Reply to Dr. Richard part 1
But John, all you have done is outline a theory. It is fine as a hypothesis, as is the alternative baked bean cell movement theiory I have just invented.
If you want to convince me, do some experiments to show us cells moving using the waves you describe.
While you are doing this, please may I present an alternative hypothesis that has had some nice experiments done to support it:
Cellular Motility Driven by Assembly and Disassembly of Actin Filaments
What, specifically, do you disagree with in this article? It seems to me it gives a coherent picture of how the cytoskeletal model can drive cell movement.
Thank you for this posting and for the reference. I don't think it the best exemplification of the problems with this field but I will use it as an example.
There are a number of general issues here and I will have to deal with them in turn. They are
1. Scientific logic.
2. Observational evidence and the degree of certainty that can be ascribed to it and the kinds of observational data that can or cannot be seriously disputed.
3. Theory – here I do not mean your ideas, I mean secure theory, evolutionary theory and thermodynamics and their implications for the kind of thinking displayed in the Pollard and Borisy paper.
4. Information and data theory, which is more or less a branch of thermodynamics (though less secure) and its implications for organisms and cells.
Beginning with scientific logic.
Popper, as you recall, has it that one cannot confirm theories, one can only disconfirm them, falsify them. Science, in short, is an essentially negative logic and a negative way of thinking. One cannot prove one's ideas, one can only give reasons for rejecting reasonable alternative theories. As a scientist, I presume you know this already.
Many people just ignore this kind of thing and I do realize that, in practice, it is not always easy to apply Popper's logic. Nonetheless his approach is widely seen as the best and ultimate logic of science. You and other workers in this field may believe that some other mode of thought is appropriate. If that is your opinion, it would be helpful if you would say so.
Popper's logic imposes certain core expectations on scientific debate of which two are relevant here. The first is that a theory should be articulated with sufficient precision that it can make testable predictions. In other words, a hypothesis is not worthwhile unless it is at risk of being refuted. You may not construct a hypothesis that is so general or unclear that it is immune from contradiction and apparent contradictions should be addressed. Second, alternative theories should be acknowledged and the reasons for rejecting them given. My aim is to know the reasoning that leads to the rejection of the wave model.
I come now to the Pollard and Borisy paper. You seem to feel that this paper is relevant yet it does not mention or discuss the wave model at all and does not seem to imply any reasoning process that might make predictions that could contrast it with the wave model. I would like to know of behaviours, found in living cells, that are explicable or predictable from this kind of cytoskeletal model and but which are uninterpretable in terms of analogous wave models.
The Pollard and Borisy paper describes an elaborated form of the cytoskeletal model for cell structure and function. Its substantial content is mostly just pen and ink drawings and the evidential status of the various features found in those drawings is unclear. I cannot discern any falsifiable predictions this model makes about the behaviour of actual cells. The criticisms Bretscher used to level and such ideas were always valid – which is not to say that his own lipid flow ideas were any better.
For the benefit of people who are not too familiar with cells, I would like to give a picturesque summary of the ideas underlying Pollard and Borisy's version of the cytoskeletal model. Imagine that the cell is a tent. The cell's outer membrane is a cloth and the cytoskeleton is an internal framework across which the tentcloth is stretched. This paper asserts that the cell moves by disassembling this internal framework at the back of the cell, transporting the disassembled components to the front of the cell, and then reassembling those components. It is, I think certainly true that such a mechanism would move a cell but I do not know of any species that moves by any similar type of mechanism. I therefore find this kind of suggestion fanciful. (Other versions of the cytoskeletal model have the cytoskeletal filaments behaving rather like railway lines with engines running along them and carrying cargo. This is equally improbable and parts of it are also implied by Pollard and Borisy's paper.)
But what, exactly, does Pollard and Borisy's description predict? It does not seem to predict whether cells have waves or whether external particles will move backwards, forwards, round in circles or not at all. So it has nothing to do with the wave model. It does not seem to predict whether external particles will adhere to the cytoskeleton. It offers no clue about why cells move or how they decide the direction of their motion. I don't see how it leads to any reasoning process able to produce testable predictions and, hence, I don't see it as a hypothesis. In what ways does this work articulate a theory of cellular action at all?
As indicated above, I will shortly return to this topic but I invite Dr. Richard to look at the tent analogy above. I ask him to add to it, modify it, suggest an alternative, simple description that gets at the nub of mechanism he seems to believe in. I ask him to describe that mechanism, in the simplest possible terms, and to indicate the reasoning process whereby it can lead to testable predictions. I also ask that he address the wave model, which is what this thread is intended to be about. If he rejects that model, would he please explain the basis for that rejection?
