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Normal development

Introduction and clarification of terms

The aim of this paper is not to present anything radically new. Rather it is to propose that the concept of normal development be given serious philosophical and historical attention. I take up a lot of threads that have been started by others here and tie them together around the pole of normal development. I hope that the claims I present here will function as much as a provocation for further work as consciousness raising as to the importance of normal development as an issue to deal with.

Here is what I plan to do in this paper: first I will briefly clarify what is meant by development, and what is meant by normal. Then I will outline where at least normality in biology has been dealt with in the scholarly literature, and then outline some of the uses of the term normal development in the modern scientific literature.

I will then outline why exactly I think the way normal development is used in the scientific literature is problematic, and then examine two perspectives with which normal development can be understood. I will then discuss some alternative approaches in order to deal with the diagnosed problems.

First of all, a clarification is in order – what is development?

There is far more to this question than there is space to pursue it here, but generally, and I believe uncontroversially, speaking, we can say that it is what goes on in an organism between two points in time. This can be between the point at which the egg is fertilised and death, or it can be the condition of the organism between any other points of interest. Development can be local, for a particular structure or function, or it can be global, the entire organism. Development, and the biological investigation of it, is concerned both with change and stasis of an organism over a specified period of time.

We can say, following this discussion, that developmental biology is the science of the phenomenon and phenomena of development.

It has been said that the word normal, when used in science, can only be used in the biology or psychology (Canguilhem, 2008). I will not pursue this particular line of thought here, but I will pick up on possible different ways we can speak of normalcy within the biological sciences in the section on further implications later.

There is more than one way of being ‘normal’. Normality or normalcy can be entirely descriptive, or it can be entirely normative, or a mixture of the two. If normality is entirely descriptive, it is an expression of the scientists’ expectations and how what they have observed relates to those expectations. Here we are in the realm of typicality and frequency. Normal development is what they would expect to find given the internal and external conditions (i.e. the organism itself and the situation, circumstances or milieu it finds itself in, or the scientist has carefully ensured it is in). If the scientist has a number of embryos, and gives the vast majority of them ‘ideal’ conditions for

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development, measurements will be taken, tables constructed and perhaps more importantly expectations will be shaped.

Now, if the embryos of the same organism are then given experimental manipulations – perhaps the destruction of one of the cells, exposure to a virus, exposed to conditions to which they would not typically be exposed (high pressure, high or low temperature, chemicals known to cause deformities or defects in other organisms) – the consequences of this will be measured against the normal development. If it falls, according to the tables (and see Hopwood, 2005 and 2007, for a detailed historical account of the construction of such tables and plates, and the way in which they were part of embryologists constructing development itself) and the scientist’s judgment, within the range adjudged to be normal, it will be deemed that normal development has occurred. Otherwise, it will be deemed to be abnormal development. I will be assumed that in the case of normal development the manipulation or insult will be deemed to be insignificant. This can lead to certain conclusions about the nature of development, but also the nature of the insult to which the organism was exposed.

What is interesting here is that the term normal development is frequently used without definition, is employed implicitly rather than explicitly, and has had little scholarly attention paid to it. I propose that this needs to be remedied and intend to make a tentative attempt to do so by attacking a number of issues relating to normal development. The fact that it is a term used so implicitly by scientists renders it interesting in a different way to concepts such as ‘the gene’ which are defined formally by scientists who feel the need to define it, but is used in practice quite differently. Its sheer invisibility renders it stable, like the stable genes used to track phylogenetic changes, but also potentially anachronistic when wider changes occur in the science in which it is used. It is in danger of being the cuckoo in the nest, tying an altered science down to some concepts, perspectives, orientation and bias from which it is trying to escape.

On Normal Development

In the scholarly literature:

I have been able to find little on normal development. There are papers on normality and normativity (much in the philosophy of medicine of course), but this is all. For example two papers which I have used for this presentation, ‘Normal People’ by John Dupre (1998) and ‘Against Normal Function’ by Ron Amundsen (2000), speak of normality and normativity, and the work, as we shall see, is of relevance for a discussion of this sort, but they do not specifically tackle the issue of normal development. In broader textbooks (e.g. “Sex and Death” by Sterelny and Griffiths (1999), and “Philosophy of Biology” by Garvey (2007), the issue is not touched on at all, save for a mention of the norm of reaction. More specifically, texts largely concerned with development (see Robert, 2004 and Burian, 2005 for instance) do not question or pick up on the killer phrase ‘normal development’ either.

Of the work that Dupre has done on the normal, he identifies nicely the “ambiguity in the concept of normality” (Dupre, 1998: 225) in that it can “be thought of simply as the typical or common” (ibid) or “sometimes intended normatively or evaluatively” (ibid). He notes that, applied to humans at least, “the concept of normality is almost invariably normative” (ibid) and that “our interest in normality is

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most often driven by a concern to identify its absence, abnormality” (ibid). I would argue that that the former is true in biology – the normality is almost invariably normative – normal development is what should happen in the development of this particular organism. But I would argue that in strictly biological matters the latter is on its head – firstly in seeking to create standardised populations of organisms for experimental use, the need is to identify abnormality, and the conditions that give rise to it, in order to standardise properly. In many cases, this may mean using organisms that are uniquely strongly canalised in their developmental pathways, and largely inured from any environmental influence in their development. It may mean breeding this characteristic into the population. Secondly, in typical developmental and genetic experimental practice, measures to try and create the abnormal are there in order try and explain the normal – lets knock out that gene to see what role it (and more important its products) play in development by finding out what does and does not happen in its absence. More gross experiments have been conducted over the last 130 years as well.

