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3. EMBRYOGENESIS AND COGNITION

3.1 Chemical communication between cells. Motion and morphogenesis.

It is easy to understand the network of bio-oscillatiors when we concentrate on a relatively simple model. We introduce a chemical oscillator that drives a change of behaviour and, later,a change of form, during the life cycle of the cellular slime mould: Dictyostelium discoideum. This useful Amoeba lives in our soil, and has been extensively studied by Bonner (1993) and recently by A.F.M.Marée (2001) who produced  animations of their morphogenesis (Stan Marée, 2001). An amoeba colony develops from a few thousand separately living, vegetatively reproducing cells. When one of the individual cells has reached a phase of maturity, it starts to produce cyclic AMP. It is a relatively simple metabolite, and it signals to other cells to produce and release more of the same substance. Moreover it appeals to the cells to move in the direction of the source of the chemical signal, thus causing aggregation of cells. When a certain level of AMP has been reached the cells start to produce phospho-diesterase, an enzyme that destroys cyclic AMP. By its presence the signal of the newly formed AMP is rapidly turned off again. A prey-predator type of oscillation ensues. The release of the signal substance spreads as a pulse-wave in concentrical circles over the population and causes the cells to move in shifts towards the centre where the substance was first released. In this way colonies of cells are called together around a 'pacemaker' cell (aggregation). Where the waves meet those of other pacemaker centres the colonies compete with their neighbours for allegiance of uncommitted amoeba in this no man's land.

In a second phase the now compact mass of cells moves over the surface in a manner that resembles a crawling creature; it is in fact called a slug. The motion is periodic and has about the same frequency as that of the pulsing wave motion of aggregation that was observed in the first phase. One sees peristaltic waves of contraction travelling antero-posteriorly. The same metabolic substance, cyclic AMP, that in conjunction with chemotactic response, has caused a spatially organized aggregation field, now generates movement in what has become a multicellular individual.

Two antagonistic chemicals alternate in oscillatory fashion. In synergy they produce a new behaviour, a new form, a development towards a more complex strategy for survival. That becomes evident in a third phase. The same chemical oscillatory signal causes a further differentiation of parts of the colony. It establishes a morphogenetic field first in one large partition, then in successively smaller divisions that grow out into stalks. The stalks finally lead to the development of fruiting bodies and spore cells. All this happens by alternating messages: chemical message (1) says: follow the scent; chemical message (2) says delete the scent-trail. The signal spreads in the form of waves . Depending on the phase in which the waves approach each other a behaviour emerges: the colony moves by projecting pseudopodes, or the mass of cells forms stalks or limbs. There is a continuity of development and behaviour: the spreading of a metabolic process, in the form of pulse-like waves over an excitable medium, becomes manifest in one context as morphogenesis and in another as motion.

Growing form can be distinguished from function and behaviour, by a difference in pacemaker frequency and wave propagation velocity. 'Embryonic pacemakers characterised by slow periods of oscillation are sculptors of form, while for instance neural pacemakers having periods of fractions of a second are too fast for mass cell movements, and result in patterned activities rather than patterned forms' (Goodwin 1976).

Thus it appears that the difference between emerging body-forms and body-functions is their position on the time-scale. More than one philosopher will be surprised that the eternal question of the relation between matter and mind, form and function, has a simple answer. Because function has the shorter response time, it can induce change in form. And, because form has the longer response time, it can determine function. Form and Function are allies in a two-way hierarchic relationship to each other.

Form and function develop according to the same principles and lie at opposite ends of a time-window

Chemical communication shows its linguistic structure.

B.J.Eshel and colleagues (2004) explain that colonies of bacteria have developed intricate capabilities for information exchange between individual cells and between colonies. Cells use chemotactic signals, they can sense when a colony has reached a critical mass to start spore-production, they communicate by exchanging plasmids. By cooperating they self-organize into highly structured colonies that adapt intelligently to new environments.
Because the genome and the intracellular signal transduction are flexible, the quasi-organism forms into an adaptive network. The authors propose this to have a linguistic structure:
the shared interpretations of chemical cues follow rules of grammar
the exchange of meaningful chemical messages is the semantic content, 
the probing dialogues with the environment are the equivalent of pragmatics.
Meaningful communication is based on colonial identity. It allows intentional behaviour (e.g. pheromone guided courtship before mating) and purposeful revision of colony structure (e.g. for the formation of fruiting bodies). Recognizing and identifying other colonies might be considered a form of social intelligence

3.2 Resonance in a morphogenetic field. Dancing to the chemical beat.

Other substances such as serotonin and acetylcholine have also been shown to create morphogenetic fields during embryogenesis. We'll discuss one more case of differentiation under the influence of a chemical substance. It illustrates the variable effect of chemical oscillations that act first on one partition or 'resonating space', and in following stages find that the resonating space has split up in parts, so that the oscillation produces 'partials'. I summarize a description by S. A. Newman and H. L. Frisch (1984) on the embryonic formation of limbs.

