socratus wrote: > Maybe `the DNA in all of these is essentially the same.' > But cells come in all shapes and sizes . > Indeed.
Consider your word processor. Sometimes you're looking at the spell-checker, sometimes the main text entry area, sometimes an outlining tool perhaps. There are many screens that the word processor can show you, in all shapes and sizes. Nevertheless, it's the same source code. Different parts are turned on and off, so what is produced looks different. It is exactly the same with cells. A neuron looks like it does because chemical and mechanical signaling from neighboring cells caused the machinery to engage the "produce a nerve cell" portion of the program. We've seen that moving a cell early enough in the process, before it's committed, will allow it to pick up the signaling in its new home. That's all stem cells are: not yet committed to a course of development. This is amazing, astounding even; it is a wondrous mechanism. But it is not magical. >> Second, >> I already said that probability theory in no way says that the >> development of a human child in nine months from a single >> fertilized egg is impossible. >> Therefore the existence of such a child does not at all mean >> somebody/something must be managing it. >> / Richard Norman / > It is your opinion or law that probability theory doesn't work > in biology ( cells ) and in astrophysics ( big bang ). > Socratus > He did not say that, nor imply it. The Big Bang is a rather unusual situation, and we do not understand exactly what the probabilities should be in that instant. We have, we think, a fair handle on what was probably happening a tiny fraction of a second later; probability calculations are very much involved in these calculations, and in cosmology in general, especially in the sorts of reactions happening at the subatomic scale. Quantum physics, at its core, probability theory in practice. But you were talking about cells before, a completely different topic and not related to astrophysics. Your terminology is ... surprising. Probability calculations are involved in random events, but the overall process of picking up signaling and activating or suppressing parts of the DNA program to create different cell types is not a random process at all. At a very low level, probability calculations come into play: Accidents happen, things move around in the cell, /this/ particular ribosome hooks up with /that/ copy of a protein instead of a nearby identical copy. And damage can occur at various steps in the process; i.e. something can go wrong. But the damage is rare, and the probability is not the major driver; the programming is. So, in a sense, the production of a developing human child is the result of probability; past a certain stage of fertilization, it's the main chance that is likely to result because of the mechanisms at work. > >> Actually there is something that does manage it: >> the workings out of the machinery of biochemistry and >> biophysics and molecular biology and developmental biology. >> / Richard Norman / There is a famous neurologist named Richard Norman, inventor of the Utah Array for connecting electrodes with neurons. Any relation? And I met a Richard Norman who is a professor in London when I was teaching some seminars at a college there. Ah -- I just recalled that the neurologist spells his name "Normann" -- a pity (no reflection on you) as my meeting him online would have a certain irony (or at least coincidence) because of some of my other activities. > Cells make copies of themselves,. . . > Different cells make different copies of themselves,. . . > Cells come in all shapes and sizes . . . . > Somehow these different cells are tied between themselves > and during pregnancy process of 9 months gradually ( ! ) > and by chance ( ! ) they change own geometrical form > from zygote to a child. > You are using "chance" in an odd way. It's not what's happening here. > Cells come in all shapes and sizes, and then . . . they are you ( !? ) > This is modern biomechanical /chemical point of view. > Whenever you assert the correct way of thinking about something, I am always amused. Here, you seem to suggest that "something magical occurs" is all we know about the processes being described. / D. Keith Howington / =================.. . -- You received this message because you are subscribed to the Google Groups "Epistemology" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/epistemology?hl=en.
