A recent approach explains the existence of fundamental particles on the basis of so called 'superstrings' (Witten 1988). A superstring is assumed to look like a small tube that results from the 'rolling up' of a field-sheet. If the tube protrudes from a larger field-sheet, like a straw from a glass with orange juce, or if it forms an arch on a field-sheet, like an ear on a teacup, it is considered an 'open string'. If the tube forms a small torus (a doughnut-like shape), it is called a 'closed string'. When a closed string hits on a field-sheet is may attach to it and become an open string.
Although this is still a working hypothesis, scientists have the impression that superstrings are indeed fundamental. Anything with lower complexity supposedly is not structured in a way that it can be recognised as particle or quantum.
The emergence of the first closure type. The torus like field-sheet creates a system showing a separation between an interior and an exterior world: the superstring. In the operator hierarchy, this closure is considered the first major transition. It creates the closure type of the interface. The interface-closure recurs at higher levels in the operator hierarchy where it 'encapsulates' hypercyclic processes and creates new primary operators. The closure type of the interface can also be recognized in the quark confinement, the electron shell, the cell membrane and the sensory interface.
Superstrings are not static. Every superstring is surrounded by a cloud of small strings that continuously are snared off and reabsorbed. This cloud of surrounding strings is so dense, that it shields off the properties of the central string, which is the reason that for example the charge of a bare electron differs from one with cloud.
This first order emission-absorbtion cycle (sting, snared off part, string in altered state due to emitted part, string re-united with emitted part) is a special property of superstrings that forms the basis for a second order cycle that emerges when two of these first-order cycles interact and form a cycle of cycles, or hypercyle.
The quark-gluon hypercycle takes the form of a quark emitting and reabsorbing gluons and exchanging the gluons with another quark that goes through the same process. Gluons themselves can also split and reunite, which in principle can result in a second order gluon cycle. Quark-gluon and gluon-gluon hypercycles presumably were the dominant system type in the quark-gluon plasma of the early universe.
The emergence of the second closure type. The change from superstrings to quark-gluon hypercycles represents the second major transition creating a new closure type; that of hypercyclicity. The systems in the operator hierarchy showing hypercyclicity are also called 'pre-operator hypercyclic sets', or in short 'pre-operators'. The closure type of hypercyclicity can be found to recur in the hadrons, the atom nuclei, the autocatalytic sets and the CALM-hypercycles.
At very high energies, which is equivalent to small distances between particles (in the extremely hot, minute, early universe) superstrings are supposed to move freely.
At lower energy levels, the superstrings that represent quarks and gluons show a kind of condensation, called confinement, into small bundles of two or three quarks that exchange gluons at high rates. Responsible for this bundling is a very strong force that is caused by, what is considered the colour charge. Due to this force, quarks at low energy levels are never found alone. The reason is that -like the stretching of a rubber band- the colour force increases in strength when two quarks are pulled away from each other. At a certain point, the stretch-force becomes equal to the energy required to create new quarks. At that point, the colour force-field snaps and two new quarks are formed at the loose ends. Thus, no single quark can be created at low energies.
The colour charge comes in three colours, called red, green and blue and three anti-colours, called anti-red, anti-green and anti-blue. Quarks carry a single colour, and are therefore either red, green or blue. Anti-quarks carry a single anti-colour and are therefore either anti-red, anti-green or anti-blue. Gluons are colour neutral, because they carry a combination of a colour and an anti-colour (for example red/anti-green). It is quite special that gluons carry charge, because other force carrying superstings, such as the photons that convey the electromagnetic force, do not
carry charge themselves. A special property of gluons is furthermore that they can split on their journey through space.
The colour charge of a system of interacting particles must always be neutral and the colour charge must always be conserved in interactions between systems.
The emission of a gluon changes the colour of a quark, because the gluon takes with it a colour/anti-colour combination. Thus, when a blue quark emits a blue/anti-red gluon, the quark changes color to become red (because blue=red+ [blue+antired]).
The binding of exactly two quarks in mesons and three quarks in baryons is explained by the colour force. Identical colours repell eachother. Different colours attract eachother. The strongest attraction occurs between a colour and its anti-colour. This explains the binding of a quark and an antiquark in a meson. Mesons are not stable because a quark and antiquark quite easily annihilate eachother. Another strong attraction is that between the three colours red, green and blue. This explains the binding of three differently coloured quarks in a baryon.