The limbs of vertebrate species show special adaptations. There are limbs for walking, elongated limbs for swinging through trees, fins and flippers for swimming and paddling, wings for gliding and flapping. Different though they may be, they are variations upon a common theme. Extending outward from the body, an increasing number of bones are found within a sheath of skin. The human arm has one humerus, two bones in the forearm (the radius and ulna), two rows of four in each wrist and five jointed chains of bones for each hand. The leg and foot show an analogous arrangement; so do the body-parts in other species that are used for motion.

The phenomenon of distal multiplication is explained by a peculiar 'dance of the cells' that is executed during morphogenesis of those limbs. In the mesenchyme (the primary substance of the beginning limb bud) some cells close to the body wall are transformed into cartilage: they aggregate and form tight clusters. Neighbouring cells follow, and together they change from individual cells, spread out over a given space, into a close-knit tissue of cartilage cells in the middle of the space where later the bone will form. They aggregate under the influence of a chemical signal, fibronectin, that is distributed unevenly in the mesenchymal area. , The agglomeration and subsequent changing of the cells occurs where its concentration is highest It is this concentration of cells that is dancing to the music of resonating chemical waves. In a closed space, where wave propagation is thrown back on itself, there will be a standing wave pattern, with nodes where the concentration of the proteïn is highest. Resonance will take place in a fundamental tone mode (no harmonics) or in an oscillating-mode with one or two harmonics (that is: peaks and valleys in the concentrations of fibronectin), when the resonating space becomes smaller. As the limb formation progresses, the the partition keeps narrowing: the number of nodes will multiply, and so will the number of bones. In the view of these authors the differentiation of parts of vertebral limbs (time window of epigenesis) is analogous to the production of overtones in a flute or a violin (time window of audio-frequencies).

3.3 Chemical oscillators in different contexts.

The very same substances that have been involved in the timing of embryonic development, will later in life fulfil roles that appear to be entirely different. We have seen that cyclic AMP has a career as a director of [1] aggregation, [2] movement and [3] differentiation, depending on the phase of the developmental cycle, and the context in which AMP is the messenger substance between communicating cells. In the adult vertebrate organism the same AMP plays a role in brain metabolism and behaviour development.

The developmental fields created by metabolic activities in the embryo, can be compared with the fields that shape behaviour and cognition in the developing and learning brain. Such fields control the growth and function of neural structures which define a context and a meaning for perceptual and behavioural events (Goodwin 1976).

The analogy between developmental fields in the embryo (in the time-window of epigenesis) and those in developing cognition (in the time-window of attentional integration during learning) will be taken up again in Chapter 7. When looking at the competing cell-groups in an embryo, that derive from three different types of germ-tissue we will be impressed. We will discover that the outcome of the competition has far reaching consequences for a person's later behavioural style, his way of life and even the value system by which he assesses his environment.

The variation between human individuals is due to hereditary factors interacting with influences from the environment during epigenesis. Think of the limb-formation with its ever smaller compartments. Similar to the phalanges of the fingers and toes that acquire their finishing touches by vascular and nerve-supply, other final developments occur everywhere in the organism. Usually the highest resonating overtones are still in harmony with the driving fundamental oscillation. Local influences however can bring about unwanted variations, such as syndactylism (joined fingers or toes) cleft palate or congenital heart defect. Similarly unwanted variations in the finishing stage occur in neuroanatomical structures and neuropsychological functions. The relation between growth, maturation and learning will be discussed in Chapter 8. By studying that map, such developmental disorders as dyslexia, cluttering and stuttering can be better understood.

