Theoretical contributions

An introduction to the origin of an integrative unit in phylogeny (as an example, an initial hypothesis of the origin of the animal)

(A summary by the FIBE of the unpublished work of Faustino Cordón “Origen y evolución de la secreción gástrica. Una contribución al estudio del animal por su origen” (Spanish), 1964, and "Conversaciones con Faustino Cordón sobre biología evolucionista" (Spanish), by A. Núñez, 1979, pp. 199-242)

This introduction aims to show the order of application of some concepts of the theory of integrative level units in order to address the phylogenic emergence of the originary unit of a new biological level.

Faustino Cordón developed his theory of the emergence of a unit of a higher integrative level in the process of evolution by carrying out a detailed study of the origin of the cell from an evolved association of proteins. However, to introduce his interpretation of the emergence of a unit in its phylogeny, we have chosen to present his provisional hypothesis on the origin of the animal because 1) as it is a work that is not fully developed, it favours the summarized presentation of basic concepts of his theory, 2) the facts and data of the animal are nearest and most familiar to us, and 3) it will be easy for us to follow Cordón when he induces the physical nature of the animal unit (experience).

The biological problem of the origin of the animal occurred to Cordón in the 1960s as a result of an experimental work that was apparently far removed: obtaining an antacid for the treatment of gastric hypersecretion. The large amount of empirical and experimental data that are available on the ontogeny of the major types of animals will without doubt substantially modify this initial model of the origin of the animal. However, the incipient approach to this question may help us to show the order of concepts that allowed Cordón to consider and resolve problems beyond the horizon of present-day biology.

Some data on animal phylogeny and ontogeny regarding the origin of the animal

All types of living being are defined, among other characters, by a particular mode of nutrition, of trophism. Animal trophism consists of capturing masses of cells (originally minuscule plant residues) and incorporating them into a cavity defined by an epithelium of cells, into which the specialized digestive cells introduce enzymes that degrade the matter ingested to make it directly usable by the cells of the animal soma. Accordingly, in the first animal (as in all animals) the nucleus of its incipient soma would have to possess a digestive cavity with digestive cells, sensory cells, muscle cells and nerve cells to allow it to capture, introduce and digest multicellular nutrients. (Cordón considered nutrients to be the nucleus of the environment of the originary animal; this environment gradually expands as the animal becomes more complex in its phylogeny and ontogeny, so the concept of nutrients used in this study should be replaced by the broader concept of the specific environment in more complex animals.)

There are no fossil records to trace the origin of the first animal, which must have occurred in the early Cambrian Period (600 million years ago). Thus, our data must be obtained by comparing the ontogenic development of the major types of animals, because it seems clear that the first animal must have been somehow homologous to a stage of the ontogenic development common to all animals.

The phylogenetic tree of animals

Animal phylogeny indicates that all animals come from a primitive form akin to the planula larva. A homologue of the current planula larva must have been the common ancestor of Coelenterata and Ctenophora (very related phyla, which Cordón interpreted as associations of cells with animal trophism but still not real animals) and to the class Acoela (from which the other phyla, which he considered to be true animals, derived).

The data on the most evolved associations of cells and the most primitive animals that Cordón studied suggested a phylogenic process from a supposed association of cells with cellular trophism -a homologue of the larva of very simple present-day animals- to the primitive animal. Cordón thought that the pre-animal association of cells must have progressed through the following stages:

1) An association of cells with cellular nutrition started to feed on animal nutrients (solid masses of cells) that it captured through animal action (a mechanical action proper to animals).

2) An animal stimulus was established among the cells of this association and it perfected the animal action of the pre-animal association of cells.

3) In the pre-animal association, the animal stimulus became differentiated into the efferent animal stimulus and the afferent animal stimulus due to the corresponding differentiation of its cells.

4) In the efferent neurons the intercalary neurons became differentiated, and their activity resulted in the creation of the first animal unit the first animal. As a result, the cell association was transformed into the first animal soma.

Below we briefly discuss each of these evolutionary stages.

1. The adaptation of an association of cytophagous cells to the nutrients proper to animals through an action proper to animals

Cordón proposed a few consecutive changes in the complex transformation (which must be situated phylogenically) by which an association of cells adapted to cellular nutrients must have started to live on nutrients proper to the future animal, yet without losing its status as a mere association of cells. To this end, he studied the planula larva.

The transformation of the present-day planula larva into an adult coelenterate

Let us consider the ontogenic transformation of the planula larva into an adult coelenterate.
The planula larva is solid, having no interior hollow space; it is an ectoderm of flagellate columnar cells that contain a mass of endoderm; and it swims freely using the cilia of its outer cells.

