The Epigenetic System and The

The Epigenetic System and The

The Epigenetic System and the

Development of Cognitive

Functions

JEAN PIAGET

1 Preformation and Epigenesis

The problem that has always arisen before one could tackle ontogenesis has been preformation or epigenesis. With the usual veering of fashion in the history of ideas, the tendency of many writers today is to return to the more or less strict preformation standpoint. Their grounds for this are that the chain or helical structure of the DNA or deoxyribonucleic acid molecule is susceptible of a combinatorial arrangement of its elements where "combinatorial" covers, by definition, the set of all possibilities. But if it is difficult, from the phylogenetic point of view, to conceive of man as preformed in bacterium or virus, it is every bit as hard to make out how, from the ontogenetic point of view, the main stages of "determination" or induction, and, most important, of the final functional "reintegration" of differentiated organs, could already be present in the initial stages of segmentation. Furthermore, Waddington has stated categorically that the idea of an entirely predetermined system in the DNA, however fashionable it may be at the moment, is just unacceptable in embryologya. At the symposium on this subject at Geneva in 1964, in the course of discussion about the regulations of development, he made a very profound comparison between epigenetic construction and a progression of geometric theorems in which each is rendered indispensable by the sum of those preceding it, though none is directly derived from the axioms underlying the original one.

See Waddington (1975) — cited under Further reading. (Editor's note.)

"The Epige'netic System and the Development of Cognitive Functions" is an excerpt from: Jean Piaget, Biology and Knowledge (Edinburgh University Press and University of Chicago Press, 1971, section 2, pp. 14-23) and is reprinted by kind permission.

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The comparison of epigenesis with a progressive mathematical construction comes home to us all the more forcibly because the growth of elementary logico-mathematical operations during the ontogenesis of intelligence in a child raises the same problem of preformation or epigenetic construction as that which forms the basis of discussion about causal embryology.

We shall, indeed, find ourselves compelled to trace the origin of logico-mathematical operations back to an abstraction made from the general coordination of actions. On the one hand, such operations cannot possibly be based on the objects themselves, since abstraction from objects can give rise only to non-necessitous statements (in the sense of deductive necessity) or, to put it more precisely, to judgements which are merely probable, whereas it is characteristic of logico-mathematical operations that they have an internal necessity attributable to their complete reversibility (and therefore not physical): for example, if i= a/ — 1, then i x i = — 1. On the other hand, reunion, order, and interchangeable schemata are to be found in the general coordination of action, and these constitute the practical equivalent and even the motor equivalent of future interiorized operations.

If these elementary logico-mathematical operations are based on the coordination of actions, by means of reflective abstraction drawn from sensorimotor schemata, do we have to conclude that the whole of mathematics is laid down in advance to our nervous system? Not only is this unthinkable, but the facts prove that logic itself, even in its most "natural" forms, is by no means innate in human beings in the sense that it exists at any age. Even the transitivity of equals or of cumulative differences (A = C if A = B and B = C, or A < C if A < B and B < C) is by no means obvious to a child of four to six years when he has to make a comparison between lengths and weights on first perceiving A and B simultaneously, next B and C, but not A and C (A subsequently being hidden and so presenting the problem).

The task of finding out about this transitivity raises all the main problems of epigenesis. Is this transitivity inherent in the genotype of the human species? If so, why does it not automatically come into play at about seven or eight years (and about nine or ten for weights)? Because, it will be said, new conditions are indispensable if the inherent virtual is later to become actual: for example, the intervention of regulatory genes or the collaboration of a number of genes not so far synergic (by reference to genetic or genie coadaptation, to use the currently accepted term). However, as these differentiated regulations are not made at any definite age in the particular case but may be accelerated or retarded according to conditions of exercise or acquired experience, they certainly exercise factors which are indirectly connected with environment.

Can it then be said that transitivity is utterly unconnected with the actions of the genome and solely dependent on phenotypic actions of the organism in relation to environment? In that case, how can it become "necessary" and generalizable? Because those actions which exert an influence on environment

b Piaget defines "reflective abstraction" as the process of "reconstruction with new combinations, which allows for any operational structure at any previous stage or level to be integrated into a richer structure at a higher level" (section 20, part 4, p. 320 of Biology and Knowledge). (Editor's note.)

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are influenced in their turn by the more generalized forms of internal coordinations of action? If that were so, would then generalized coordinations depend, in their turn, on the most common and deep-seated coordinations of the nervous system, which brings us back to the genome?