In introducing and applying the concepts of ‘intrinsic’ and ‘relational’ capacities Dupre (1998) presaged the work of Amundsen on ‘normal function’. Intrinsic capacities are those such as the “capacity to move my fingers in more or less controlled and accurate ways” (Dupre, 1998: 229). “Only neurological and physiological damage to my body will remove this ability” (ibid). Relational capacities on the other hand includes the “ability to send an e-mail” (ibid) which one has only “in so far as I have access to the instruments of a complex technology of a kind with which I am sufficiently familiar” (ibid). Amundsen argues, I believe in this vein, though he does not use the terms intrinsic or relational. He distinguishes, when considering a function, between the “level of performance” (Amundsen, 2000: 36) of the function and the “mode of its performance” (ibid). He follows this (not immediately), by noting that “Development yields adults that function, but not adults that function identically” (Amundsen, 2000: 39), and that this “Functional diversity is a product of developmental plasticity” which exhibits for him a goal-directedness (ibid). For Amundsen, it doesn’t matter developmentally whether a capacity is intrinsic or relational, but that the capacity is there. And given the plasticity of development (there will shortly be a definition of this), not only are the intrinsic capacities not set in stone, neither are the relational capacities. In fact, I would suggest that as well as his argument, which I endorse, about the need to focus on enriching the relational capacities when it comes to humans with impaired intrinsic capacities, I would suggest that development could be about the shaping of intrinsic capacities to be able to take advantage of, or even create, relational capacities for enhanced or maximal functioning.

Georges Canguilhem offers, in his interpretation of the work of Kurt Goldstein, a similar take. He states that “A norm…must help us understand concrete individual cases. It is thus worth less for its descriptive content-as a summary of phenomena, symptoms on which a diagnosis is founded-than for its revelation of the total comportment of an organism, which has been modified in the sense of a disorder, in the sense of the appearance of catastrophic reactions. An alteration in the symptomatic content does not appear to be a disease until the moment when the being's existence, hitherto in equilibrium with its milieu, becomes dangerously troubled. What was adequate for the normal organism, in its relations to the environment, becomes inadequate or perilous for the modified organism. It is the totality of the organism that reacts "catastrophically" to the milieu, as it becomes henceforth incapable of actualizing the possibilities of activity essentially belonging to it.” (Canguilhem, 2008: 129).

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We can find discussions of the use of normal stages in developmental biology in Hopwood (2005, 2007) and Love (2009). In Hopwood we see an historical account of the genesis of normal plates and tables created and used in developmental biology, locating the origins these in concerns and work about the relationship of ontogeny to phylogeny in the late nineteenth century (Hopwood, 2007). The scientists engaged in this work, and in debates about the normal plates, their construction and use, were fully aware of the immense variability they observed and worked with. Hopwood stresses that these tools could be put to use to suit different research agendas, and indeed, although one of the original uses for which they were designed and put to work on – the study of embryological variation, they were later put to use to abstract away the variation in the construction of normal stages. This is what Love picks up on in his discussion of the modern use of normal stages in evolutionary developmental biology. There is a discussion of Love’s work in a later section.

Oyama (2000) is probably the text which has inspired many of the thoughts and ideas that are contained within this piece, but from which I can extract so little specific argument concerning the ‘normal’. There are plentiful references to normal and abnormal genes, environments, phenotypes, and so on, and a recognition that the normal can be descriptive or normative. These considerations of normal are never more than asides or parts of arguments concerning something else however, and Oyama adopts a generally sceptical tone (with plenty of scare quotes) towards the normal or abnormal (or pathological), for instance referring on one page to ‘considering’ a developed form or function normal, of ‘judging’ something to be pathological (Oyama, 2000: 148).

In the scientific literature:

Let us look at some examples in the scientific literature. In a standard textbook on ‘Insect Development’ (Gilbert ed., 2009) we find the following references to normal or abnormal development (all references are to chapters in this text):

“in normal development, only Scr patterns the first thoracic segment.” (Robertson and Mahaffey, 2009: 27)

“the involvement of ubiquitin regulation of proteolysis and the mitochondrial abnormalities suggests an important relationship between pathology and PCD in normal development” (Fahrbach, Nambu and Schwartz, 2009: 187)

“the normal developmental increase in basal ecdysteroidogenesis was inhibited” (Rybczynski, 2009: 213)

“Parasitism by this species elevates dopamine levels in the nerve cord and hemolymph, slows normal development, and delays pupation of the host” (Goodman and Granger, 2009: 328)

“contradict the hypothesis that a JH-free period is required for further normal development” (Goodman and Granger, 2009: 360)

“If flies carrying a null mutation in Met can undergo seemingly normal development and limited oogenesis” (Goodman and Granger, 2009: 370)

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“at an inappropriate stage the hormonal imbalance would force the insect to go through abnormal development leading to mortality.” (Atkinson, O’Brochta and Robinson, 2009: 680)

We can see in all these examples that normal development is taken to be a particular and singular course that the organism during ontogeny traverses, that can be slowed, progressed further along (or retarded) or depart from the course leading to abnormal development. Note that ‘normal development’ here can be used as a synonym for both ‘typical’ and ‘proper’ development. Disturbances of the normal course of development lead to abnormality which is explicitly linked with mortality. In the use of language, these accounts allow expectation to bleed into the normative. The course of development which the organism would have displayed but for X should have taken place and X was responsible for it not taking place.

’Principles of Development’ (Wolpert et al 2011) is another standard work. The authors adhere to the view that “All the information for embryonic development is contained within the fertilized egg” (Wolpert et al, 2011: 29) and that “the genome contains a program of instructions for making the organism” (ibid). It is perhaps inevitable then that the first major example provided of ‘abnormal development’ is one in which “development goes awry” due to mutations in genes (Wolpert et al, 2011: 28). So to some of the (not exhaustive) references to normal development (I have excluded the numerous references to ‘abnormal development’ for the purposes of concision):

“For normal development it is essential that maternal Hunchback protein is absent from the posterior region” (Wolpert et al, 2011: 50)

“both blastomeres of the two-cell mouse embryo can give rise to normal embryos if separated…normal development can still occur even after cells are removed or added to a preimplanatation embryo…in normal development, individual blastomeres in early embryos have different developmental properties and fates” (Wolpert et al, 2011: 138)

“If part of a future limb region is removed, the remaining part can still regulate to develop a normal limb.” (Wolpert et al, 2011: 209)

“Most of the cell divisions in normal plant development occur within meristems” (Wolpert et al, 2011: 265)

“both the maternal and the paternal genome are necessary for normal mammalian development…both are required for the normal development of the embryo and the placenta.” (Wolpert et al, 2011: 340)

In this standard account we again see normal development spoken of as an ordered, set process which can be diverged from due to various factors, including genetic mutations or the presence or absence of certain molecules, and which requires the presence of normal factors such the genomic contributions from male and female. We also see a reference to the normal as typical, expected or ideal (as in the quote from page 209).