Soon, a space appears in the interior of the planula: the beginning of the future gastric cavity. Despite its free movement, this larva cannot be considered an animal because it has no nervous system and only has nerve cells that communicate contiguous cells with each other, in isolation. The duration of the larva’s planktonic stage of free movement is governed by factors that are still poorly understood, but during this stage it must live on cellular nutrients, i.e. its cells feed by directly ingesting small particles in suspension, which it digests intracellularly through digestive vacuoles.

After a time, the larva is transformed into an adult coelenterate: the larva adheres to a solid object at its widest end and becomes sessile, and its internal cavity opens outward through a mouth at the opposite end. According to Cordón’s interpretation, an adult coelenterate attached to the ground is the paradigm of the first association with animal nutrition: however inexact, it is a reflection of the pre-animal association.

In the adult coelenterate, the cells of the endoderm turn functionally inside and become differentiated into digestive cells, which introduce enzymes into the inner cavity in the first digestive organ. The cells of the ectoderm, which moved the planula, are transformed into muscle fibres (myonemes) parallel to the surface of the digestive organ; they are arranged lengthwise and become a preliminary muscular organ that gives general movement to the association of cells. Sensory cells specialize in receiving nutritional stimuli and are grouped in the oral area to form an incipient sensory organ; the sensory cells and their corresponding motor cells maintain their coordination through elongated neurons, in a preliminary nerve organ. In this way the cells that move the planula from one place to another in search of cellular nutrients organize themselves, sacrificing the movement to adapt the sessile association of cells to capture solid animal nutrients through joint contractile movements, to envelop them in the digestive cavity, to digest them into cellular nutrients to the benefit of all the cells (which share it out in an orderly way), and to expel the waste.

According to Cordón, this association of cells, which digests animal nutrients in an internal cavity, is not an animal, because it continues to apply exclusively the individual experience of its cells in its cooperative action.

Based on the data relating to the transformation of the planula larva into an adult coelenterate, Cordón proposed the following steps in the first stage of the evolution of an association of cells towards the origin of the animal:

The planula larva and the adult coelenterate

1) In a small association of phagocytes, some cells became specialized in perceiving stimuli of the presence of remains of cells suspended in the water, and others became specialized in moving the association towards these remains with their cilia. The immediate proximity to the nutrients would enable each cell of the association to ingest them and digest them intracellularly through digestive vacuoles. (In essense, this association of phagocytes must have resembled the planula larva).

2) If we consider, first, that this association must have been exhausting a degraded cellular nutrition suitable for its phagocytes and, second, that multicellular remains that could not yet be used by this association would progressively accumulate, we can induce (and there are data to guide this in animal phylogeny and in the ontogeny of representative animals of species) some transformations that this association would undergo to adapt to animal nutrients.

One of the changes that must have occurred in the association of phagocytes to improve the use of the nutrients formed by masses of cells was the specialization of some phagocytes in expelling, through digestive vacuoles, the enzymes that previously acted intracellularly, and thus digesting the multicellular nutrients outside the cells; the degraded nutrients would be assimilated suitably by each cell of the association.

3) In this pre-animal association, successive selective advantages could have led to structural adjustments such as the following:

• The accumulation of digestive cells in a limited area of the association, so that they acted appropriately on the external nutrients (of increasing size) to digest them.

• The gradual intussusception of this area to avoid the loss of the digested nutrients (or their use by other competing associations), so the digestive cell (the digestive function) must have formed the digestive system, and not vice versa, and the possession of the digestive organ would convert the previous association of cells into a pre-animal gastrula.

• The adaptation of the ciliate motor cells of the association to form muscle cells, which provided the association with an integrated movement of ingestion of animal nutrients, would force the association to become a motionless gastrula. This sessile association with the form of a contractile sac must have included the following groups: 1) the sensory cells in the first preliminary pre-animal perioral sensory organs (taste and touch); 2) the motor cells in the first preliminary peristaltic muscle organ; and 3) the protoneurons, which would relate the sensory cells with the motor cells in the first preliminary pre-animal nerve organ.

With the successive differentiation of these four types of cells, the cell association must have experienced the changes of structure. From being an association with cells moving towards cellular nutrients, it became an association that released digestive enzymes onto the nutrients to degrade them so that they could be used by all the cells of the association, until it became a sessile association of cells capable of incorporating these nutrients by contractile movements and digesting them in its interior. It thus began to perform a new type of mechanical action, of an animal nature.