3.4 The energetic aspect of information: absent in R.Sheldrake's concept.

R.Sheldrake speaks of morphogenetic fields and motoric fields as having no material or energetic substance, and as exerting their influence regardless of distance. This is attractive to those who like magical thinking: they recognise a supporter of their belief. That may be a reason that his view has received a certain popularity, although there has as yet been no experimental support. Sheldrake's fields lack the essence of Goodwin's fields: a physical and chemical empirical reality. As discussed here, morphogenetic fields show gradients of active chemicals, in periodic pulsation. More important, these oscillations interact with other chemical oscillators. There is kinetic energy involved in the information exchange. Just as in a tone produced by a flute or a violin, the amount of energy is small. However no sound or signal can be produced without energy.

Do thoughts have an immaterial existence? Those who disconnect mind-power from the material world will answer affirmatively. For instance, because we can 'think' a tone without actually producing one, that tone is deemed to have an immaterial existence. Likewise, according to magical reasoning, all living things have some immaterial representation in the world, by which they can become morphogenetically active. This is, I think, an erroneous conclusion. Even the human thinking process requires energy supplied by a material process. There is no reason to believe that the Master of the Universe thinks without using energy. Why would he, he is all energy and information.

We have compared the complex chords, caused by many coupled oscillators in a developing organism, to sounds of music. Although there is a score, there is also room for free musical interpretation and even improvisation on the spur of challenges from the external world. If one thinks that the 'score' for a developing individual has an immaterial existence, one overlooks the fact that the relevant information in the score has to be 'read' by the substrate upon which it acts. For writing and reading of codes a minimum of energy is needed. Even quantum theory provides no escape. Therefore, it makes no sense to describe the musical score as an immaterial concept: a correction in the score cannot change a performance without intervening energy. Bringing about a correction in the score, changing the code, also demands the mobilisation of energy. In an exchange of information only a minute amount of energy is used. To some this amount may seem negligible, but it is on the contrary essential.

The exchange of minute amounts of energy during the transmission and reception of signals has consequences for our ideas about motivation and mind-power. Motivation for all activities in life such as growing, moving, fleeing or fighting, has its primary source in the genome. Primary drives differentiate into successive layers of secondary and tertiary motives, that meet environmental demands. Finer differentiation and more adjustment occur in the outer layers or shells that are most closely in contact with the environment. This concentrical model, which will be more closely discussed in Chapter 5, enables us to see morphogenesis and behavioural motivation as processes lying on a continuum. Most students need a large amount of mental practice before they can grasp the concept of mind and body being one. The following pages offer material for this practice.

3.5 Freedom and determination on the level of cells.

In embryogenesis a cell on its way to differentiation of function, may 'change it's mind' up to a certain point in its development. This happens for instance when, by migration, a cell arrives into another morphogenetic field than the one it grew up in. Since field organizers operate in progressively smaller partitions, cells at the boundaries of these domains will often be required to change their developmental pathways, because at the transitions it is uncertain to which domain a cell belongs. The initial field covering the whole embryo becomes partitioned into subfields corresponding to head, limbs etc. Then finer partitions arise within these domains generating vision-fields, olfactory fields etc. Reallocation of cells to make up for deficient fields in a damaged area is an instance of regenerative power.

Cells are continually tested whether the developmental pathway they follow is the correct one. Variations during genetic unfolding are compared with the exigencies of the immediate environment, that is the neighbouring cells which determine the morphogenetic field. Positive selection means that the developmental direction is reinforced. In the case of refusal the cell may move on until it finds a more reinforcing environment, or it may switch the direction of its developmental pathway, or it may do both. We have seen Darwinian evolution in action in the time-scale of cellular replication.

3.6 The organism as a cognitive system.

The behaviour of a particular cell is meaningful in the context of the field it finds itself in. Lens formation is useful only within the context of the eye. When a cell has finally differentiated into a transparent fibre as part of the refracting body of the lens, it can be said to have generated a useful representation of a property of light: by refraction it projects a part of the perceived world on sensory receptors. This property has found a meaningful representation in the developing organism. Such a useful representation of a relevant part of the environment in an organic form and in an appropriate function can be called knowledge (Goodwin 1976). Organisms are cognitive systems that have collected their knowledge in the course of evolution. In other words: cognition is expressed in adaptive development of form and behaviour.

This chapter has been largely a summary of Goodwin's views and has been free of mathematical descriptions. The reader should know however that theorists, such as Zeeman, Eigen, Haken, Grossman, and also Goodwin himself have developed mathematical models of what I have been explaining verbally. Like other area's of science, theoretical biology is well served by the interaction of mathematical modelling and the actual observation of reality.