Recurring first closure type. Quark confinement represents a closure that creates an interface (the colour field) around the quark-gluon hypercycle. This implies a recurrence of the interface closure.
The hadron is created by the combination of: 1. a closure creating hypercyclic interactions based on quarks and gluons, and 2. a closure creating physical units when the colour force 'confines' quarks into small bundles.
These closures together allow the emergence of the hadrons.
The third closure type. The emergence of the hadrons represents the third major transition and opens up the closure type of 'multi-particle system'. Multi-particle systems show recurrent interactions between particles of the same closure type and form a unit on the basis of connected interfaces. In the operator hierarchy, all operators that show multi-particle structure are called 'multi-operators'. Multi-operators at levels above the hadron are the multi-atoms and the pro- and eukaryotic multicellulars.
The adding of more quarks to a hadron (assuming this yields a stable system type) would not create a new system complexity. Higher complexity is possible, however, when hadrons exchange small mesons, the pions, and in this way create the nucleus.
The importance of pions as the cement between hadrons in nuclei has two reasons. One, pions are the lightest and therefore 'cheapest'
to produce. In fact, the swarm of pions surrounding a hadron is so dense that it represents the main part of a hadrons mass. Two, pions are the most stable of all mesons, which implies that they the best messenger particles, because they can bridge a relatively large distance before they fall apart.
Pion exchange is a very important process. Without it the universe would be devoid of neutrons. The reason is that any separate neutron shows a 50% chance on decay every 15 minutes. At this decay rate, and without new neutrons being formed, the universe would have lost all its neutrons within a few hours. By exchanging pions, the protons in the nucleus change state to become neutrons and the neutrons change to protons. Due to pion exchange, the neutrons are never long enough pure neutrons to show decay.
Nuclei are not alone in space. In the early universe they were surrounded by many quickly moving other particles. In principle, the positive charge of the nuclei attracts negatively charged particles, such as electrons, but at temperatures above 3000 0K the velocity of the electrons is too high to be captured. At lower temperatures, the electrons move slower. At that moment, an environment that contains electrons and bare nuclei will condensate to a state where the nuclei become surrounded by a number of electrons that fits closely to the number of protons in the nucleus. The result is a zero or close to zero net charge.
Recurring first closure type. The closure that creates the electron shell, can be regarded as the recurring of the interface closure.
The atom is created by a combination of the preceding two closures:
These two closures together allow the emergence of the atoms.
Fourth closure type. The emergence of the atoms represents the fouth major transition and opens up the closure type of the 'hypercycle mediating interface' (HMI). The name hypercycle mediating interface has been chosen to indicate that the atom is the first system in which a major transition causes a mediating layer around the hypercyclic processes.By surrounding the nucleus, the electrons effectively isolate the hypercyclic interactions in one atom from those in another. There exists one other HMI operator, which is the eukaryotic cell.
After the atom, a next step in system complexity must come either from a closure in the internal sturcture of the atom, which is not possible, or from the physical connection of atoms, e.g. a transition from atoms to multi-atom systems. Multi-atom systems show a recurrent interaction between atoms on the basis of their electron shell: they exchange electrons between their shells. This can result in strictly organised grids (in metals and crystals) or relatively loosely organised structures, such as organic molecules.
Recurring third closure type. The construction of multiatoms is based on recurrent interactions between the interfaces of operators with the same closure type. This implies a recurrence of the third closure type.
The adding of atoms to any multi-atom system may create closed interactions, an example of which are benzene rings. Regardless their complexity, however, these systems belong still to the multi-particle type. A possibility for a next closure type is offered by the reaction cycles of catalytic molecules.
The multi-atom structure of molecules allows three-dimensional structures. Some of these structures show catalytic properties; the enzymes. Enzymes (E) can to bind to a substrate (S) and modify it. The result is that the original enzyme is regained and that the substrate molecule (S) is changed into a product (P). This process forms a first order reaction cycle. In its most minimal form, a dissipative, self-maintaining reaction cycle emerges when the product of a first order reaction cycle equals the enzyme of a second cycle and vice versa. Such a second order reaction cycle is catalytically closed, and therefore considered as to be 'autocatalytic'. Yet, the reactions float in a larger chemical solution and show no structural system limit. Only a system limit that acts as an interface for the autocatalytic set would give the word 'autocatalytic' its meaning in a structural sense. Thus, where an autocatalytic set of enzymes shows only functional closure, it requires an additional closure to create a structural unit.
