Clear faults in Darwin's formulation of Natural Selection

Hi Syamasu,I'm just jumping in here 'cause you mentioned my name earlier in the thread...Peter is absolutely correct in his post #18 where he says:

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Variation is not essential to NS ... but without it the net result is either a slide into extinction or rises in population numbers to levels supportable by the environment.

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This is what I've been saying to you all along. In fact, it is a fairly trivial observation. NS can occur without variation, because NS is (essentially) the action of environmental factors on an organism. EVOLUTION, on the other hand, cannot occur without variation. EVOLUTION is the end result of natural selection operating on variation within a population. No variation = no evolution. Heritable variation + NS = evolution (ceteris paribus). I think one of the problems in this discussion is that you are continually attempting to decouple the two concepts, and I'm not sure that's a valid way of looking at the question.

I think we may be talking past each other again.

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If you define Natural Selection with variation as is common, then you would tend to ignore the action of environmental factors on an organism. There is no description in the literature of Natural Selection like: Light (environment) falls on the photosynthetic cells of a plant (organism) which contributes to it's reproduction (is selected in). Tend to ignore.

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Since natural selection IS the action of environmental factors on an organism, it would be hard to ignore. I agree with you that there is no description of natural selection as you posted, because what you posted isn't natural selection. When light falls on the chloroplasts of a plant, it's simply light falling on the chloroplasts of a plant - not natural selection, because there's no "selection" occurring. Where NS comes in is when, for instance, you have a plant that is adapted for a certain light level (level being an environmental factor), and the average light level changes. IF the change in light level effects the survival (or reproductive chance if you prefer) of the plant, that effect is "natural selection". If the effect is adverse, the plant might die. In this case, we say the individual plant - or better said the suite of traits that make up the phenotype of that individual plant - was "selected against". With me so far?Note that up to now we haven't even mentioned variation. If ALL of the plants in a particular population are exactly like (no variation) our hypothetical plant above and the average light level changes with adverse effect, what do you think will happen to the population? Since the population is made up of identical individuals, what effects one will effect them all. Hence in this case, the entire population may go extinct.So let's introduce a simple variance - one "type" of this species is as described above (call it type A), another has a slight mutation in its chloroplasts that allows it to more efficiently process available light (call this one type B). Since they're all the same species living in the exact same spot, there's been no real advantage for one type or the other and up to now they've all been living quite happily side by side. Just that A and B are different varieties of the same plant. Some individuals are type A, some individuals are type B. Now let's change the environment (light level). We already know that type A doesn't do well in (say) low-light conditions. Just like our single type above, type A gets selected against and dies out, leaving type B all by itself. This is the most simplistic form of evolution - the change in the average frequency of alleles (types) in a population. A is gone, B is still there, evolution has occurred (in a very simple form). The mechanism that wiped out A is termed natural selection, the result of the mechanism is termed evolution.Hope this helps rather than confusing things further.

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That can't be right. There are many both positive and negative factors which need not change for them to be called selective factors. That is the meaningful knowledge arrived at here, to view an organism's relation to the environment in regards to the event of it's reproduction.

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Well, it IS correct, at least in the simplified example I used. However, the selection pressures on a REAL organism are - as you noted - incredibly complex. A population of organisms without variation that is adapted to its environment (the sum of all selection pressures involved - whether living things or abiotic factors), will be fine unless something changes. Whether that change is introduction of a new pathogen, climate change, a new predator, an invasive species, a new parasite, habitat fragmentation, ecosystem decay, etc, without variation that population is in trouble. WITH variation, there may be individuals within that population that are more likely to survive/reproduce than other members of the population given the change. Sooner or later, by sheer mathematics, the variant alleles that allowed the "better chance" will come to dominate in the population and a new equilibrium will be reached. The variation could even be simply related to our slightly-more-capable plant B slowly supplanting the slightly-less-capable plant A, simply because it's marginally more efficient at processing light at all levels (remember that "environment" includes all the other members of the same population competing for the same resources).