Vertebrate brain theory

A large part of today's living beings shows a segmentation of the body. This is clearly visible in earthworms, but vertebrates are also segmented. This segmentation is called metamerism.

To this day there is no accepted theory about how living beings could have evolved with metamerism. We will develop such a theory in brief in this monograph.

All multicellular organisms possessed the ability to reproduce. Here too, as with the unicellular organism, there was both the sexual and the asexual variant. We look at the asexual reproduction in those multicellular organisms which we count to the second replication stage. They were created by the independence of single-celled colonies to independent beings.

From one multicellular organism several new multicellular organisms could be created by division or sprouting, which could be interpreted as (almost) identical offspring.

The sprouting (or division) was possible because in the multicellular organism a division of labour developed between the cells. Cells with the same work task concentrated in contiguous spatial areas, this was the beginning of organ formation.

Individual cell areas specialize in the production of sperm or oocytes. From these, the organs for sexual reproduction developed. Other cells specialized in food intake, digestion, excretion, respiration, energy production from food, etc.

Special cell areas also specialized in asexual reproduction. We can imagine these cell areas as budding zones. There the descendants of the asexual reproduction path were created by budding. Of course, the cell areas for asexual reproduction could also be given another name (e.g. Stolo in salps), we decide to call them budding zones.

Certainly it was also possible that the multicellular organism - for example through external influences (application of force) - disintegrated into several parts, some or even all of which had the ability to regenerate into a complete multicellular organism again. However, we concentrate on the budding zones whose cells ensured asexual reproduction. Here we are mainly looking at organisms that had only one budding zone per organism. To simplify matters, we think of the budding zone at the rear end of the living being.

The asexual reproduction of these organisms thus included the formation of a bud from the budding zone, which ultimately developed into a complete second life form. The last step was the separation of this second life form so that it became a descendant.

This separation was an important step, which was anchored in the genetic material and had to be controlled biologically somehow. If the coding of the individual steps in the DNA was linear in the order in which they occurred, then the code for the separation was again at the end of the coding chain. It is possible that sometimes this part was lost during DNA replication or was skipped due to special causes. Then a disruption occurred here, and thus a double being was created instead of a descendant. If the non-separated daughter was then also viable because it could take in food (or was supplied with food) and had all the necessary vital functions, this reproductive error was not particularly dramatic. Practically a (very small) colony of two identical creatures was formed, which remained connected to each other. If in the course of evolution such constriction disorders occurred repeatedly and became more frequent, they could manifest themselves hereditarily. Then the last step of the asexual reproduction process, the strangulation of the successor emerging from the bud, was genetically removed from the hereditary program and the emergence of two-segmental organisms manifested.

One could also speak of the fact that here a new living being consisting of two segments has arisen.

If we apply this budding theory to the tunicata and imagine that after budding both animals used a common intestine because the anus opening of the front animal remained connected to the mouth opening of the rear animal, the nutrition of both was ensured. If the blood circulation system of both was also connected, because the blood circulation of the parent animal initially fed the daughter animal and was not reduced afterwards, then, if there was no spatial separation, a double being consisting of two segments had developed, which used a common circulation and a common intestine. This being was now not a colony of two single beings, but a completely new, but segmented living being.

We assume that this double being, which we call a two-segment, was again capable of sexual and asexual reproduction. Since both segments were almost identically constructed, each segment possessed the organs necessary for sexual reproduction. However, asexual reproduction was only possible in the posterior segment, since the budding zone of the first segment had formed the second segment. Therefore only the second segment had a budding zone for asexual reproduction.

In the asexual reproduction of the two-segmented organisms, the budding zone of the second segment was able to form a new bud, which, according to the genetic program, became an independent living being and was finally also separated. The resulting descendant therefore initially consisted of only one segment and had to form a second segment first in order to become a complete two-segment organism. This program also had to be included in the genetic information in order to be passed on to the descendants.

A constriction disorder of the two-segmental segment could lead to the formation of living beings consisting of three segments. Should this process also become hereditarily independent, there was nothing to prevent the formation of three-segments. Not much had to change. The bud at the rear end of the living being already had the ability to form segments, now only the uncoupling had to be omitted and the three-segment was possible.

Certainly, this process of transition from a single-segment to a multi-segment took many millions of years, but it required no novelties, only the omission, the skipping of a step: the decoupling of the descendants produced by budding simply had to be omitted.

Thus, in this monograph we imagine the emergence of segmented living beings, which first consisted of two, then of three and finally of many segments. These segments shared the organs for nutrition and mass transport.

