Vertebrate brain theory

ISBN 978-3-00-064888-5

Monograph of Dr. rer. nat. Andreas Heinrich Malczan

2.3  From the single-celled colony to multi-celled organism

During the transition from a unicellular to a multicellular organism, it is no longer necessary for each individual cell to have all the structures and abilities that were present in the original unicellular organism, but rather for the cells to specialise. In most cases, they do not gain new abilities, but their range of abilities becomes smaller.

The transition from unicellular organisms to multicellular organisms becomes understandable if one considers that unicellular organisms can also reproduce vegetatively by division. For example, the cell forms, very simplified, a new cell wall, so that two separate cell spaces are created. Before this happens, the DNA of the cell nucleus has to be doubled and distributed to two new nuclei. The separation of the two cells is done by a kind of strangulation, which is the last step in this process. If it is assumed that all steps to be carried out are coded linearly in the DNA in their chronological order, the strangulation of the two resulting cells would be located at the end of this coding chain.

If this pinch-off (to stay with this example) is incomplete for any reason, both cells remain connected. It is sufficient for this to happen if the last coding section - in which this pinch-off is provided - is not processed. It is possible that the end of such a coding chain may have been lost when the DNA is replicated or its replication is suppressed by other factors. Thus, after asexual reproduction, two offspring remain, which remain connected to each other.

If this occurs several times, a colony of cells is formed, which are mostly completely identical.

Such colonies can often dissolve back into their individual cells when the environment changes - for example when there is a lack of food. This can be observed in practice and often also deliberately induced.

In such colonies one observes now and then that the initially completely identical cells begin to differentiate. This is how cell classes with different functions develop in the colony.

It is conceivable that the ability to form colonies manifested itself genetically and became the standard for certain unicellular organisms over millions of years. If then the division of labour between the individual cells of the colony, which has occurred in the meantime, was also included in the hereditary programme and manifested itself in the chromosomes, then from a certain stage of development one could speak of a multicellular living being.

Essential characteristics were retained, such as the ability to reproduce sexually, as well as the ability to reproduce asexually, for example by division or germination.

We are giving these multicellular Eukaryota a new name, which will make it easier to distinguish them later.

Definition: Living beings of replication level 2:

In this monograph, we refer to the living beings that develop from the colonies of unicellular Eukaryota as living beings of replication stage 2.

The development of replication level 2 organisms would certainly have come to nothing if it had not brought considerable benefits. This already begins with colony formation. The main advantage was the strong increase in size. Multicellular organisms were simply larger and could not be eaten so easily by the existing unicellular organisms, because they exceeded them in size. Certainly it was possible that unicellular organisms developed methods to enter the interior of the multicellular organism and continue living there. This is how the first parasites could have developed. But the multicellular organisms also developed different strategies.

On the other hand, the unicellular eukaryota also found ways to survive in a world of multicellular organisms. An increase in size was a suitable means here as well, so unicellular organisms with huge dimensions also developed.

Ernst Haekel developed the theory presented here:

The theory that multicellular organisms probably originated from colonies of unicellular organisms goes back to the German zoologist Ernst Haekel. Molecular biological investigations support the assumption that plants, fungi and animals each originated from their own unicellular predecessors.

The independence of single-celled colonies to multi-celled organisms may well have occurred several times and in parallel during evolution. Then the multicellular organisms would no longer be traceable to a common ancestor. This is obvious, because there is already an unmanageable number of different species in unicellular organisms.


Monograph of Dr. rer. nat. Andreas Heinrich Malczan