But what of works that can be classed as exhibiting some of the traits of the ‘new developmentalism’? One such is ‘The Development of Animal Form’ (Minelli, 2003). In this we find the following references to normal and abnormal development:

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“which in Drosophila is required for normal development of the head and thorax” (Minelli, 2003: 43)

“Consequently, developmental processes which in normal development occur successively, now took place simultaneously, and vice versa. This strong disturbance notwithstanding, the developmental processes resumed normal pace after the temperature gradient was switched off. Thus, this egg’s development demonstrated robustness, with extreme desynchronisation during early development causing no problems on the segment pattern of the resulting embryos.” (Minelli, 2003: 59-60)

“In more complex organisms, such as vertebrates, in which the regenerative power is primarily limited to the appendages (limbs and tail), regeneration may recapitulate normal development.” (Minelli, 2003: 131)

“A correct cell size, however, is not simply a mechanical requirement for normal development.” (Minelli, 2003: 133)

“as it is first manifested in extraembryonic tissue which is essential for normal development of anterior structures” (Minelli, 2003: 136)

“In the leech Helobdella robusta, normal development of the segmentally repeated cell clones derived from one of the blast cells does not depend on signals from adjacent clones derived from the other blast cells” (Minelli, 2003: 215)

“xenoplastic grafts often give rise to partially equivalent structures, sometimes even in organs that in normal development do not seem to be homologous” (Minelli, 2003: 229)

What we see here again is an overriding concern for the typical course that development should take in particular organisms, and the states which pertain at particular points in that normal course of development. We also see normal development referring to the state of an end-point of development in the quote from page 43.

The developmental biologist Scott Gilbert has dealt with many philosophical and historical aspects of development – what has he to say of ‘normal development’? He uses the term normal development in much the same way as the previously cited authors – e.g. “normal course of development” (Gilbert, 2010: 403). But despite including chapters (in Gilbert, 2010) on ‘Medical Aspects of Developmental Biology’ and ‘Developmental Plasticity and Symbiosis’, he doesn’t at any point go beyond some of the fascinating cases he presents (and which is hinted at by the heading of one of the sections in the latter chapter, ‘The Environment as a Normal Agent in Producing Phenotypes’) which outline the dynamic aspect of development in producing norms of reaction and polyphenisms.

In Gilbert and Epel (2009) we see a reference, again in a section heading, to “Plasticity is a Normal Part of Development” (Gilbert and Epel, 2009: 6), in a chapter entitled “The Environment as a Normal Agent in Producing Phenotypes” (Gilbert and Epel, 2009: 3), in a part entitled “Environmental Signals and Normal Development” (Gilbert and Epel, 2009: 1). There is a reference early in this chapter to phenotypic plasticity which “was well known to nineteenth-century embryologists, who showed that different environmental conditions produced different phenotypes during normal development” (Gilbert and Epel, 2009: 6). Shortly after this it is concluded that “the

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same genotype can generate different phenotypes depending on what cues are present in the environment, allowing the embryo to change its developmental trajectory in response to environmental input” (Gilbert and Epel, 2009: 10). While plasticity in development is usually beneficial to the organism, or adaptive, “there are times when plasticity is maladaptive – either when environmental cues alter development in a pathological manner, or when there is a mismatch between the phenotype induced by the embryonic environment and the environment experienced by the organism later in life” (ibid).

So in this first chapter we see the possibility of a change in developmental trajectory, which is usually beneficial, but sometimes deleterious. In the following chapter we can see some very suggestive references to “mechanisms by which environmental cues can instruct changes in normal development” (Gilbert and Epel, 2009: 37) and that “during normal development, differences in cytosine methylation are critical in telling a nucleus which genes can be expressed, and which genes are expressed determines what type of cell it will become” (Gilbert and Epel, 2009: 43). Here we see a development of the only previously suggested idea that normal development itself might be changeable, that unlike the previous references to particular courses of development, normal development might be more akin to a transport network to get you to various cities rather than a linear route from A to B. There is much more to Gilbert and Epel’s conception of normal development than can be found in the more ‘standard’ biological works. This can be seen as a consequence of Gilbert’s engagement with new thinkers about development, particularly those associated with developmental systems thinking or theory, though Gilbert does not class himself as an adherent of these new perspectives. But he does not go beyond what I have quoted here. Indeed in the ‘Coda’ chapter, “Philosophical Concerns Raised by Ecological Developmental Biology” (Gilbert and Epel, 2009: 403-417), these issues are not picked up at all.

What of other writings on development? Well, one text, which is a magnum opus very much part of and driving some of the reorientation in biologists’ thinking about development, talks about normal development so: “normal development often depends on specific information and materials from the environment, in addition to those from the genome” (West-Eberhard, 2003). So here the normal course of development is dependent on things which are either external to, or a special part of, the organism. Specificity is essential, implying that there are particular genomes that can aid normal development, and particular environmental conditions.

An earlier work, a textbook entitled ‘Developmental Psychobiology: An Interdisciplinary Science’ (Michel and Moore, 1995) is the only scientific text I have been able to find that really questions this notion of normal development. Certainly, references can still be found to a study being an “excellent illustration of the fusion of maturation and experience in normal development.” (Michel and Moore, 1995: 114) and “the normal development of the olfactory bulb requires olfactory input” (Michel and Moore, 1995: 116). But we also can see the following concern with process rather than course: “the cellular interactions underlying mouthpart development in newts and frogs are equally capable of regulating a normal developmental process for either balancers or suckers” (Michel and Moore, 1995: 281). Is there an attempt to make the notion of normal development more explicit than unstated though? Yes there is, and it’s rarity in the literature means that the section is worth quoting extensively:

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“At present, normal and abnormal or pathological are not scientific concepts (Tiles, 1993).

