Tuesday, September 06, 2005

Agar, Embryology and Evolution

Australian Cell biologist Wilfred Agar (1882 to 1951 biography here) described his book, “A Contribution to the Theory of the Living Organism” (published 1943) as his most important contribution to biological theory. Yet the book has had a negligible impact on his field, probably because of the vast distance between the foundational assumptions of biology which he proposed and those with which mainstream biology operates. Nevertheless, I think Agar makes some seminal contributions not only to alternative foundational assumptions for biology, but also in the application of these assumptions to embryology and evolutionary theory.



The central theme of Agar’s exposition is that organisms are made up of purposively acting agents. These agents are experiencing subjects. Agar refers to the agent which has overarching control of the organism (which in the human case would be referred to as the self or ego) as the Central Agent. He contends that individual cells are also agents which subjectively experience their environment (including influences from the Central Agent), though this experience may not necessarily be conscious. Thus, for Agar, the organism consists of a multitude of feeling subjects each acting for their own ends and with varying degrees of control over their environment.

In the case of individual cells the purposive behaviour is directed towards what he refers to as hormic goals which are simple, non-cognitive and immediate goals such as seeking satisfaction and avoiding dissatisfaction (such as aversion or attraction to certain stimuli). Agar uses the analogy of the hormic goals of cells with those of a wasp building it’s nest for the feeling of satisfaction it obtains through this activity, rather than for any intelligent purpose such as caring for offspring.

Agar leaves it as an undecided issue as to whether parts of an organism which may act as causal units, such as self-differentiating organs, may also be experiencing subjects.

Agars position on the organism as a society of experiencing agents is based on both empirical and philosophical considerations. He contends that the existence of human consciousness supports the view that experience must exist at a more basic level rather than appear magically out of nowhere. But he also sees empirical support for the idea in such things as trial behaviour and learning in single celled organisms and embryonic cells.

Bizarre as it may initially sound, the idea that each cell in our bodies may be an experiencing subject is not without some contemporary currency. For instance, the conjectures of Jonathon Edwards that consciousness is a property of individual neurons has recently appeared in the Journal of Consciousness Studies.

Embryology

Agar applies his theory of the organism as being made up of subjects to what he refers to as the cardinal problem of biology - embryonic development and morphogenesis. The issue of how the multifarious cells of the developing body differentiate and result in the formation of a fully functioning organism is a remarkable and perplexing phenomena. Agar addresses this problem with a comparison of the behaviour of embryonic cells with instinctive, goal-oriented behaviour. He lists the following parallels between morphogenesis and instinctive behaviour:

1) Embryonic cells, at least in isolation, exhibit trial behaviour which, Agar argues, implies purposiveness. For instance, he cites the aggregation of dislocated amphibian embryonic cells into a smooth ball as being the result of random testing movements which cease when satisfactory contact with other cells is established.

2). Both morphogenetic and instinctive behaviour are directed to hormic goals, which have biological consequences that were not the end in view of the organism carrying out the action.

3). Both brain fields and morphogenetic fields are stimulus fields, providing stimuli to which their constituent cells or agents make specific responses (as in, for example, the stimulation of motor neurones concerned with muscular action).

4), Embryonic cells have a stock of potential responses, only some of which are utilised in the course of embryonic development, much like the variety of responses to animals to sensa in combination with internal states gives rise to specific forms of instinctive behaviour.

5). The fact that embryonic cells have a variety of potential responses yet their descendant tissue cells are limited to specific responses has an analogy in learnt animal behaviour in which a specific response is induced by a stimulus, although at first the stimulus evoked a variety of responses.

6). If a portion of an organism undergoing morphogenesis is removed, the remainder may reorganise itself into a similar organism of smaller size (as in, for example, the reorganisation of a planarian worm from which a portion has been excised into a complete worm of properly proportioned parts). Similarly, where portions of the brain of animals have been removed, other areas of the brain may compensate and learning processes may be taken on by the remaining areas of the brain.

7). Both in embryonic agents and in the completed organism instincts appear and disappear by the process of maturation.

8). There is a parallel between the control of the activities of the whole organism through the central agent of the organism with the apparent ability of individual cells to act as purposively acting causal units.

Evolution

Although Agar’s schema does invoke a form of teleology in that the activities of cells are directed towards goals of achieving satisfaction, this teleology is an immediate one which is not directly related to the functioning of the whole organism. To quote Agar:

“ The acts of embryonic agents by which they attain their goals we conceive to be the acts of purposive agents. But we cannot suppose that their hormic goals include the biological consequences of their activities; that for instance the hormic goals of the agents concerned in the development of the eye include its preparation as an organ of sight…. The fact that the multifarious activities of the numerous embryonic agents, which moreover during a part of the embryonic process develop in essential independence of each other, produce a unitary organism in which organs function in ways which are by no means a continuation of the processes by which they were formed, is a problem of evolution.” (p 199)

Thus, the processes by which the functioning organs of an organism arise is a product of the natural selection of agents pursuing hormic goals which have incidental biological consequences for the fitness of the organism.

Agar thus sees evolution occurring through standard Darwinian processes. There is a difference however, in that the purposive actions of embryonic agents may allow the assimilation of developmental changes induced by mutations. As Agar puts it:

“On the assumption that embryonic sub-agents act purposively, if a mutation occurs affecting predominantly only one embryonic process, then the remaining processes will accommodate themselves to the new conditions as best they can. Each will produce an end slightly different from the old one, but functioning in a similar way - as a spider accommodates its web-spinning to the space available to it.” (p.115)

Thus the purposive acts of embryonic agents, perhaps towards the attainment of satisfaction achieved through symmetry, pattern or cohesion, has the by product of increasing the likelihood of functioning parts with survival value evolving.

This feature of Agar’s speculations can act as a counter to some Intelligent Design arguments which have contemporary currency. One of the most common criticisms of Darwinism by ID proponents is that it cannot account for the evolution and functioning of complex organs such as the eye. But when natural selection is acting on organismic processes which strive towards the achievement of hormic goals which have incidental survival value, the process seems less incredible. For instance, the evolution of the lens of the eye could be seen as a by-product of the satisfaction derived by embryonic cells of the eye in becoming part of a network of cells with a smooth, spherical shape.

Thus, Agar postulates an additional factor in evolution upon which natural selection acts which can deflate arguments for Intelligent Design.

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1 comment:

Adam Ierymenko said...

I said something rather whimsical and bizarre once when discussing development: "You are your cells' religion."

Please, nobody take this very loose metaphor too literally or seriously! :) But it does make you think a bit. It conveys something intuitive about how development and multicellular organisms really work.

Something similar I said once in a class on developmental biology: "so, the cells become a mouse because they are all really into doing this mouse thing. They're really into 'mouseing,' and what they do is figure out how to mouse by talking to each other and making sure that everyone is mouseing in the right way and all the parts are getting filled. 'Hey! if we're all gonna mouse, you need to be over there! ok!'"

It really does happen more or less that way. Calling the name of the end product a verb helps you understand development a lot better.