2. The emergence of the animal stimulus

In the situation described above, the need to refine the mechanical capture of the multicellular nutrients acted as a selective pressure to produce the following changes:

a) The sensory cells arranged themselves uniformly around the mouth of the sessile gastrula and refined their perception of the nutrients when they came into contact with them.

b) The motor cells arranged themselves in rings -first one, then several- located so as to provide the gastrula with joint movements for the mechanical capture of solid nutrients in suspension.

c) The protoneurons adopted an elongated shape to mediate between the sensory ring and each of the motor rings. Each protoneuron had terminations at the ends that allowed it to receive stimuli from its sensory cells and transmit them to its motor cells. The orderly situation of the sensory and motor cells forced the protoneurons to gradually take on a parallel arrangement, forming cylindrical surfaces that linked the sensory ring with each motor ring.

d) The sensory cells, protoneurons and motor cells were coordinated to make increasingly better use of the new nutrients.

The histological structure of the planula larva and the adult coelenterate

Let us consider in particular the activity of the protoneurons.

The increasing size of the association, as a consequence of the solid multicellular nutrients of increasing size, forced the protoneurons to take on an elongated shape and uniform length, and forced all those cooperating in a type of movement to arrange themselves in parallel to link the cells of the sensory ring with those of one of the motor rings.

Through the dendrites of the end related to its sensory cell (or cells), each protoneuron received molecular stimuli emitted by this cell (of an intensity proportional to that of the nutritional stimuli) and transmitted them through its other end to its motor cell (or cells). The transmission of the activity from the sensory end to the motor end of the protoneuron caused a metabolic current to run along its whole length. Because of the elongated structure of this cell, this caused electric currents to run along it.

Hence, arranged in a bundle, the protoneurons produced parallel electric currents triggered when stimuli were transmitted from their sensory to their motor cells. It is known that the oscillations in the intensity of all electric currents cause a magnetic field perpendicular to their direction, so the variations of the electric currents produced by the changes of activity of the protoneurons established the corresponding magnetic fields. The activity of all cells causes oscillations of micro-electric currents that produce magnetic fields, so those of the protoneurons would be a special form of something pre-existing in all cells. However, only in the case of the protoneurons, elongated and grouped in parallel, do these cellular magnetic fields become potentially perceptible to other adjacent protoneurons. The organization in parallel and the simultaneity of action of the protoneurons would cause these magnetic fields to coincide in space and lead them to jointly compose a common magnetic field as a secondary effect of the activity of these cells.

Hence, the growth in size of the association (an indirect consequence of its nutrition) forced the protoneurons to elongate, and the organization of the protoneurons in parallel caused the magnetic fields (associated with the electric membrane phenomena taking place in each one of them) to form a single magnetic field, whose oscillations 1) reflected the changes of activity of the protoneurons in the bundle and 2) produced distortions in the electric currents of each protoneuron, so the oscillations of some protoneurons would be perceptible by others in the group. The arrangement in parallel of sets of elongated cells specialized in transmitting stimuli from their sensory cell (or cells) to their motor cell (or cells) would have an unforeseen beneficial consequence: the protoneurons could simultaneously perceive the initiation or the cessation of the activity of any protoneuron in its bundle as a consequence of its new associative activity (the influence of electric phenomena in the common magnetic field of all the protoneurons of the bundle, and that of the common magnetic field on the oscillations of the electric currents of each one) much more rapidly than through the sequential stimulus between them (the release and capture of dissolved molecules).

If each protoneuron exercised its original function (transmitting molecular stimuli from its sensory cell to its motor cell with the intensity established by the former) but waited (together with all those of its bundle) to start and stop it until the initiation or cessation of activity of a protoneuron that they all took as a signal, then the intensity of the stimulus released by each sensory cell would be faithfully transmitted by each protoneuron to its muscle cell, but the muscle cells would receive their respective stimuli in unison, with an instantaneous initiation and cessation. There would therefore occur a pulsatile (discontinuous) mechanical movement that was better adapted to the capture of solid multicellular nutrients in suspension.

According to Cordón’s first model of the origin of the animal, in this stage of the evolution of the pre-animal association, the protoneurons would be stimulated by their sensory cells but they would not stimulate their motor cells until a “signal” protoneuron did so. The disturbances caused by the activity of the “signal” protoneuron in the common magnetic field of the bundle would be the warning for all the protoneurons located in parallel to act simultaneously, guided by a much faster stimulus than the sequential one between cells: the new animal stimulus.

3. The differentiation of the animal stimulus into the afferent and efferent stimuli

The pre-animal cell association’s need to feed on multicellular remains of increasing size which arrived more and more discontinuously would have made each protoneuron of the association capable of performing several activities:

1) receiving stimuli from its sensory cell (or cells);

2) causing and perceiving electrical disturbances in the common magnetic field established by the parallel protoneurons of its bundle; and

3) stimulating the corresponding muscle cell with the intensity that it had received from its sensory cell.

