Chapter 9
- An Effort to Explain the Process of Body Formation

In the books I have had access to I have searched for data about different trhories about body formation. In the book by Stephen jay Gould, ‘The Panda’s Thumb’ [13], 1987, the author is studying the genesis of multicellularity at animals. But it appeared that the problem that was dominating his essay was the origin of different animals and relationship. Very little is mentioned about different theories about how multicellularity may have arisen.

According to Gould [14] there are only two established scenarios for body formation, but regrettably neither has been treated exhaustively. In the first scenario, called “the melting”, one group of protist cells were brought together. They began to live as a colony, developed a division of labor and developed finally an integrated structure.

In the second scenario, called “the section”, there arose cell departments within one sole protist cell. (A third conceivable scenario, repeated inability at the daughter cells to part after the cell division, has nowadays few proponents.)

I have not been able to comment the above as I am lacking the relevant knowledge. But I can barely believe that the problem body formation would be solved according to these guidelines.

- * -

In ‘The Ideas of Biology’ by John Tyler Bonner, p. 25[10], the transformation into multicellularity. “Why did single-celled organisms become multicellular? Why is it, if some groups found the unicellular existence so permanently advantageous, that all groups did not stick to it? The answer probably lies in the matter of the increase in size. Larger organisms can do things that are not possible for smaller ones; they live in different ways, and by becoming large a new world with new opportunities opens up. (…)”

Among the living multicellular organisms we find an abundant variety of different and from each others separated endeavours to increase the size.

That is interesting but does it not mean that the transformation to multicellularity also is being urged on by these efforts for larger size; behind the transformation into multicellularity there are presumably other causes.

Bonner describes further additionally on p. 121[11]: “Put in another way this means that originally a multicellular organism was a collection of unicellular organisms that were physically attached, but eventually, through selection and the need of improved efficiency of function, the division of labor became marked so that the individual cells were no longer separate organisms but part of a new, larger, and more complex organism. If one were to examine cell colonies that exist today among the algae, the protozoa, and other aberrant groups, one would find every intergradation from groups of individual unicellular organisms that seem accidentally stuck together to well-integrated yet primitive multicellular organisms.

This kind of observation leads to the old question of what is an individual, and the answer seems to be that there is no sharp division line between a group of cell individuals merge to form a true multicellular individual; there is a continuum between the two extremes.” On p. 28 [8] Bonner writes: “The more successful method of increase in size is to have a series of cells stuck together in a true multicellular organism. But even this can be done a number of ways: the cells can divide and the daughter products fail to separate, or there can be an aggregation of separate cells. Only the former has given rise to higher animals and plants while the latter is found, for instance, in a curious group of organisms called the cellular slime molds. Here amoebalike cells grow first, and these aggregate into cell masses after they have finished feeding.”

He thereafter describes the following process that strikingly resembles the behaviour of the slime molds of Ardray.

Any viewpoints upon the causes behind the body formation is not being given, except for the striving for increased size respective a development regarded as passing continuously from simple cell clusters into primitive multicellular organisms.

- * -

The statements that Dawkins has recorded give more motivated explanations to the body formation.

In “The Selfish gene” [16] is among others following stated: “Both animals and plants evolved into many-celled bodies, complete copies of all the genes being distributed to every cell. We don not know when, why, or how many times independently, this happened.”

Some authors use to use the parallel with a colony and are naming the body a cell colony. Dawkins himself prefers to think of the body as a gene colony and the cells as comfortable and practical working units serving the chemical activities of the cells.

Even though the organisms are gene colonies, they have undisputedly attained their own individuality with respect to their behaviour. An animal moves as a coordinated whole, as a unity.

The selection has favoured such branches that are cooperating with others. The intensive competition must have rewarded central coordination rather than anarchy within the common body. Nowadays the intricate, mutual co-development between the genes has gone so far that it is no more possible to identify the individual machine of survival due to its collective properties. Practically, it is generally most comfortable to approximately regard the individual body as something that “tries” to increase the amount of all its genes for future generations. And in “The Blind Watchmaker’ [18]: “It seems that, once the eukaryotic cell had been invented, a whole new range of designs became possible. Most interestingly from our point of view, cells could manufacture large bodies comprising many billions of cells”.

“A major step in evolution was taken when cells that had been produced by successive splittings stuck together instead of going off independently. Higher-order structure could now emerge,…”[19]

- * -

When reading the accounts of Dawkin I find rather much worthy commenting. The constant picture is that the development from cell to body is described as free from conflicts, almost always occurring almost by itself.

The idea of a cell colony is very close and seems to be the closest one can come concerning the active forces within a body. The word ‘cell colony’ gives an apparent impression of clarity.

But it is impossible to derive sufficiently strong forces from the colony concept that are able to account for development and reproduction. A colony is a phenomenon that is lacking a suffient identity of its own.

Proposals to replace the concept ‘cell colony’ with ‘gene colony’ are a track that can lead wrong. The cells are something more than working units for the chemical activities of the genes. It is the cells and not the genes that are actively being involved in the level rise process.

The obvious starting point for the solution of the problem of body formation has been the doctrine of evolution. Therefore it is often being spoken about that the selection has favoured genes that are cooperating with others and that the intensive competition has favoured central coordination to anarchy within the common body.

That there exist cells and bodies everybody knows. It seems therefore natural so imagine that “it only happens” when a body is forming. The problem is not visible.

The hypothesis of cell colonies is hence not completely satisfying; it does not contain any explanations why, it is only question of giving a name, a heading to an unexplained phenomenon.

Any hypothesis about how the body formation might have come about is accordingly not t be found in the account by Dawkins, but only notions about cell colonies and an effort to apply the doctrine of evolution upon the problem of body formation. But that way is, as I have shown earlier, not practicable.

Copyright © 1992: Per Olof Jonson, Bandhagen

rating: 3.00 from 1 votes | updated on: 13 Feb 2011 | views: 15664 |

Rate article:

excellent! bad…