…

These investigators note that the meaning of abnormal is almost entirely derived from the meaning of normal. Consequently, understanding normal development is a prerequisite to understanding abnormal development. However, the various definitions of normality (e.g., socially and culturally acceptable, statistically frequent, socially and culturally typical, traditionally and authoritatively defined as healthy) depend heavily on an intuitive sense rather than on a systematic, empirical investigation of normal development.

Intuitive definitions of normality maintain certain assumptions about the individual, the environment, and the types of processes that create the individual's behavioral repertoire (including the symptoms characteristic of abnormality). These assumptions are not supported by modern animal research conducted from a natural history orientation. They have been called into question by modern advances in developmental psychobiology, as well.

One implicit assumption is that the course and outcome of development are universal and immutable. Of course, those who hold to this idea acknowledge that certain factors can alter the rate of progression or the final level achieved, but these alterations are limited and circumscribed by intrinsic conditions present at the outset. This view leads to research that is focused on observed regularities and that neglects contextual differences. Thus, normal is defined as the typical rate of progression through common universal patterns that results in a typical outcome. Factors that alter the rate or end point of progression result in deviations from the typical and are considered the causes of abnormal development. This is at variance with the understanding of development achieved from a natural history orientation, which incorporates contextual factors into the explanatory system (see Lerner, 1991).

…

The assumption that normal development consists of a universal, relatively immutable, developmental sequence is challenged by the discovery of both equifinality, that is, the same psychological ability may arise from quite different developmental pathways and processes, and multifinality, a specific developmental pathway or process does not invariably result in the manifestation of one specific ability. These two phenomena, which have been identified frequently in the development of animal behavior and used recently in human development (Fischer, Knight, & van Parys, 1993), challenge intuitive concepts of abnormality and its treatment.” (Michel and Moore, 1995: 411-412).

They go on to comment that “The concept of unusual, like that of abnormal, must not be taken merely in the statistical sense but in terms of what constitutes a perturbation for the equilibrium of the individual environment system (Gollin et al., 1989). Furthermore, novel adjustments need not be

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pathological, but may represent adaptive changes in the system. …it is not possible to point either to the individual or to the environment in isolation from the other and identify normal or abnormal elements either in individual functions, capacities, or abilities, or in the range of resources or deficits in the environment. These elements have to be considered in relation to other parts of the system.” (ibid). Their prescription also includes the adherence to a ‘natural history’ orientation to biological research and the injunction that “Whether for developmental research or for deciding on clinical strategies, individuals must be examined to determine exactly what pattern of match-mismatch exists between their capacities and the characteristics of the available environment” (Michel and Moore, 1995: 414).

There are a couple of limitations with Michel and Moore’s approach however. One is that it is explicitly related to the development of behaviour, their examples in this section including grief and dyslexia. As can be seen from the earlier examples from this work, once they descend to levels ‘below’ the behavioural, they cannot avoid ‘normal development talk’ in the sense that they identify as descriptive of typicality and normative in nature. They do not offer a way out on this issue – is talk and use of normal development to be scrapped, or is it to be reformed? If it is to be reformed, the prescription for change cannot be found amongst their other prescriptions and exhortations.

Might we expect a similar critique from Gilbert Gottlieb, one of the standard bearers of developmental psychobiology? In one of his books that I examined, there are only hints, albeit instructive ones. The first is a quote from Hans Driesch that "there are more morphogenetic possibilities contained in each part than the observation of the normal development can reveal" (Gottlieb, 2002: 64). The second is in a quote from Gavin de Beer which refers to “’normal' developmental responses” (Gottlieb, 2002: 96) as well as “a departure from normal development” (ibid). We can also see a reference to “usual or normal developmental conditions” (Gottlieb, 2002: 175). So in what way are these examples instructive? Well first of all, it is perhaps telling that he himself only uses the term ‘normal development’ once. This he uses in to describe typical conditions rather than states. However, he also quotes Driesch and de Beer (without criticising their use of the term) who offer up normal development as typical course of development (Driesch and de Beer) and the reactivity and responsiveness of the organism (de Beer). It is however worth pointing out that this particular text was originally written before the Michel and Moore textbook.

Disappointingly, in a more recent collection on developmental psychobiology (Blumberg, Freeman and Robinson eds., 2010) there is abundant use of the term normal development, the only occasion in which it was brought into question was the placing of inverted commas around the normal (thus: ‘normal’) part of the term (Ardeil, Rai & Rankin, 2010: 288, in: Blumberg, Freeman and Robinson eds., 2010).

Why Is ‘Normal Development’ A Problem As It Is Currently Employed?

Introductory discussion

There are two reasons why I believe that the term ‘normal development’ is problematic in its usage in biological science. Firstly, normal development is a term which represents a multitude of meanings that are not just different, but I would argue mutually exclusive.

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I also believe that it is problematic because it increasingly doesn’t reflect the way that an increasing number of biologists think about development. Moving away from a conception of development as a single path along which every organism moves, directed by something internally – an agent acting on brute matter to organise it sequentially, with the environment as a permissive, background condition – biologists are considering more and more the dynamic nature of development, of the ability of the developing organism to accommodate itself to the changing conditions that pertain throughout its life. Some of the main ways in which ‘normal development’ is understood betray certain assumptions about what development is and how it can be approached scientifically (the ontological underpinning the epistemic recapitulation of the flawed ontology) that have been increasingly under attack for good reasons. If we are to accept these critiques and advance a new way of thinking about development (though it’s worth emphasising that this new way is in fact older than myself) then we must re-examine the use of the term normal development. This is not a call for abolition, as if such a call would be heeded, but for critical examination, and perhaps the adoption of more careful terminology more closely in tune with the intentions, thinking and practice of the user of such terminology (writing it or reading it).

New understandings and interpretations of development – plasticity and robustness:

Two of the main ways in which the organism can act dynamically over the course of its development lie under the terms plasticity and robustness.