At this point it must be mentioned that both segmented animals and segmented plants may have developed in this way. In plants, it was also possible that each segment (and thus also the starting organism) had several budding zones. This could explain the branched form of ferns, trees and many plants.

What evidence could support the theory developed here?

Since the tunicates (Tunicata) represent the simplest chordal data, we begin with our circumstantial search with them. This requires a review of the physiology of the tunicates. They already have a generational change, in which asexual and sexual reproduction alternate. The asexual reproduction happens by budding.

As a special feature, colony formation occurs in several species during budding. The offspring created by budding then remain connected to each other. In some species there is even a division of labour. The mother animal then serves to feed the buds, which in turn produce eggs or sperm and thus ensure the offspring.

Some species of tunicates (salps) form cord-shaped colonies in which all animals used a kind of common gut. Each animal is connected to the next one in such a way that the gill cavity of the predecessor is connected to the gill cavity of the successor by an entodermal tube, see [121], page 72. There it says, among other things

"The endodermal tube, which will soon recede, is accompanied on the upper and lower side by a blood vessel lined with endothelium, which is connected to the blood vessels of the oozoid, from which the daughter individuals are supplied with nutrients in this way. In the upper vessel, the blood flows towards the tip of the stolo, in the lower one back to the mother."

  This structure of interconnected salps could well be regarded as the preliminary stage of a new, independent living being. A common blood circulation is a strong argument for this.

Therefore, in this monograph we propose the thesis that the multicellular organisms of replication stage 2 - which developed from unicellular organisms through colony formation and independence - now themselves formed colonies of similar, multicellular organisms. Colony formation was gradually incorporated into the genetic code and became hereditary. Thus, a new type of living being was created, which initially consisted only of a series of already existing multicellular organisms. Each individual being in this colony group represented a segment, the whole being therefore consisted of a series of interconnected segments which, at least in the beginning, were basically the same as each other.

We will refer to such creatures as creatures of replication level 3. We will refer to these beings as segmented beings.

Definition: Creature of replication level 3:

In this monograph, we refer to the living beings created by the colonies of replication stage 2 beings becoming independent as replication stage 3 beings or as segmented living beings.

  Thus, the process of colony formation and the independence of the colonies into new, independent living beings occurred twice in evolution. First, the simple multicellular organisms formed from colonies of unicellular organisms. Then the segmented organisms formed from colonies of similar multicellular organisms.

We remember that the creatures of the first and second replication levels could be both animals and plants. The question is whether this could also apply to the beings of the third replication level. Obviously, there is much to be said for this.

We noted in the previous chapter that in creatures of the second replication stage the budding zone could possibly be present several times. If there were three budding zones, three new offshoots would form on the mother being by budding. In creatures of the third replication stage these would stick to the mother being. If each of the three new daughter creatures had three zones of budding, each of them could form three parts again by budding. This process could be repeated more often. In the end, a completely branched living being would emerge, which would be similar to a fern. It is therefore possible that higher plants could be regarded as organisms of the third replication stage, which are formed from elementary predecessor plants by sprouting, whereby several sprouting zones per segment are possible.

Here it becomes understandable why animals most probably have only one budding zone. Animals are mobile creatures, and if they were to branch out like trees, it would be impossible to coordinate the movement of the individual segments. If, on the other hand, the segments form a chain, an exchange of information via nerve cells can make possible the well-ordered movement of the entire animal from individual segments, e.g. in the millipede. This exchange of information, which is also supplemented by an exchange of substances (e.g. via a common blood circulation, etc.), can be excellently explained with the segment model. In particular, the development of the vertebrate brain can be explained here in a comprehensible way, as will be shown in this monograph.

Nevertheless, colony formation by other means cannot be ruled out. For example, it is quite possible that sponges were initially multicellular beings of the second replication stage, which became beings of the third replication stage through colony formation and independence. In this case, colony formation would have taken place spatially in all directions, so that segmentation would no longer be detectable.

It is not always easy to distinguish colonies of replication stage 2 organisms from replication stage 3 organisms when looking at a particular specimen. However, if you look at several successive generations, the distinction becomes easier.

In organisms of the third replication stage, segmentation has become part of the genetic code.

In this monograph we assume that the DNA of a living being not only has a control function but also a protocol function. This means that essential changes in the individual life of a living being are (presumably) also recorded in the DNA and passed on to the descendants. If, for example, living beings are moved to a small desert island where there is a shortage of food, they will become less large. The lack of food will then possibly be recorded in the DNA. This special feature can therefore be passed on to the descendants via the DNA, so that they also remain small. Similarly, information about pathogens that were previously unknown to the body could be included in the genetic recognition code and make the offspring resistant to them.