Recurring second closure type. The autocatalytic set shows a hypercyclic structure. This has occurred earlier in the evolution of system types. The first time it occurred was at the superstring hypercycle layer where hypercyclicity was introduced as the second closure type.
When, in a solution, two autocatalytic sets meet, they will mix and either float together or destroy each other. This lack of individuality is also problematic for recognising one of the possible outcomes of autocatalysis: reproduction. When an autocatalytic set produces enough material to make one or more copies of all its constituents it has in principle performed reproduction; it has created one or more 'offspring'. Yet, where are these offspring? They float in between the molecules of the 'parent' and cannot be separated from it. As diffuse entities, this type of offspring can neither be recognised as a unit, nor go their own way, nor experience individual selection. Clearly, what is lacking is a structural limit.
The autocatalytic set can obtain a spatial limit when the molecules form a kind of aggragate or when a surrounding surface mediates the hypercyclic reactions. A simple lumping of molecules creates a unit, but would still allow the mixing with other lumps and the disturbance of reactions by free interference of environmental molecules with the autocatalytic set. A surrounding layer that mediates the passage of molecules to and from the interior does not show such disadvantages.
This may be the reason that -as the next closure- nature has used a membrane that fully surrounds the autocatalytic set. It represents an interface that mediates the interactions of the hypercycle with what now has become the surrounding world. Once the cell membrane has formed, every hypercycle has become a structural unit that reproduces by forming new structural units and that can be recognised as an individual on the basis of it's unique autocatalytic set and membraneous system limit. The membrane also allows the submission of the cell as an individual unit to environmental influences acting as selection forces.
Recurring first closure type. The cell membrane represents an interface for the autocatalytic dynamics of the cell. This implies a recurrence of the first closure type.
The cell is created by a combination of the preceding two closures:
One consequence of autocatalysis is that the functioning of the cell goes hand in hand with the degradation of energy from the environment. Any 'whirlwind' system that maintains or even increases- it dynamics and organisation by degrading energy from its environment is regarded a dissipative system. This does not mean that all dissipative systems are operators. The structure of a tornado, for example, is created by the dissipation of an air-pressure gradient. Yet, a tornado does not conform to the first-next closure hierarchy of the operator hypothesis. A tornado is nothing more than a dissipative interaction system.
Another consequence of autocatalysis is that the system must 'struggle' to stay alive, because an autocatalytic set of enzymes represents a dynamic equilibrium state between degradation of the set on the one hand and maintenance and growth on the other. This equilibrium shows a minimum complexity boundary. If more molecules are lost from the set than are required for autocatalysis, the circular chain-reaction breaks down and the system sinks below its lowest complexity boundary and dies. To prevent death, or in other words to stay alive, the autocatalytic unit must balance the production and losses of the minimally required set of chain-reaction enzymes and in this way maintain itself. If no buffers are available the minimum requirement for survival/living is thus maintenance.
Autocatalysis may also lead to results that exceed mere survival. Under favourable conditions, the production rates of enzymes and other products will exceed the loss rates, which situation will lead to growth and may even cause the creation of a full copy of all constituents of the unit, which achievement marks the reproduction of the set.
Fifth closure type.The emergence of the cells represents the fifth major transition and opens up the closure type of structural (auto-)copying of information. The reason for this name is that, when a cell reproduces, it copies all its structural elements, including both the autocatalytic enzymes and the cell membrane, which implies that it has blindly copied all the information that it needs for its activity and survival. So far, there exist no SCI-operators with a higher complexity than the cells.
Prokaryote multicellularity is relatively rare and has remained primitive. This may be the result of the limited possibilities for complex coding of the prokaryote cells. In other aspects the discussion of prokaryote multicellularity does not differ much from the discussion of eukaryote multicellularity. For this reason it is not addressed separately in this text.
In prokaryote cells, all chemical activity takes place in a single compartment. This restricts further differentiation of the cell because any new enzymatic process has to be compatible with more and more processes and structures already present. New processes should especially not interfere with the genetic material in the cell, because this plays such an important role as a template for the production of functional molecules.