Plasticity has been defined as “the ability of an organism to react to an internal or external environmental input with a change in form, state, movement, or rate of activity” (West-Eberhard, 2003: 33). It is thought that “Both continuous and discrete plasticity are products of condition-sensitive switches … [where] a switch between alternative phenotypes or between successive events in a developmental pathway is a point where there can be plasticity in whether or not a trait is expressed or a process continued” (West-Eberhard, 2003: 36). Examples of this plasticity include the “hypertrophy of muscle, bone, and callous tissues that are used or subjected to stress, and the atrophy of unused tissue” (West-Eberhard, 2003: 40), radically different stable phenotypes within the same species depending on conditions during development. The example of the polyphenism of water fleas Daphnia depending on the presence or absence of predators is a classical demonstration of this (Gilbert and Epel, 2009: 27). Heterophylly in plants is another example, for instance with a species of clover, which can develop very different forms of leaves depending on whether that part of the plant is submerged or not (Lin, 2002).

Phenotypic accommodation can be defined as “adaptive mutual adjustment among variable parts during development without genetic change” (West-Eberhard, 2003: 51). Some examples of this with humans with no functional consequences are different forms of stomachs, and arterial branching patterns. More remarkable and exceptional are examples where four-legged animals, for whatever developmental reason, early on have only two limbs able to develop. In those cases are exhibited “profound changes in the skeleton and muscle insertions compared to a normal” animal (West-Eberhard, 2003: 51).

On the other hand, robustness has been defined as “the processes that lead to a relatively invariant outcome” (Bateson and Gluckman, 2011: 29) “in relation to insensitivity or resistance of the phenotype to” perturbations, be they environmental, genetic or otherwise (ibid). This definition

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hints at stability of the phenotype, but hints in a number of places more of a stability of type (species typicality is invoked) or of maintenance of characteristics, traits and functions. It is clear despite the rather static definition the authors intend a rather more dynamic conception of robustness, one in which robustness is intimately and inextricably tied up with an organisms developmental plasticity. A number of processes are cited as those responsible for robustness, including insensitivity to environmental (and other) signals or inputs, constraints (historical such as the basic body plan organisation being laid down early in development, or to do with availability of materials such as nutrients or hormones as in the case of the size of babies being determined by the size of the mother), attractors and redundancy in pathways (ensuring many different ways to end up at the same end-point – equifinality), repair mechanisms, regulation (synchronic in the more physiological sense of homeostasis, diachronic in the more developmental sense of homeorhesis – where the set point can change over the course of development), canalisation and the differential survival of systems and components (the neuronal pruning in foetuses and infants for example) (Bateson and Gluckman, 2011: 22-29).

Gluckman and Bateson make the argument that plasticity and robustness are fundamentally entwined processes, outlining the evidence (see Bateson and Gluckman, 2011: 46-62 for this) for the claim that “a range of alternative anatomical structures may be generated by conditions in early life and…[that] plasticity is governed by robust rules such as those used for detecting causality in the environment” (Bateson and Gluckman, 2011: 62). They urge rejection of “a hard and fast distinction between robustness and plasticity” (ibid). As an aside, it is interesting to note that part of this rejection is the aim of cutting across objections that the anatomy of organisms is robust and the behaviour plastic. This is a particularly acute point, given that so many of those outlining new thinking about development are predominantly biologists concerned with behaviour. This is certainly true of Bateson and Gluckman, it is also true of Gottlieb and Oyama. Further support for Bateson and Gluckman’s position can be found in a review on ‘Biological Robustness’ (Kitano, 2004), where it is observed that certain phenomena responsible for biological robustness – redundancy and heterogeneity for example – are in fact synonymous with what we might call phenotypic plasticity (Kitano, 2004: 828).

I should emphasise that there are acknowledged to be limits to the plasticity and robustness of living and developing organisms. That said, as Love (2009) argues, given the practice of biologists, particularly with regard to developmental biology conducted with model organisms, the extent of plasticity in living organisms has not been appreciated as yet. I will deal with some of Love’s arguments shortly.

Multiplicity of meanings of ‘normal development’:

We have seen in the examples presented various different uses and backgrounds of the term ‘normal development’, and analogous terms. We see two overwhelming types of ‘normal’, that which is a normal state or end-product of development, and that which is a normal course of development. It is clear that in both examples we can see a concern for how development should proceed, not the likelihood or frequency of it proceeding. There is language which is, on the surface, descriptive, but not far below the surface deeply normative.

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There are serious pitfalls which present themselves here – one is slippage from one meaning to another, the other is conflation. For the first, Fox Keller (2010) has identified the dangers of (mainly inadvertent) linguistic slippage in terminology in genetics. In the case of normal development, the slippage would be from a largely descriptive, frequency-based conception of normal development to a normative one. This move from describing what is frequent (under particular conditions) to what should be (under any conditions) risks leaving the supposed ‘normal’ outcome or ‘normal’ course as something to be expected rather than explained, with only the deviations to be explained. This epistemic asymmetry is neither acknowledged or justified, but it has been the subject of critiques by, among others, Oyama (2000). For the second, Moss (2003: 48-50) provides an example where different interpretations of the meaning and use of a particular term (in his case gene concepts) can be perfectly valid in and of themselves, but present difficulties when they are conflated. Again this applies to the normative and frequency or typicality based conceptions of normal development. I acknowledge that it is sometimes useful for terms to be fuzzy or flexible but at other times such confusion has been shown to be damaging and counter-productive (the examples given by Fox Keller, 2010, for instance).

Understanding normal development

Introductory section – two ways of understanding normal development

In this section I will present two ways of understanding the concept of normal development. I will argue that they are different, incompatible in one way, and yet capable of being integrated into a wider framework of understanding in another. These are the approaches of Love (2009) and Sober (1980).