Outline of the diversification of species according to Darwin

It seems that this plurality of functions of each protoneuron would create the selective advantage that each protoneuron became differentiated into two, an afferent one specialized in establishing the common magnetic field of the animal stimulus and an efferent one specialized in perceiving the variations of the common magnetic field of the animal stimulus. These two types of protoneurons, organized into two types of sets, would undertake different activities:

• The afferent protoneurons would receive molecular signals from their sensory cells but would only come into action when an afferent “signal” protoneuron started its activity. When this afferent “signal” protoneuron was activated, its electrical disturbances would be perceived by all the afferent protoneurons of the bundle and then, in unison, they would transmit the molecular stimuli received by each of them from their sensory cells to their efferent protoneurons until the afferent “signal” protoneuron stopped, with the result that all of them would establish a pulsatile afferent animal stimulus proportional to the nutrients present in the pre-animal cell association.

• The efferent protoneurons would receive the molecular stimuli of their corresponding afferent protoneurons, but none of them would transmit it to their corresponding cell muscle until they perceived the disturbances of the activity of the afferent protoneurons in the common magnetic field. The electrical changes caused by the activity of the afferent protoneurons would constitute the signal for all the efferent protoneurons of the bundle to start their activity simultaneously and in unison. Each of them would transmit to its corresponding motor cell the molecular stimuli emitted by its afferent protoneuron, until the afferent protoneurons ceased, with the result that among all of them they would establish a pulsatile efferent animal stimulus proportional to the intensity of the action that the pre-animal association was going to perform on its nutrients (and equal to the afferent stimulus).

Thus, each new afferent stimulus would be the objective reflection of the change of nutrients due to the previous action that the association made to it. (If in the previous moment the association had captured the expected nutrients, in the next moment there would be no change in the afferent stimulus; if in the previous moment the association had obtained more nutrients than expected, in the following one there would be a greater afferent stimulus; if in the previous moment the association had lacked nutrients, in the next one there would be a lesser afferent stimulus.) And each new efferent stimulus (proportional to its afferent stimulus) would be the objective reflection of the intensity of the action that the association was about to perform on its nutrients.

According to this model, the functional differentiation of the primitive protoneuron into an afferent and efferent protoneuron would enable the two new types of cells to emit and perceive more exactly the two types of stimuli between cells in which they are specialized (dissolved molecules between contiguous cells and disturbances in the common magnetic field of the nerve cells in parallel) and thus increase the effectiveness of the pulsating actions of these cellular associations on solid nutrients.

4. The differentiation of the intercalary protoneuron from the efferent protoneuron

The exploitation of the trophic environment by the progressively better adapted cellular associations would lead nutrients of an increasingly variable size to reach them with increasing discontinuity. In this situation, it seems that the refinement of the comparison of the change in the state of the nutrients between one action and the next would have to be a selective advantage of these associations. The differentiation of a third protoneuron, the intercalary protoneuron, may have contributed to this, as it would help to establish a reference between one action and the next one that would expedite the activity of the efferent protoneuron.

To distinguish the discontinuous arrival of nutrients, the intercalary protoneurons would specialize in maintaining a common magnetic field of fixed intensity that would emphasize the arrival of each new afferent stimulus and thus help the efferent proteins to perceive it.

In the pre-animal association that gave rise to the first animal in evolution, the intercalary protoneurons would learn to cease their activity when the afferent protoneurons ceased to emit their stimulus. Hence, all the intercalary and afferent protoneurons would interrupt their action in unison, so the two magnetic fields (the fixed one of the intercalary protoneurons and the new afferent stimulus, both pulsatile) would be left to themselves and would merge into a single one, separate and ephemeral, resulting from what had actually been obtained in the previous pulsation.

When these two -now free- magnetic fields coincided in space and time, the new, brief, autonomous field that resulted would tend to seek its greatest transient stability (before being destroyed in the general magnetic field), and it would do so through the self-correction of its lines of force.

If the intercalary protoneurons learned to perceive the new lines of force of this brief, autonomous, self-corrected magnetic field and, as always, they maintained it for the efferent proteins to perceive it, these proteins would establish an efferent stimulus proportional to it, and different from the afferent stimulus of the pulsation. From this moment, between each two successive actions the link would no longer be each new afferent stimulus but this free magnetic field, which, in response to each new afferent stimulus, would react and establish a new efferent stimulus different from the afferent stimulus of the pulsation.