The evidence thus proves that the problem of preformation or epigenesis has nothing about it that appertains specially to organic embryogenesis, and it crops up in its most acute form every time we discuss the ontogenesis of cognitive functions. It may be objected that the problem is settled in advance, since the various aspects of intellectual behavior are phenotypic reactions and a phenotype is the result of interaction between the genotype and the environment. That is indisputable, but one still needs to explain in detail how, in the field of knowledge as in that of organic epigenesis, this collaboration between the genome and the environment actually works - especially those details which concern autoregula-tions or progressive equilibrations which admit of the exclusion of both prefor-mism and the notion of a reaction caused entirely by environment.

2 The Sequential Character of Stages

In this attempt at elucidation, the first step forward should be an examination of the sequential character of development. We call sequential a series of stages, each one of which is a necessary part of the whole and a necessary result of all the stages that precede it (except for the first one), as well as naturally leading on to the next stage (except for the last one). This seems to be the case with the embryogenesis of Metazoa, since the main stages constantly repeat themselves in the same order. However, no experiments have yet been done to control the impossibility of doing away with one stage, though these will doubtless be performed some day if someone succeeds in isolating processes which entail considerable speeding up or slowing down of the succession of stages. A further argument in favor of the sequential character and generality of the stages is the fact that, in mosaic-type embryos, namely at the initial level studied, those which have shown incomplete regeneration when separated from a blastomere reach a stage of partial control if the seed is split at the virgin egg stage (Ascidies de Dalcq).

Now this same problem about the sequential character of stages appears again in psychology in connection with the development of the cognitive functions. It is important to note that in this sphere the stages became increasingly clear and sequential in relation to controls that are better differentiated and of wider application.

Psychologists have relied too much on the notion of stage. Some speak as though it were nothing but a series of actions, not always, though "generally," in a constant order, and supposedly sharing a dominant characteristic, nothing more - which opens the door to arbitrary thinking. This is what Freud means by stages, for example, as far as the affective is concerned.

When it comes to intelligence, however, we use the term stage where the following conditions are fulfilled: first, where the series of actions is constant, independently of such speeding up or slowing down as may modify the middle range of chronological age1 in terms of acquired experience and social environment (like individual aptitude); second, where each stage is determined not

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merely by a dominant property but by a whole structure which characterizes all further actions that belong to this stage; third, where these structures offer a process of integration such that each one is prepared by the preceding one and integrated into the one that follows. For example, without going into great detail about particular stages, three main periods can be seen in the case of operative intelligence:

A.A sensorimotor period (from birth up to one and one-half to two years)
during which sensorimotor schemata ranging up to acts of practical intelligence
by means of immediate comprehension (using a stick or a piece of string, etc.)
are established as well as practical substructures of future notions (permanent
object schema, spatial deplacement "group," sensorimotor causality, etc.).

B.A period that begins when the semiotic function (language, game symbols,
picture making) manifests itself and goes through the preparatory phase of
preoperative representation (nonconservation, etc.). This ends not later than the
eighth or ninth year with the setting up of operations which are called "concrete"
because they still have a bearing on objects (classifying things, putting them in
series, noting connections, understanding numbers).

C.A period beginning at about the age of eleven or twelve which is charac
terized by propositional operations (implications, etc.) with their combinatorial
quality and their possible transformations made by relation to a quaternary group
— a combination of two elementary reversibility forms (inversion or negation and
reciprocity).

A stage system of this kind (stages which can actually be even further differentiated into substages) makes up a sequential process: it is not possible to arrive at "concrete" operations without undergoing some sensorimotor preparation (which explains why, for example, blind people, having badly coordinated action schemata, may be retarded). It is also impossible to progress to propositional operations without support from previous concrete operations, etc. Thus, one is confronted with an epigenetic system whose stages may be characterized by fairly precise structures: coordination of sensorimotor schemata reaching certain invariables and an approximate reversibility (though in successive actions); "groupings" of concrete operations, that is, those elementary structures which are common to classifications and serializations, etc.; and combinatorial with a quaternary group at the third degree.2

By contrast, in the field of primary perceptions (or field effects) no comparable system of stages is to be found, and, as to behavior of medium complexity (perceptive activity in exploration, etc., and mental images), an intermediary situation is found halfway between an absence of stages and stages limited by their progressive integrations. Thus, everything seems to happen as though the more complex - in their organization and autoregulation systems - cognitive systems are, the more their formation is dependent on a sequential process comparable to a biological epigenesis.

3 Chreods

If a detailed study is to be made, that is, if the evolution of broad concepts or of particular operative structures is to be studied separately, then each one may

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give rise to its own respective stages in the midst of which is to be found the same sequential process. But the interesting thing about this point is that it presents us with differentiated channels, each one of which is nevertheless relatively even and follows its own course while still giving proof of varied interactions with the rest.