Idealization

Love (2009) does not deal with developmental biology directly, but is concerned with the attribution of developmental stages to model organisms used in evolutionary developmental biology (Evo-Devo). He observes that “The study of ontogeny in model organisms is usually executed by establishing a set of normal stages for embryonic development… These normal stages are a form of idealization because they intentionally ignore kinds of variation in development, including variation associated with phenotypic plasticity” (Love, 2009: 679-680). Love identifies this idealization as a “reasoning strategy” (Love, 2009: 679) with a number of advantages, but some serious drawbacks as well. The advantages include a standardisation of stages which allows for the comparing, contrasting and replication of experiments and experimental results across different laboratories, and making it easier to draw generalisations across species (Love, 2009: 681). The weaknesses he identifies with this approach includes the aforementioned ignoring of variability due to phenotypic plasticity, but also the entrenchment of the disadvantages of prevalent model organismal practice as identified in the now classic Bolker (1995) paper (Love, 2009: 683). Such idealizations then “involving normal stages discourage experimental probing of phenotypic plasticity [which] … becomes effectively minimized, if not wholly effaced, from the study of ontogeny” (Love, 2009: 684). This is indeed a problem if, as seems increasingly the case, the processes that play a part in the developmental plasticity of the organism are more widespread than previously believed, and play a crucial role in development.

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Although he is primarily concerned with Evo-Devo, Love does speak enough about ontogeny in itself to be relevant to this discussion. Where his account differs in emphasis and orientation to mine is in his concern for the attribution of normal stages rather than normal courses, and in his focus on model organismal practice. While the first is a difference in emphasis that makes little difference to the validity of employing his arguments for my purposes, the latter is more problematic. In the examples I have given, not all were concerned with model organisms. In fact, excluding the textbook examples, few were to do with model organisms. This does perhaps undermine the extent to which the trade-offs which necessitate the attribution of normal stages for Love (and which he tries to suggest tweaks which work within these trade-offs) do not necessarily apply to many of the examples of normal development talk, which involve research in which the conscious decision has already been made to use non-model organisms.

Love’s account of idealization does present us with the possibility of the use of normal development as a regulative concept, an epistemic and methodological one based on the pragmatics and trade-offs of research. Here he differs from Sober’s account as I will outline below.

Natural and normal states

Why is it that the normal is so often conflated with the normative? One possible answer is in our conceptions of biology. Sober (1980) has formulated the Natural State Model which we can use as a guide here. Sober uses the concept of the Natural State Model in order to argue that evolutionary theory undercuts essentialist explanations for variation. He only touches briefly on the question of development, but I want to develop those thoughts more deeply and link what he does say on this and other aspects of the Natural State Model to the notion of normal development. Sober locates the origins of the Natural State Model in Aristotle’s scientific thinking. “Aristotle’s hypothesis was that there is a distinction between the natural state of a kind of object and those states which are not natural. These latter are produced by subjecting the object to an interfering force. …Variability within nature is thus to be accounted for as a deviation from what is natural” (Sober, 1980: 360). Sober identifies the value of such a model in providing a guide to the investigator to identify that, if it has not achieved the natural state, it must have been acted on by an interfering force, and that force can then be searched for and identified.

We can see that the natural in the natural state model is used in exactly the same way as the examples I have provided of the use of ‘normal development’. We can therefore see an equivalence, in Sober’s scheme, of the normal and the natural. This is a matter problematic by itself, as what is presumed to be normal is sometimes precisely not natural. There are ample examples of this normal unnatural slipping to become, in the thinking, practice and exposition of scientists, the normal natural. The example of the heavily constructed and artificial wild type is one such instance. Indeed, in order for experimental work under tightly controlled laboratory conditions to have any importance at all, an assumption must be made, implicitly or explicitly, that what goes on in the laboratory is a reliable indication of what goes on under more natural conditions, albeit with much of the confounding teeming complexity of changing interacting variables ‘simplified’ or standardised away. This is at the heart of what Garland Allen has termed the ‘experimentalist-naturalist dichotomy’ of two different ways of conducting scientific investigation (Allen, 1979).

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Such a way of thinking can be used to productive effect in sciences where the deviations from the natural state need to be discovered for three reasons – 1. To identify potentially harmful ‘interfering forces’ which can then be avoided. Examples of this could include teratology, identifying which factors embryos are exposed to can lead to what used to be described as ‘monstrous births’ (e.g. Gilbert, 2010: 28) and ecotoxicology, identifying what chemicals and combinations of chemicals lead to the death or reduced reproductive capability of organisms in the wild. 2. To identify potentially beneficial ‘interfering forces’, perhaps ones that organisms would not ordinarily be exposed to in natural conditions, but may improve (for human purposes) some aspect or characteristic of the organism. Agricultural research to boost yields or the nutritional value of organisms destined for human consumption is an example here. And finally, 3. To gain a handle on a mechanism of interest. An example of this would be exposure of DNA to X-rays to induce mutations to alter the sequence of DNA, with a view to identifying what role that particular section of DNA or gene plays in a particular process.

There is no doubt that such a Natural State Model is a way of thinking, a regulative concept in Kant’s meaning of the term, that can be very useful for scientific investigation, particularly that with a view to practical application. When it comes to act as a representation, it can be seen as an instantiation of the epistemic virtues of ‘truth-to-nature’ (Daston and Galison, 2010). However, it sneaks in a very big assumption, that of a certain type of teleology which posits not just a generalised tendency for the organism to be organised and purposeful towards the goal of the creation and maintenance of a living, functioning organism, but an organism with a pre-defined end point towards which it would, but for interferences, reach. And of course, it would have a set developmental course or trajectory along which it must travel in order to reach this end-point.

So what does Sober have to say about development specifically? “According to the Natural State Model, there is one path of foetal development which counts as the realization of the organism’s natural state, while other developmental results are consequences of unnatural interferences” (Sober, 1980: 374). But of course the organism has to live in an environment. According to Sober, “The Natural State Model presupposes that there is some phenotype which is the natural one which is independent of a choice of environment. The Natural State Model presupposes that there is some environment which is the natural environment for the genotype to be in” (ibid). So not only must there be a natural end state, this natural state must exist in a normal environment. One might even say in a natural environmental state. Sober does slip very quickly from talking about the development of individuals to the relationship between genotype and phenotype, and norms of reaction, which are concepts related to populations, not individuals. But while the discussion veers off individuals to populations, the point he has raised is very pertinent – if there is a natural state for an organism, there surely must be a natural environment, which doesn’t at any point function as an interfering force. The problem he identifies is exactly how to determine what that natural environment might be.