The latter problem can be solved when the main information carrying molecules of the autocatalytic set are protected by a surrounding membrane. This creates an extra internal interface, separating the copying of basic information from its translation into reactive compounds. The mediation of the hypercyclic information in the cell parallels the Hypercycle Mediating Interface (HMI) that was described as the structural emergent property of atoms. In analogy, also the possession of a nucleus by eukaryote cells is regarded as HMI. The nucleus by definition marks the emergence of organisms recognised as eukaryote cells. Regarding the nucleus from the point of view of information, it is interesting to see that the nucleus has kept much influence on the interpretation of its data. It contains the DNA that codes for most cell processes and (in the nucleolus), even prepares the RNA for the ribosomes that play such a crucial role in the translation of the information in the DNA.
Although this is not directly important for the operator hierarchy, which only focuses on the compartmentation of the hypercyclic reactions as the first-next closure, almost every modern eukaryote contains other compartments in addition to the nucleus. The most important of these are the mitochondria and chloroplasts.
Margulis (1970) has proposed a hypothesis which explains the presence of these organelles in cells as endosymbionts. According to this hypothesis the latter organelles have long ago entered primitive eukaryote cells as bacterial symbionts. The symbiosis is profitable for both parties. The endosymbionts are provided with a safe and stable living environment and the cell profits from the capturing of radiation energy by chloroplasts and from the oxygen based metabolism of the mitochondria. Oxygen based metabolism offers about twenty times more energy than is available via anaerobic pathways.
Several arguments support the endosymbiont hypothesis (Keeton and Gould 1993). One, the occurrence of facultative endosymbiontic relationships between prokaryotes and eukaryotes is rather common and offers a clear starting point for obligate symbiosis. Two, mitochondria and chloroplasts still maintain governance over the production of their own ribosomes. Three, like in bacteria, the chromosomes in endosymbionts are circular and not wound on special spool-like proteins. Four, mitochondria and chloroplasts divide by means of fissure without the interference of the spindle apparatus of eukaryotes. Five, ribosomes in endosymbionts resemble those in prokaryotes much more than those in eukaryotes. Six, mitochondria and chloroplasts are surrounded by two double-membranes, whilst eukaryote cells show only a single double-membrane. Together these aspects strongly support the endosymbiont hypothesis.
Recurring fourth closure type. The membrane of the nucleus represents a recurring of the hypercycle mediating interface closure type.
Eukaryotes don't show a nucleus all the time. Eukaryote cells pass through a non-nucleate phase during cell division. This implies that during this phase the cells change position in the operator hierarchy. Upon division they are temporarily thrown back one stage in the hierarchy to regain their position as soon as the nucleus has formed again.
Eukaryote cells represent the most complex operator type on the basis of single cells. The first-next closure involves interactions between cells causing multicellular life. Like in hadrons and in molecules this represents the emergent stage of the multi-operator. Multicellularity requires recurrent interactions between structurally linked cells. Both properties are necessary because unlinked cells are separate operators, whilst linked cells that do not depend on eachother for their reproduction form a colony.
Although multicellularity may be based on prokaryote cells, for instance in the blue-green algae, it can be observed in nature that the eukaryote multicellulars have had a greater evolutionary success. This difference is irrelevant for the text below, which only focuses on multicellularity as such, and not on the kind of cells that perform it.
What exactly defines a multicellular organism? To be recognisable as a unit system the interactions between the cells in any multicellular should create an emergent property that makes the interacting cells a whole in a structural and functional sense. To be a structural whole requires structural closure, which implies that recurrent structural links have to be created between the cells. Functional closure, then, requires recurrent interactions, which requirement is fulfilled by mutual autocatalytic dependence of the cells. A logical consequence of the above requirements is that any multicellular organism in principle must be able to perform autocatalysis, with which we refer to maintenance as a minimum requirement and growth and reproduction as potential consequence. The in principle is added because there may be external conditions (freezing) or internal genetic constraints that limit autocatalytic activity (worker bees) or place it under the survival minimum (death upon reproduction). This reasoning has led us to propose that multicellular operators can be defined as follows. A multicellular organism is a 'group of cells that show a combination of structural linkage and functional interaction causing at least one recurrent process that, under ambient conditions, is obligatory for the autocatalytic functioning of the contributing cells'. In cases were cells interact structurally and functionally but are not obliged to interact recurrently for their autocatalytic functioning, the cellular unit must be regarded a multicellular colony. Many multicellular systems, including mammals, pass through a single celled stage (the zygote) and multicellular colonial stage (for example the two, four and eight celled stage of a human embryo) before they develop into a multicellular organism.