The assumption of such a protocol function of the DNA allows the explanation why budding is included in the genetic program with a lack of separation, which ultimately leads to segmented organisms. The strangulation disorder is logged and also occurs in the offspring. If it is statistically rare, only a small proportion of the offspring will inherit this strangulation disorder during sexual reproduction according to Mendel's laws, the remaining offspring will be unsegmented. But if these numerically inferior offspring with segmentation predominantly mate with each other, this strangulation disorder will manifest itself more strongly. Ultimately, a new species - the segmented variant - may emerge, possibly because the unsegmented animals are smaller and can be eaten more easily or have another selection disadvantage.

The protocol function of DNA would then also be responsible for ensuring that the same algorithms are used in the sexual reproduction pathway as in the vegetative area. Already in the fertilised egg the genetically recorded developmental path would be taken. Thus, after fertilisation of the egg, one would observe how a budding zone is formed in the embryo from which the individual segments of the living being gradually develop.

In more highly developed species, this budding zone would then no longer be explicitly perceptible during embryonic development; instead, an elongated, wedge-like structure would already be formed, which would anticipate the shape of the future living being and further differentiate and segment itself.

The inclusion of segmentation in the sexual reproduction pathway is ultimately the distinguishing feature that determines whether a colony of beings of the second replication stage is merely a colony of beings of the second replication stage or whether a segmented being of the third replication stage already exists.

Assuming that vertebrates are derived from tunicates (tunicata), the larvae produced in the sexual reproduction process would also have to develop a segmented structure in accordance with segment formation during evolution, if the adult animals were also capable of segment formation. The existing chorda of the larvae would be included in this segmentation.

It can be assumed that the segmentation, i.e. the independence of colony formation of the organisms of the second replication stage, will have occurred several times and in parallel. In this respect, segmented living beings - whether plants or animals - are not all directly related to each other simply because they show segmentation.

In the case of the tunicata, the segmentation of the animals probably led to the development of the vertebrates. Here, too, there were certainly parallel developments. For example, some species of salps are life-bearing, others do not have this ability. Likewise, vertebrates also have egg-laying and life-bearers. A splitting up can therefore have occurred very early.

If the segmentation ultimately affected both the parent animals and their larvae produced by sexual reproduction, then these larvae also had such segmentation. This means that segmentation was brought forward from the adult stage to the embryonic stage.

The formation of such multi-segmental structures in the adult stage can be observed in real life in salps, which belong to the tunicates. Whether their larvae are already segmented wind cannot be decided here. But the developmental theory outlined here can explain why vertebrates are both chordates and segmented. Asexual reproduction by grafting, in which the individual animals form a new, segmented organism, and in which grafting is advanced from the adult stage to the embryonic stage in the course of evolution, would be suitable for producing segmented vertebrates. The chordae of the embryonic stage of the original tunicates would be preserved and would ultimately develop into the vertebral column in vertebrates, while the metamerism of the segment animals would be preserved.

And since there are already livebearers among the salps, some of the segmental animals that emerged may have retained the ability to give birth to their offspring alive.

In general, it could be assumed that the various tunicata developed differently on their way to becoming segmental organisms. It is also possible that they developed into segmented plants in which cellulose provided the external stability.

The strength of the early segmented animals may have been improved by new structural elements in the course of further evolution. Some of them might have formed an outer skeleton - made of chitin, for example - from which the insects, which are all segmented, emerged. Others might have formed a calcareous outer skeleton so that, for example, crustaceans could develop. With an inner, hydrostatic skeleton, the various segmented worms could be formed, which still populate the earth today. Finally, an inner skeleton could also have been formed from cartilage and later from bones, so that the likewise segmented vertebrates of various genera could have developed. The early chorda thus developed into the segmented spinal column.

This would explain why genetic research provides such consistent results, for example, with regard to the Hox genes for the most diverse animal species. Hox genes are responsible for structuring the body. And here we find very large analogies between flies (Drosophila) and mammals, for example.

In some of the segment animals, the formation of segments can be directly observed during embryonic development in the egg. For example in annelids or insects with low plasma eggs. In the latter case, a short germ develops from the germinal system.

  "A short germ, such as that of tachycines, for example, consists only of the anterior head (without jaw segments) and a preanal segment formation zone which subsequently produces all segments (including those of the gnathocephalon) teloblastically, as is basically the case with the trochophore of the annelids". [119], page 212.

  In more highly developed segment animals such a segment formation zone is no longer directly discernible.

The segmentation allows us to explain in this monograph the formation of the vertebrate brain in the course of evolution. That is why it has been treated in such detail here.