3.7 Synergy

The question: what is life? has occupied poets, scientists and priests. In the next chapter a summary of the evolution of matter and of life will be discussed (based on E.Rubenstein, a medical scientist). We now have a definition of life: a memory (assembly of knowledge) in the form of adapted forms and functions. Cognition about the environment is collected and encoded in living organisms determining the way they behave (move, explore, select, refuse, accept, ingest, and assimilate). The next question is how this "written" record develops, i.e. the gradual apposition of encoded knowledge in living systems.

A substantial part of the answer is: by synergy, the process of demand and response between living organisms and their changing environment. The meaning of the word synergy has been subject to modifications over the years. Its literal meaning is working together. Co-operation naturally occurs in many different contexts. Synergism in theology for instance means that 'divine grace and human will co-operate in the work of regeneration' (Webster's International Dictionary). In a medical context it may mean that two agents add to each other's effect, such as drugs or enzymes.

In a general sense we define synergy as: self-organisation by alternating messages that oppose and complement each other. Synergy is the outcome of dialogue. For an example think of the chemical oscillations introduced in 3.1. Messages interacting in this way are said to be in "dialogue", displaying information flows in two directions which mutually affect each other and are bound to finally reach an agreement. It is specifically the term dialogue that has aroused much controversy. It is understood as "conflict". If conflict is followed by "reconciliation" that interpretation is correct. Correct, at least in social interactions where conflicts which are not immediately reconciled can persist without being life-threatening. However on fundamental levels of life a persisting conflict is unthinkable: conflicting motives have to come to an agreement without delay for life to be sustained. The resistance against the dialogue concept is understandable because until recently a narrow interpretation of dialectical forces in society was in use in communist theory. Kenneth Boulding in his book Ecodynamics (1978), has pointed out that there is much non-dialectical development in human society. However, the examples he gives of non-dialectical development, are on closer inspection clearly the result of dialectical (synergic) interactions. The difference is perhaps not one of definition, but of the broad (distant) versus the close (proximal) view. Looked at superficially a new design of a dress or a car may seem to be the product of a master-designer. A closer look at the creative process will show that during the fashioning trajectory there has been a continuous dialogue between new technical possibilities and public demands and expectations, a purely dialectical procedure of modifications competing with each other and being submitted for selection on the basis of quality, or expected sales.

A similar paradox has been described in an article "Instruction versus Selection" by the eminent immunologist N.K.Jerne with regard to the development of the immune system. From a distance it seems that the system is instructed by the environment to make properly fitting antibodies. This was the distant, "macroscopic" position of immunologists in the first half of the twentieth century. Discoveries in molecular biology gave a supplementary explanation, which is clearly one of dialectical development. It will be discussed in Chapter 5.

Synergy is the most a likely principle that sets evolution in motion and increases complexity. We have seen synergy in action in a first example: the alternating synthesis and decay of cyclic AMP (4.1). Together with its antagonist enzyme it is active in the morphogenesis and behaviour of Dictiostyleum. Its increase led to conglomeration of cells, its decrease by enzymatic decomposition accounted for the wave-like distribution, which in a later phase led to locomotion. Apart from this well researched example numerous chemical oscillators have been reported in other life-systems, interacting with each other to form complex networks or systems. In the second example, cartilage-formation in limbs (4.2), a dynamic equilibrium is established by hyaluronate that impedes clustering of loose cells, and hyaluronidase. The latter is an enzyme that dissolves hyaluronates so that aggregation can go on in the nodes where fibronectin concentration is high.

Networks based on synergy and oscillatory dynamics are manifest in life on all levels. We find alternating states and dynamic equilibria in:

Any organisation that possesses a self-righting mechanism maintains its equilibrium by fluctuating around a mean value. Disturbances from internal or external sources alternate with responses to neutralize the disturbance. Dynamic stability is a feature of oscillating networks.

Organisms are cognitive systems with a memory; they have collected their knowledge in the course of evolution.

Opposing tendencies meeting, working in alternation, and creating something new, better adapted and more complex, that is synergy in action. With this in mind we will study the immune and the nervous system. They fulfill vital functions in the mature vertebrate organism and possess the property of evolution, that is: they improve their performance by selecting the best fitting responses from each generation of variants. In other words: they are systems capable of learning. To begin with we must define the time-windows in which creative evolution takes place. 

Growth is learning at slow speed.

Learning is a rapid form of epigenetic development of the central nervous system

Goodwin 1967

 

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