For any organism, the minimal consequence of autocatalytic functioning is maintenance, the ultimate consequence reproduction. The multicellular unit should thus at least be capable of its proper maintenance, but may achieve growth (more cells) and reproduction (offspring) when the environmental conditions allow this. The requirement of maintenance follows from the dynamic equilibrium between formation and deterioration of the organism's compounds. Only after maintenance is safeguarded, can there be room for growth of the multicellular by means of division of cells and/or cellular differentiation. If the genes and phenotypic state allow this, the multicellular unit may eventually contribute directly or indirectly (for example in the case of sterile worker bees), to the reproduction of the autocatalytic sets of its cells. Although the above definition does not exclude any form of reproduction via clumps of cells, which even may possess various gene sets, the reproduction via unicellular stages is more favourable for evolution because it offers the possibility for selection to act on a single autocatalytic set. Yet, especially lower organisms, such as jellyfish and plants, frequently show different forms of multicellular offspring formation, for example in the form of buds, stolons, etc.
There are several reasons why the above general definition of multicellular operators allows many different system types. One, there are several ways in which cells can be connected. Two, are several ways in which cells may interact functionally. Three, interactions between cells may be based on different combinations of structural and functional possibilities. Four, as soon as organisms consist of many cells, the interactions between the cells may create hierarchies of emergent properties that may range from local to general. As will be discussed in more detail below, the interactions between cells may lead to two clear extremes. Relatively 'brittle' interactions are formed when the cells are bound in the least forceful way by means of membrane proteins, and when the diffusion of proteins is used for the intercellular communication. In this case, the overall system is a hardly more than a colony. An example hereof is the slug-like structure, called a plasmodium, which is formed when many individually dwelling cells of certain slime moulds come together. The cells in the plasmodium are kept together by membrane proteins, and communicate with each other via chemical signals. Together they produce higher concentrations of digestive enzyme hereby ensuring a better survival under low food conditions.They also reproduce together, for which purpose they obligatorily depend on the multicellular stage to initiate differentiation and the construction of a stalk on which spores are formed. At the other end of the spectrum, we find cells that communicate in a very intensive way via plasma strands. Such plasma connections are allowed through gap junctions between animal cells, through plasmodesmata between plant cells, through microdesmata in blue-green algae, and through incomplete cell walls such as in some fungi or developing insect eggs. Multicellularity requires, however, that only the plasma be connected, while the genetic material is retained in the cell.
The question can now be asked whether the above definition of multicellularity provides a practical and consistent way to recognise multicellular organisms? Clearly, the definition is selective enough to prevent the inclusion of interactions between cells that do not create an obligatory structural and functional interaction with respect to autocatalytic functioning. During the two-, four- and eight-cell stages, the cells of most vertebrate embryos are only loosely attached to each other by means of adhesion proteins. They can still be separated after which they will divide again to develop into a normal embryo. This is the explanation for the existence of twins that originate from the same zygote. Embryo cells in these early stages can even be mixed with cells of the same age from another embryo and develop to a normally functioning organism, a chimera, which consists of two genetically different cell types. Using the above definition, these four- to eight-cell stages must be considered multicellular colonies, since it is only after this stage that obligatory recurrent interaction processes are initiated and the cells loose their capacity to survive as individuals after separation. This also implies that as a consequence of sexual reproduction, any multicellular life form that starts its life as a zygote passes through a unicellular state and colonial state before it becomes a true multicellular life form. Consequently, and in accordance with current practice, any life form can best be classified on the basis of its highest complexity stage in the life cycle.
Several other cases require some discussion in relation to the above definition of multicellular operators.
One, although the above definition does not exclude an organism consisting of cells with very different autocatalytic sets, genetic conflincts about the transfer of preferred genetic material upon reproduction will generally select against chimeras.