5. The origin of the animal, the emergence of the animal unit (experience)

It is a postulate of this model of the origin of the animal that, before disappearing (after serving as a guide for the new activity of the intercalary protoneurons and therefore becoming the new efferent stimulus), this autonomous and ephemeral magnetic field resulting from the interference between the magnetic fields of the efferent and the afferent stimulus of a pulsation -released, left to themselves- had an unexpected effect: the ability to become an agent, the animal unit (experience).

Cordón proposed that the instantaneous magnetic field of the animal unit, which is created pulsatilely by the simultaneous cessation of the activity of the afferent and intercalary neurons, must have two properties:

1) The ability to perceive the quantum state of its environment through the contrast between the effect that it really obtained in the previous action (the afferent stimulus from the afferent neurons) and the effect that it expects to obtain on the environment in the present action (the efferent stimulus from the intercalary neurons). This contrast may increase or decrease the interference of the vectors of force of the animal’s magnetic field and may therefore increase or decrease its ephemeral stability, which it has to perceive as a sensation of pleasure or displeasure, respectively.

2) The quantum capacity of freedom from the perception of the state of its environment. As a unitary magnetic field, the animal must possess the quantum ability to self-correct, trying to coordinate its vectors of forces in quantum attempts to stabilize itself and react to its disappearance in the Earth’s general magnetic field. Cordón considered the capacity of freedom of the animal to be the quantum of self-correction of its action on the environment, in accordance with the pleasure or displeasure of the effect caused by the previous action.

From the moment when the protoneurons established the higher unit, the animal, Cordón calls them neurons; accordingly, the efferent and afferent stimuli of the pre-animal association become the efferent and afferent stimuli of the animal, and the pre-animal cell association becomes the animal soma.

Outline of the probable phylogenetic relationships of the main groups of placental mammals

According to this model, as a living being, as an integrative unit, the animal has the capacity to perceive the favourable or unfavourable effect of its action on its environment and to try to make the most suitable correction. This correction is taken as a guide for its somatic cells with the goal of guaranteeing a stable cellular environment. The animal (a physical field common to all cells in nature but different to them and more tenuous) guides its somatic cells without knowledge of their existence, and the cells of the soma give rise to the animal and use it as a guide to their activity, without perceiving it.

From the origin of the first animal, its experience would become the link between two successive actions. Although the pre-animal association of cells took full advantage of the present environment, depending passively on it as an integrative unit of a higher level than the cell, the animal is able to perceive integrally a new environment constituted by a wider network of relationships and, in each moment, to actively anticipate its changes to ensure its own conservation.

At present it cannot be proven that an ephemeral magnetic field established by certain cells in certain conditions (from the instantaneous interference of two others, that of the afferent stimulus and that of the efferent stimulus) acquires, in the very short moment of its existence, the quality of becoming a living being, i.e. a focus of action and experience. We only have the general empirical fact that when every animal originates in its ontogeny, it becomes a new focus of action and experience that disappears when it dies, and we also have the experience of what we feel as animals.

However, from this initial model of the origin of the animal we can draw some conclusions that should be true in every animal:

1) The model of the animal as an integrative unit: it should have no alternative and must explain three phenomena that are essentially the same but that we perceive as different:

• the emergence of the animal unit in each moment, pulsatilely, from the activity of its somatic cells;

• the birth of an animal and the development of its behaviour and its specific structures during its ontogeny until its death; and

• the appearance by specific selective advantages of each type of animal in phylogeny, without the characters acquired in each animal ontogeny being inherited.

2) The animal and its specific environment: the reality surrounding the animal must be an orderly and stable process that has the precise qualities for being the object of its action and experience. When the animal emerges in evolution, it establishes a fabric of new relationships, its new environment (the biosphere in the three states of aggregation of the molecule: liquid, solid and gas), which the cell cannot establish in response to its environment (masses of water with dissolved molecules). In this new network of processes that the animal perceives, it initiates a new stage of the process of evolution of reality.

3) The animal and the cells of its soma: as stated above, the animal as an integrative unit is a magnetic field that indicates the intensity of the activity of its somatic cells without perceiving them. The somatic cells, which have a qualitatively different physical nature, take the animal as a guide without knowing its existence; and the cooperative set of cells of the soma link the animal, in each moment, with its corresponding environment.

Therefore, from the moment when the animal emerges, we must consider the facts related to the animal, those related to the cells that constitute its soma, and those related to its environment, and we must try to perceive those that depend on each one of them and that evolve with it.

"Significación de la técnica de reflejos condicionados para entender el origen y la naturaleza de la actividad animal" (Spanish).

Antonio Núñez, Conversaciones con Faustino Cordón sobre biología evolucionista. (p. 199-240) (Spanish).