Does Neo-Darwinian evolution require change ?

I used to think this was possible, but lately I have been questioning this. Now I understand we can imagine a scenario where not only the selective pressures don't change, but where the mutations flies back and forth (either through selection or genetic drift) between the same mutations, always reverting back to what it was before.But can such a situation happen in reality ? I don't think so for the following reasons:- Selective pressures always seem to change. Even when the environment in an ecosystem does not change, some species will change and this will impact the pressures on the other species.- Mutation rates per individual per generation are high. Every generation, there is a flood of new mutations coming into the population. Cost of selection obviously limits natural selection from ever keeping up with all these new mutations. Add to that the fact that the majority of mutations have very small effects and so, if they ever reach fixation, it will be through random genetic drift. Which makes it extremely improbable that any species will just have fixed mutations who revert back to the previous mutation, etc.Now if some things are disputed and/or unclear (which I'm sure some are) go ahead and ask a clarification or tell me what is wrong. Just make sure that the point you are raising hasn't already being raised.

Selection in a population cannot be done overwhelmingly in a population without driving the species to extinction. The cost of selection is what puts the upper limit on how much selection can happen in any given generation.A high mutation rate means you would need more intense selection if you want to keep 'in check' all these new incoming mutations (with the majority being harmful). What I am saying is that such high level of selection is impossible because of the cost of selection See following reply to Dr.A Google is your friend. When I say Neo-Darwinian evolution, I mean Neo-Darwinian evolution and I expect that someone with 18k posts on a forum about evolution would know what it is.Neo-Darwinism - WikipediaSimply put, it refers to the mechanism of mutations+NS

This is what I'm asking: given what we know of genetics, and what we know of selection, if we observe any given species (even in an unchanging environment), will we automatically observe macro-evolution if we stay long enough (except in maybe some very statistical rare cases)PS I never liked the terms macro and micro evolution. It brings up two issues. First, living fossils, where a species appears in the fossil record millions of years ago, dissapears, and is found alive and almost identical today.Second, one of the two great trends in the fossil record, according to Gould, is stasis (the other being the sudden appearance of new species). Meaning that once species appear in the fossil record, they remina largely unchanged until they dissapear.So what I'm asking is: Is this even possible if Neo-Darwinism is the mechanism of evolution ?

Extinction arose when the selective pressures became extremely high, ie they went way over the limitation of the cost of selection and it drove the species to extinction.But certainly, you are not proposing that this is 'normal' in the existence of a species. A species that selective pressures are pushing towards extinction is certainly not evolving, it is at the end of the road. (Even if the selective pressures stop for whatever reason, there is still a chance that species will undergo genetic meltdown because of a lack of genetic diversity)This is why I am talking about the period in the existence of a species, where selective pressures where normal, and it's the whole point: during that period, can it even stay in stasis ? With all due respect to dr. Mayr, even if the term had a given definition back in 1895, does not mean that definition hasn't changed with time. The wiki quote you provided certainly shows this when it says that

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Despite this, publications such as the Encyclopaedia Britannica, use this term to refer to current evolutionary theory. This term is also used in the scientific literature, with the academic publishers Blackwell Publishing referring to "neo-Darwinism as practised today", and some figures in the study of evolution like Richard Dawkins and Stephen Jay Gould, using the term in their writings and lectures.

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I understand that ''Neo-Darwinian evolution'' is globally understood within the scientific community to describe the modern synthesis.Edited by slevesque, : No reason given.

I think we both know that, when a fossil is discovered, a tag isn't on it indicating what species, family etc. it belongs to.These are tags put on by the paleontologist, and although I don't doubt this is all done in good faith, I feel that sometimes the slightest of differences can justify giving it a different classification. And even sometimes, even if it is the same, it is given a different name because it isn't in the same period.This is why what is really of interest is not the name given, but the actual differences between the fossil and live representatives. These are, in the case of the Coelacanth and the other living fossils, small and for all intents and purposes, when you consider the time scales involved, you can say that they remained pretty much static. I don't see how this contradicts what I said, seems a bit of a red herring to me.Abrupt appearance of species and prolonged stasis until it's dissapearance from the fossil record are two of the great trends in the fossil record according to Gould. I'm not saying he doesn't believe in evolution, but his ponctuated equilibrium theory clearly requires that species can be static for extended periods of time.

And this has an effect how ? Unless I'm missing something, the structure of DNA has no effect on Mendelian genetics. And although I don't doubt some things were probably added along the way, the core of both mechanism of evolution (selection and genetics) has remained largely unchanged since the modern synthesis.Vocal evolutionists such as Dawkins certainly feel this way and use modern synthesis and Neo-Darwinian evolution to refer to our present day theory of evolution If it is as common as Gould and Eldridge say it a side issue, the point is that it certainly is present in a non-negligeable amount. This solves very little in my opinion, as I don't think given the high mutation rates a static environment is enough to keep any species from gradualistic evolution.An unchanging environment is certainly necessary for stasis, but doesn't seem sufficient. In fact, I have the feeling that any mutation rate above the critical 1 mutation per individual per generation is sufficient to make stasis an extremely improbable outcome.Take for example a species which as a mutation rate of 50mpipg. It means that each offspring will have on average 50 mutations from their parents, and so forht each generation. In fact, even given a generation time of 25 years, this still amounts to about 2,5 million mutations after 1 million years, in any given lineage. In any given lineage means regardless of the environment, regardless of selective pressures, regardless of any outside factors.Now, the questions are:- How much mutations are needed on average to start producing a morphological change ? (this is a bit like rusting atoms on a car, since the vast majority of mutations are near neutral, how much atoms need to rust before we can observe that the car is rusting ?)- What mechanism could potentially lower the number of accumulated mutations down to the number in the first question ? (I would guess genetic recombination would be one) You could develop on this since right now it's an assertion. But I'm certainly not closed on the idea. (although it would fit right in the counter-intuitve science thread)