I will add another couple of issues to this. The first is the idea of niche construction – that to a significant degree organisms are not just passively exposed to the environment and its vicissitudes, beneficial or deleterious, but that they are actively involved in the construction of it. This insight feeds into a lot of the new developmentalist thinking over the past couple of decades, in the notion that the developing organism is at least partly responsible for its developmental environment and

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therefore for the developmentally-relevant inputs, information, resources it obtains from that environment.

Another issue is that intervention, restriction and challenge from the environment, however seemingly interfering a force, can actually have a crucial part to play in what we might call normal development, if we see normal development as the attainment of a typical, desired, set end state. The development of bones is a classic example here, requiring resistance and stress in order to develop properly, but the presence of gut bacteria has been shown to be essential for proper development of the mammalian gut (Gilbert and Epel, 2009: 101).

The third is that while various environmental inputs may take development in different directions, the fact that there are multiple possible functional end-products of developmental processes means that there is (at least not always) no privileged desired end-state towards which development tends if not blown off this royal road. Furthermore, though one or more of these developmental pathways (if the end-states are largely discrete in character, though many will be continuous) may be more common, each and every end-state needs to be explained in terms of the developmental processes and mechanisms that resulted in it. There can be explanations sought and offered as to why one end-state is more common than others even in identical environmental conditions (if this were attainable), but there must be explanatory symmetry between consideration of all the end-states.

It is worth noting here that Aristotle did not believe that the reaching of this end-point, presumably defined by the formal and final causes was actually possible, and that always some interfering forces would inevitably deflect the organism from the completely natural path. But there could be varying degrees of deviation. Tied to this particular type of teleology there is a presumption of explanatory asymmetry. The natural state is not something to be explained, but the non-natural state is. Once a pre-defined end state is invoked, reasons must be given why it has not reached it, and no reason would need to be provided as to why it did.

Conflict and resolution?

On the basis of the preceding sections, it would seem that there are two conflicting possible interpretations of normal development. One, Sober’s, is a deeper, metaphysical approach. The application of the notion of a natural state – or we might say a natural course – is deeply descriptively and normatively normal. When a scientist thinks in this way he considers normal development to be the paradigm case of development, and departures from this are to be explained, but the paradigm case need not be. Love’s idealization on the other hand is a less deep epistemic approach. Here the invocation of normal development need not betray any ontological or metaphysical commitments, but merely establishes a typical developmental state and course. The typical need not be understood as a paradigm case in the way that the normal development in the Natural State Model would be. The typical here is necessarily descriptive, but not normative. However, in the everyday practice of science, it is easy to see how the descriptive may bleed into the normative, for a scientist frustrated that their embryos are not doing what they are supposed to do, the normal state, stage or course being relied upon to get embryos to a particular expected point in which the scientist is interested in or at which they can intervene. We can see, once this elision has occurred, that the normal may become something of a soft paradigm, and a – more ramshackle – explanatory asymmetry established between the normal and the not-normal cases.

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Despite the fact that, on one level, the Natural State Model and Love’s idealization provide two very different ways of understanding normal development, we can see a way that they can be integrated. They are certainly not mutually exclusive is we assign each to a different ‘domain’ – Love’s Idealization to the methodological and epistemic and the Natural State Model to the metaphysical and ontological – and adopt perhaps an instrumental ignorance of the connections between those domains.

I submit that it is possible that normal development is a concept where once the basis of it was something approximating the Natural State Model outlined by Sober. This underpinned an idealization in Love’s sense. Now that the Natural State Model version of normal development is under increasing strain and criticism, it brings into question the epistemic superstructure. It is entirely possible that this ‘superstructure’ can survive the crumbling of its metaphorical foundations. It is not at all clear that this is desirable. The extent to which this process has occurred, is occurring and at what pace is not at all clear. It is an open question whether in developmental biology the Natural State Model and idealisation (in the sense that Love outlined) still persists, or whether what is left is just the idealisation identified by Love.

An alternative to the problem

Introductory section:

There are various kinds of normal development talk – typical course, typical state, normative course, normative state, gross processes, specific processes. I have identified the problems that this may cause, and also the problems with the concept of normal development given changes in the understanding of and approach to development.

Perhaps in the light of these problems, it would seem to make sense to abandon talk of normal development as riddled with an outmoded Natural State Model and teleological thinking, which does so much harm to our attempts to understand living organisms and the processes which generate them. If we are to have a concept of normal development, it should be shorn of final causes, teleology, goal-directedness and purposiveness. Normal development should be a concept that is free from this infection, and the infection of normativity, and solely concerned with being a useful term to use to denote typicality, expectedness and so on. Tempting yes, but with absolute freedom from infection comes sterility. It has been argued elsewhere that normative thinking and teleological thinking are not necessarily problematic for biology.

Shedding teleological thinking?

If one of the main problems that has been identified with ‘normal development’ talk is the assumption of a specified end-product of development, with normal development as the proper course towards reaching that end, and intermediate normal states as milestones towards that, surely this is a kind of teleological thinking that we can do without? I would agree, but only in the sense that it is this kind of teleological thinking we can do without. Regardless of whether it is named teleology, teleonomy or any other term you care to coin, biologists and philosophers have recognised the utility of teleological thinking as a regulative concept guiding scientific thinking and research. If the biology has shown that the teleology of the specified specific end is untenable, I

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propose that a different teleology, based on the end of maintaining a living functioning organism, possibly one capable of reproduction. This is a much broader teleology, but it is one which at least is compatible with, and indeed foregrounds, plasticity, robustness and all the developmental processes which work towards this goal. Indeed, it would not perhaps be an outrageous step to suggest that this conception of a developmental teleology may in fact be constitutive as well as regulative. These are certainly the steps that would be taken by Walsh (2012), who identifies not just that “Goal-directed behaviour is a gross property of the system as a whole” (Walsh, 2012: 177), allowing for a teleology that can be conceived as a broad end which could mean a general maximisation of the level of functional performance (after Amundsen) of the organism as a whole, but that “goal-directed systems” tend to “exhibit three kinds of properties: persistence, plasticity…, and … repertoire” (ibid). The first two were dealt with in the discussions on robustness and plasticity, repertoire on the other hand is simply that “the system has the capacity to produce an array of responses to occurrent conditions” (ibid). We could perhaps say that as well as those three comprising properties of goal-directed systems, we might be able to identify goal-directed systems from the presence of at least the first two properties.