Waddington has suggested the name "chreods" (necessary routes) to describe developments particular to an organ or a part of an embryo, and he applies the term epigenetic system (or, epigenetic "scene") to the sum of the chreods, taken as being - to a greater or a lesser degree - channeled0. But the main interest of this idea is not just in the names he gives things (or in the symbolic patterns thereby presented to us, of channels, some wide, some narrow, that the processes must follow). It is, rather, in a new concept of equilibrium as something which is, as it were, kinematic and which, in determining such processes, is nevertheless quite distinct from homeostasis: there is a kind of "homeorhesis" when the formatory process, deviating from its course under outside influence, is brought back on course by the interplay of coercive compensations. In Waddington's opinion, such a mechanism is dependent upon a network of interactions rather than upon the action of individual genes; each group of genes is not even homeorhetic, and its return to a moral course or chreod presupposes, in this way, a complex interplay of regulations. It is true that some influence systematically exerted by the environment may eventually lead to lasting deviations in the chreod and to the consolidation of a new homeorhesis, but this is not the moment to raise such a problem. On the contrary, we would do better to emphasize the fact that the chreod and its homeorhesis do have a space-time aspect, not merely a space one. Differentiation in chreods is regulated in both time and space. The various channelings as well as the autocorrections which assure their homeorhetical equilibrium are under the control of a "time tally," which might well be described as a speed control for the processes of assimilation and organization. It is, then, only at the completion of development or at the completion of each structural achievement that homeorhesis gives place to homeostasis or functional equilibrium. In the latter case, the question naturally arises of determining the relationship between the two.

It is impossible to take note of such a picture without immediately thinking of the far-reaching analogies it has with the development of schemata or ideas in the intelligence, and with that of operational structures.

To put the matter in a familiar way, let us begin by noting that these analogies are very far from being universally accepted; very rarely have I been able, in America, to expound any aspect of my stage theory without being asked, "How can you speed up this development?" And that excellent psychologist, J. Bruner, has gone so far as to state that you can teach anything to any child at any age if only you set about it the right way. My answer to this is in the form of two questions: first, would it ever be possible to make the theory of relativity or even the simple handling of propositional or hypothetico-deductive operations comprehensible to a four-year-old? And, second, why does a human baby not discover the continued presence of something that he sees you hide beneath a screen until he reaches the age of nine months and upward, whereas kittens (in a study made

c See Editors note a.

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by H. Gruber when he discovered the same preliminary stages in them as in us) do so at three months, even though they make no further progress in coordinating successive positions?

The truth, it seems to me, is that every notional or operational construction implies some optimum length of time, the expression of the most favorable transformation or assimilation speeds. This is because such a construction contains a certain number of necessary stages whose itinerary is the equivalent of a "chreod." In the sphere of the mind, where social influences are added to factors of physical experience (material environment), deviations easily occur, and short circuits too. Thus, the natural way for the mind to attain the concept of whole numbers consists of syntheses of inclusion of classes and the sequence of transitive asymmetrical relationships, in spite of the fact that the latter two systems develop along partly independent lines. Now the natural structure of the number concept can be modified in various ways. First of all, as is done by many parents, it can be taught the child verbally - ten to twenty, etc. But this only modifies the child's comprehension very slightly; we are constantly coming across subjects of four to five years old who will deny the equality of two piles of objects, even though they have counted what is in each pile as being perhaps seven or ten, because the way the objects were arranged in space or subdivided into small groups was changed each time. In such cases, outside influences, such as counting out loud, only produce a slight deviation leading back to the "chreod" at the four- to five-year-old level, for lack of any means of assimilation at higher levels. In other cases, a genuine acceleration can be set up, but only at one point (for example, in experiments where transfers are made one at a time in succession, thus facilitating, by repetition of the same actions, the synthesis of inclusions and the serial order).3 This local synthesis is not necessarily followed by comprehension, nor will it guarantee retention of the number in transfer experiments between groups of objects arranged differently on different planes.

Briefly, intellectual growth contains its own rhythm and its "chreods" just as physical growth does. This is not, of course, to say that the best teaching methods, by which we mean the most "active" ones, cannot, to a certain extent, speed up the critical ages dealt with so far, but this speeding up cannot be indefinitely continued.

4 Maturation and Environment

The epigenesis of the cognitive functions, like any other, does, in fact, presuppose an increasingly close collaboration between the factors of environment and the genome, the former increasing in importance the larger the subject grows.

The factors relative to the genome are certainly not to be left out of account, in spite of what some scholars, empirically oriented, have said about all knowledge being drawn from outside experience. At this stage of our knowledge, these factors certainly cannot be tested in detail, but the best indication that they do intervene is the fact that the maturation of the nervous system is continuous right up to the age of fifteen or sixteen years. This, of course, in no way implies that ready-made knowledge is written into the nervous system from the outset in the way that "innate ideas" are, and, even if this idea proves acceptable in