Yeah well, with conservative numbers and a species with a long generation time, I guess you could fall into the ballpark of acceptable.But 50 Mpipg was very conservative. First off, you have assumed all these mutations were point mutation, affecting only one base pair in the genome. This is not necessarily true. Also, 50 is a very small number, Sanford in his ''genetic entropy'' book cited a recent study which had point mutations only to have a lower estimate of 300 (max 600. in humans). Add unto that insertions, deletions, inversions and you could probably get two ten-fold the number we used here. (actually, I think he got the 300 lower estimate from personnal correspondance)PS And yeah, 2M not 2,5M. That what happens when you calculate at 4h in the morning

The I guess I could formulate it this way: Given the high mutation rates, how can morphological drift NOT happen ?If every single offspring will have 1 mutation or more, and usually much much more, how can the species even stay at that local optimum ? Won't it be 'forced' to drift away from it by the high mutation rate ? I guess natural selection would slow down this drift (meaning the drift isn't morphologically neutral), but I can't see how it could ever bring it to a stop.

I know the basics of Ponctuated equilibrium, and I don't see how all you said about it affects what I'm talking about. Except maybe this piece: But unless you are saying that Gould gives a definition to ''stasis'' that is completely foreign to me, in which said definition allows for significant morphological changes to still be described as stasis, then even this part is irrelevant.

I know it seems tempting to ascribe the term evolution to every single step in a species life, but I think ultimately it is fudging the factors.A species being driven to extinction is experiencing extinction. You can't be saying that it is gaining any novel features, you can't say it in way of becoming another species, you can't even say it is experiencing a change in the frequency of an allele in the population. When selective pressures are at such a high level, all this breaks down and I can't see how any definition of evolution could encompass such a situation.

I understand all these, but I don't see how it answers what I'm asking. Which is that given the high mutation rates, how can it stay at that optimal peak when every single offspring will have inherited so many mutation (the majority deleterious, most only very slightly). Whichever one natural selection ''chooses'', it will still be less fit then it's parents were.As I said, any mutation rate over 1pipg seems to be forcing the population from the optimal peak, with natural selection slowing down the drift but unable to stop it. In fact I have difficulty imagining how any species could sustain the mutational burdain of such high rates.

The scenario I have built does not lead to extinction since I haven't defined any deleterious-to-beneficial ratio of the mutations. All I am interested right now is: how is stasis possible ? How can it not always be continuous change, given the high mutation rates ?This does not yet lead to extinction, since a good enough ratio would simply mean this is evolution.But I'll answer your question still: Since I do think the ratio is not so good, and that the high mutation rates should be leading all species towards extinction, and that this fits right in with my YEC position.

Cost of selection puts a limit on what natural selection can do because it tells us that selection has a cost, you cannot select Ad Infinitum. If, in a given species in a given generation, 5000 individuals can be killed by selection and still maintain the population size stable, then that is the maximum ''cost'' you can pay in that generation to filter the deleterious mutations.Of course this is all probabilities talk, since obviously population size goes up and down. But it cannot for too long downwards, because genetic meltdown is never far away.

What you are fogetting is that we aren't just bacteria, where each generation is a single cell division.Ask yourself, how many cell divisions, each with 75 mutations, happens between the time of the first cell division of a newly fertilized ovum, and the time that cell has become a man and himself procreates. Sanford cites the paper from guy, in which his lower estimate in point mutations is given. Sanford asks by personnal correspondance what his upper estimate was. (And I said between 300 and 600 point mutations, but it may be in fact 100-300 my memory is failing me) I'll try finding the rates he cites, but since I got my book stolen a year ago it may be hard. In any case, Sanford does not pull numbers out of a hat. They are all taking the peer-reviewed litterature.

I understand what your saying, but it is besides the point.The question I am asking is: Is stasis possible ?To answer this we can ask another question: In what situation would stasis be the likely to happen ?And the answer to that seems to be: When a species reaches an optimal fitness peak, and when selection pressures stay constant (he peak does not move). If stasis is in any way possible, this is our best bet to where it could happen.And then I'm saying, won't the high mutation rate force it away from that peak ?Now what you said in your post seems to be that their is potential for change. Peaks are actually saddle points, fitness landscape changes over time, they can jump to a nearby peak. All these factors are potential for change, and in fact makes stasis even more impossible, since if in my 'ideal situation' case selection will at least always fight against change and for stasis, if we take into account what you added selection will at least some times work against stasis, and for change.