Shedding normativity?

If we are not to ditch teleological thinking about development, what of normative thinking?

There are many philosophers who would argue against such a move. For instance, there is Barham’s (2012) persuasive argument that we must accept the existence of normativity (and agency) in the operations of all living organisms. Christensen (2012: 112) demonstrates that “without an account of valuational normativity we are left with an incomplete understanding of key phenomena like regulation and adaptive plasticity.” While certain types of normativity are then undermined by our understanding of developmental plasticity, we cannot fully understand this plasticity without some type of normativity. On this basis it would then be unreasonable for the scientist to ignore the normativity of development in their own discussions about organisms or indeed discard a normative conception of normal development. One of the major problems identified with the usage of normal development was not that it was normative, but that the descriptive sense of normal was either bleeding into or being conflated with normative senses. We should also recognise that just as there is more than one way of being normal, there is more than one way of being normative.

If normativity is to be retained within developmental biology and any reformed concept of normal development, it would certainly need to be a radically pared down type of normativity to the rampant version currently present. Such a new sense would involve a teleology based not on specific structures and functions, but on a generalised end of a functional, surviving (and possibly, desirably, reproducing) organism, with at least a minimal level of function. Here the exact functions are unimportant, in Amundsen's terms (2000), the mode is irrelevant here, but the level is relevant. If the end is such, a degree of remaining normativity is tolerable, and does not do any ontological or metaphysical work beyond what can be accepted within the framework of a science which is concerned ultimately with the development and sustenance of a functioning whole organism. This is the case even if the development of specific functions or structures of interest is the scientific project. The fact that the particular phenomenon of interest is not the whole organism does not

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mean that the development and maintenance of the survival and persistence of the whole organism is irrelevant - it is simply backgrounded on a pragmatic basis.

States and processes

My argument is that the problem with the concept of normal development as applied by scientists yesterday and today is not that it is imbued with normative or teleological thinking, but that a concept of normal development solely relating to the expected end-point of a narrow path or course of development understood in a certain teleological way of thinking is at the heart of the problem with normal development.

This leads to the warping of perspective towards an interest in deviation from the form, from the expected end-state, rather than an interest in how a particular end-state was generated, by looking at how dynamically it developed. Some of the major new innovations in developmental biology concern how developmental processes operate not just to construct the organism, but how they incorporate resources and adapt, adjust, tweak their operations to ensure that the organism not only sustains but thrives in the best manner possible given the circumstances. Living organisms not in the laboratory do not live in carefully controlled, standardised experimental conditions, nor are they standardised or carefully controlled themselves. They live in a world teeming with problems, insults, opportunities, varying climactic, kinetic, nutritional, socio-cultural contexts through which they move during their ongoing development. A growing interest in developmental biology on robustness and plasticity – how organisms sustain and change, by coping with changes in conditions and occurrences in development itself as well as changing to meet those circumstances and ensure that the organism is able to cope and thrive – means that this growing interest in process and processes must be matched by a reframing of the concept of normal development in terms of process rather than state or set course. To do this counterposes not abnormal development to normal development but pathology. Earlier I quoted Canguilhem’s definition of pathology as counterposing normality in the sense that the pathological individual is unable to interact with its milieu in a way that it can co-construct the milieu and itself in order to maintain itself and thrive. In this way, Canguilhem’s conception of the normal and pathological, as processual interactions rather than states or set courses, is perhaps a more fruitful way to think about development. It is perhaps worth pointing out here that Gilbert and Epel (2009), who spoke of normal development being altered as well as developmental trajectories by factors in development, barely use the word abnormal even if they do employ the terms normal and pathological. We can therefore be normative about developmental processes and the relation of the developing organism to its milieu, even if normativity about states and courses of development are ruled out.

We can think of development in this way as continual revision and alteration of the final cause, and the formal cause of the organism, both located in the developmental processes and the resources that they see fit to employ. If the processes are operating (or indeed, allowed to operate) to the end of the highest functional level of performance possible given the environment in which the organism lives and with which it interacts, this is normal development. If they are not, this is pathological. Using these words in this initially explicit way will aid thinking more easily along the lines it is already development, and avoid slipping back into modes of thought that have been rejected as leading to dead ends. I do not intend to suggest a linguistic determinism, or a completely constructivist

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approach to scientific changes, rather I think that there are ways that it is easier for science to be realist and correct, and ways that are harder. Even if the particular perspective one has is opposed to mine regarding my thinking about development, I hope I have shone a light in which other implicit assumptions, perspectives and modes of thinking can be sneaked into seemingly innocent phrases and guide thinking away from the direction the thinker wants to head in.

Further issues and implications

There are some issues which I have been unable to pursue here, partly for reasons of space, partly because I have not worked out all the aspects of the problems.

I have touched upon, in my discussion on ‘understanding normal development’, the relations between the metaphysical and ontological commitments possessed by scientists and their epistemic approach to living organisms and processes, but I still wonder how such an exploration might be deepened, perhaps using the concept of normal development. This is something which could feed into my work on preformation, epigenesis and biological enquiry into development around the turn of the last century. The relation of concepts of normal development to the norm of reaction is another possibility for further work, here I have been inspired by a hint in McLaughlin (2003: 68).

Indeed, I would like to pursue further the implications and uses of the analysis I have conducted on normal development to help inform our understanding of the concepts of preformation and epigenesis, and explore in greater depth the relationship of different kinds of teleological thinking to conceptions of normal development. Hopwood has provided some openings through which I might apply a finalised analysis of normal development back to the period that most concerns me in his work on Wilhelm His (Hopwood, 2000) and on normal stages (2005, 2007). There are also tantalising hints of Roux’s discussions of normal developmental processes (see, for instance, the mention in Pauly, 1987: 49), and Ribbert’s concern for how “deviation from normal processes” might occur in development and growth (Moss, 2003: 128).

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