Two, the success of a multicellular organism to maintain its organisation depends on its capacity to deal with prevailing environmental conditions, and to adapt or repair its organisation following damage. An example is the re-growth of a twig from a willow tree that is stuck in the ground. If the weather is not too warm, too cold, or too dry, etc. and the stick has enough buffered resources, it may survive long enough to regenerate roots and start growing, to become a willow tree. In extreme cases, even single cells of an organism can be induced to regenerate the multicellular structure. With a little help, for instance by means of in vitro-culture, this applies to many plant cells. The callus that forms, and the leaves and small plants that may emerge from it can be considered multicellular operators in the in vitro environment. Yet, they need roots and a certain size and strength before they have assembled all tools for internal interactions to survive as a plant in an outdoor environment, and development towards a reproducing stage. This shows that the interaction between the environmental conditions and the state of any particular multicellular organism determines which processes actually are obligatory for autocatalysis. The above definition of multicellular operators is explicit in recognising this relativity.
Three, lichens and plants with micorrhiza are 'multicellular organisms' which consist of two or more closely interwoven types of cells of different species. As lichens can also disperse in the interwoven form, it seems that they show common reproduction of the genetic material involved. However, these life forms can be classified as a symbiosis because the fungi show sexual reproduction without the genetic involvement of the algae.
Finally, multicellular organisms may produce structural material that supports their growth. This material is generally more persistent than the organism. Accordingly, a flash of lightening may split the bark and root system of a tree in two separate halves, which may continue to grow, supported by the common stem. Since the two tree halves show no intercellular communication anymore, they have to be considered separate organisms.
Recurring third closure type. The recurrent interactions and coupled interfaces (cell membranes) of the eukaryote multicellulars represent a recurring of the third closure type: multi-ness.
The multicellular system type forms a complexity barrier to evolution. The reason is that adding more cells creates larger muticellulars, but does not create a new system type. A possibility for a next closure type is offered by the recurrent interactions between neural cells. On the basis of interactions between nerve cells, groups of cells with closed excitation-inhibition dynamics can be created (first order interaction cycle) that subsequently interact in a recurrent way (a second order interaction cycle).
The advantage of nerve cells is that intercellular links between distant nerve cells allow many cells to become directly connected neighbours of each other. This way of 'communication' differs greatly from that based on random chemical gradients around cells. On the basis of stimulating and inhibiting nerve connections, groups of interacting nerve cells, called 'modules', can exhibit very special, novel dynamic properties. One example of such new dynamics is the categorising and learning function performed by the neocortical minicolumns. Another example is the oscillation pattern of 'interior olive' modules in the cerebellum, which function as neural metronomes (McCormick 1995). Several authors advocate that such modules are the basic functional units of the brain (Mountcastle 1975, Szentagothai 1975). I will henceforth refer to these neuron clusters in a general way as Interactive Neuron Modules (INMs). The categorising and learning functions and the metronome functions of such INMs represent a specific new first order- cyclic multicellular interaction that allows for the formation of an INM-hypercycle.
To explain the properties of INM-hypercycles we need to make a short excursion into computer simulations of neural networks. I will focus on a specific INM model used for simulating the neocortical minicolumns, which is called 'Categorising And Learning Module' or CALM. Murré(1992) and Murré et al. (1989, 1992) have published detailed descriptions of a CALM.
A disadvantage of the present CALMs is that an earlier learned task is forgotten during the training of a next task. To overcome this problem Happel (1994) has examined the possibility of coupling CALMs in a recurrent way. Due to the circular stimulation of CALMs in a recurrent network, the interaction strengths of the connections between the cells in a CALM adapt until a stable state, which supports dynamic patterns of nerve firing. These dynamic patterns can be periodic or chaotic. The type of dynamics depends on the history of the network and the input at a specific moment. The transitions between periodic and chaotic behaviour are relatively abrupt. For this reason the state space shows regions with almost discrete limits, causing a separation of observations in what appears as distinct classes. It is of marked importance that the state space of interactive networks includes the factor time in the form of short and long oscillation patterns. This implies a large extension of state space compared to any non-hypercyclic network that is based on feed-forward interactions only. As experiments of Happel (1995) show, the result is that the network dynamics can now capture the complexity of newly learned tasks with little loss of earlier experiences.
