities between Newton and post-Einsteinian physics: the much-derided textbook connections between Newtonian concepts and their relativistic successors offer a much more accurate view of the relations between stages in the history of physics than Kuhn’s famous remarks about Newtonian and Einsteinian physicists ‘living in different worlds’.

Mayr’s tour of various parts of biology is not only a readable introduction to the fields of evolutionary theory, systematics, (some of) ecology, and (some of) developmental biology, but an advertisement for the range and power of the biological sciences. As such, it deepens and extends his case for the idea that ‘we are making steady advances in our understanding of nature,’ a point Mayr rightly-views as being shared by most practising scientists. Since many of those responsible for the relativist, constructivist and Post-Modernist pronouncements about the incoherence of the ideas of progress and objectivity are, to put it gently, somewhat shy about getting involved with the details of scientific work, one of the best antidotes is to provide a lucid summary of contemporary ideas and achievements. Mayr’s authoritative and gracefully written summaries are excellent – as far as they go.

As Mayr himself acknowledges, molecular biology is too important to go unmentioned, but his glancing references to molecular discoveries are too few to provide an accurate picture of the science that over 95 per cent of today’s students and researchers learn and practise. Indeed, there are some extraordinary omissions. Mayr devotes a chapter to developmental biology, but, apart from remarks about results with nematodes and fruitflies, he offers no hint of the ways in which the subject has been transformed in recent decades. Interested readers will learn nothing about the study of regulatory mechanisms (begun by François Jacob and Jacques Monod) or the pioneering experiments of Christiane Nüsslein-Volhard and her associates, rewarded with last year’s Nobel Prize for Medicine. In those experiments, Nüsslein-Volhard showed how to identify molecules and molecular interactions responsible for the early segmentation patterns of fly larvae, exposing, for the first time, the way in which the fundamental structure of a multicellular organism is generated. That has opened the way to future research which will identify the molecular mechanisms underlying development, not only in flies but also (we hope) in vertebrates. It is surely as important as anything Mayr does mention.

Even within evolutionary theory, his home territory, Mayr is highly selective. Although he offers brief surveys of sociobiology and of group selection, he does not discuss the key theoretical work that has fuelled these disciplines – William Hamilton’s treatment of kin selection and John Maynard Smith’s evolutionary game theory, for example. Mayr’s biological tastes do not run either to mathematics or to molecules. Today’s biology is dominated by both.

Moreover, the mathematics, and especially the molecules, are crucial to the most spectacular successes of the biological sciences. Faced with the worry that these might suffer the same fate as medieval astronomy, one might well ask whether the Ptolemaic tradition (with its struggle to fit planetary motion to ever more cumbersome models) could do anything similar to the routines of today’s biological laboratories: producing bacteria that will serve as factories for desired proteins, manufacturing mosaic flies with specified characteristics in specified tissues, breeding mice with analogues of human diseases. Socially conscious scientists and science critics may disapprove of some of the projects to which biology now lends itself – but that is a sort of compliment to its power. The view that biology doesn’t tell us the truth about nature is, ironically, a bar to the proper kind of critical thinking about the life sciences. Precisely because biologists get significant things right, their findings are open to wise use or potential abuse. At least part of the humanistic study of science, whether undertaken by historians, philosophers, sociologists or scientists themselves, ought surely to be devoted to sparking public discussion of the tools that contemporary biology provides.