The emergence of the neural hypercycle is the first time that a pre-operator emerges as a consequence of the law of the penultimate level (Turchin 1977), which implies that it can be regarded as an internal differentiation of an already existing operator. The reason why this 'internal' closure must be preferred above potential cooperations between organisms is that the operator hierarchy is based on first-next closure steps. With the cellular multistage representing the last preceding closure, units of integrated neurons form the next closure. As the neural hypercycle represents the most efficient route towards a next closure, it makes any transition based on individuals inconsistent with the operator hierarchy.
The emergence of the neural hypercycle probably has taken place after the formation of primitive neural webs. There are several reasons for this.
One, it requires a certain amount of nerve cells to allow for the formation of neuronal modules and their interactions.
Two, for its survival an organism needs 'knowledge' about its environement. Plotkin (1994) defined 'knowledge' as any kind of system structure that enables an entity to act in relation to its environment. Using this definition, there is no inherent knowledge in CALM-modules of a newly born organism. The evolution of CALM-webs that lack the supporting environment of a pre-wired brain, therefore, is of little use to animals. It has a much higher fitness value if an animal can start its life with a more or less fixed neural circuitry that allows for reflexes. Due to selected-for, gene-based ontogeny, these reflexes will provide the right responses with respect to survival and reproduction. Predetermined structure also strongly reduces the time to learn something. Therefore, some predetermined structure in the brain is useful for the processing of stimuli even for organisms with the capacity to learn, because it reduces the search space in which the brain has to evolve the neural states associated with learned concepts. The above shows that learned behaviour, which is based on CALM-webs, must be considered to have evolved in a context of a hardwired brain producing most behaviour of the organism without that it had to learn for it.
Recurring second closure type. Based on a first order interaction cycle between neurons in the CALM modules and a second order interaction cycle between CALM's, The CALM hypercycle emerges. This represents a recurring of the second closure type.
The sensory interface has never existed as a separate entity. It co-evolved with the neural network in multicellular organisms, giving the CALM hypercycle information about its environment.
The sensory interface can be divided in an observing part, the 'perception interface', and an activating part, the 'activation interface'. The perception and activation interface are both oriented at the exterior environment and at the interior environment of the 'vehicle' in which the network resides. In organisms, the activation interface includes nerves that stimulate for example muscles for activity directed at the outside world and other nerves stimulating the neuro-secretory cells for internal regulation of physiological processes. The perception interface includes sensors directed at the outer world like eyes, ears, nose, etc., and all sorts of proprio-receptors (within the organism) such as chemo-receptors, stretch receptors, temperature receptors, etc.
Recurring first closure type.The emergence of the sensory interface represents a recurring of the first closure type.
The memon is created by a combination of two closures:
These two closures together allow the emergence of the memons.
I proposed to use the name memon for all systems that -as the result of a major transition- show a hypercyclic neural network with sensory interface. The name memon is chosen after Dawkins (1976) for cultural replicators that thrive in brains and the artificially manufactured products of brains - books, computers, and so on. In the operator hierarchy, however, the word meme is specified in more details to let it describe more precisely a whole range of memic entities that play a role in the functioning of memons.
Memons may be involved in the replication of various memic entities:
As far as I know, the above way of differentiating between various memic entities does not yet play a role in modern 'memology' (i.e. Wilkins 1998).
In principle, memic neural networks are not necessarily bound to organisms but can be housed in any kind of vehicle. A memon may even be built from other material than organic cells. In fact, any material may be used, and any other than electrical signal transmission, for instance light. What counts, is that the dynamic processes in a memon allow an equivalent of the neural hypercycle with interface.
Sixth closure type. The closure pair of the CALM hypercycle and sensory interface creates the memon. Inside the neural hypercycle, the neural interactions continuously lead to new states of the modules involved. As the modules in this process are capable of storing this information, these changes imply that the information content of the memon continuously is changed, even without inputs from the sensory interface. Additionally, memons of high enough complexity can analyse the usefulness of specific new ideas in relation to personal mental contexts in which these new ideas may be envisioned to play a role. Combining these two properties and because every idea represents a specific brain-state, the memon is capable of autonomous diversification and selection of states in its state space. For this reason, I have called this emergent property 'structural auto-evolution' (SAE). The emergence of (SAE) represents a major transition creating a new closure type.
The strict hierarchy of the operator hypothesis invites to an extrapolation of its logic to yet unknown evolutionary stages. Some considerations with respect to such predictions are discussed here.