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.

Thread copied here from the Does Neo-Darwinian evolution require change ? thread in the Proposed New Topics forum.

You can have all of the elements of a public education system without students who learn, but the thing is that would be unlikely. The theory of evolution is the theory that encompasses the processes that explain the changes that have happened historically and continues to happen. The same processes can occur without large-scale changes that typify evolution, though I wouldn't prefer to call it "evolution."

Huh? Huh?Why?And even if true, so what?Further, what does the topic title even mean? What exactly is "NeoDarwinian evolution"? What was "Neo-Darwinian evolution" then years ago? How about a quarter century ago?Theories get changed whenever new information becomes available. That is why Theories are so strong and powerful.

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Anyone so limited that they can only spell a word one way is severely handicapped!

Something like what you're describing has been observed in "Darwin's finches", where the average phenotype tracks the climate. But this does not (common sense would suggest) involve the alternate fixation of new mutations, just a shift in the frequency of existing alleles.Something more like what you're talking about can be seen in antibiotic-dependent bacteria. I understand that if you take their antibiotics away, it is usually (but not invariably) the case that some bacterium will revert to being merely tolerant of the antibiotic, resulting in the survival of the population. In this case we are talking about mutations becoming fixed, and obviously this could happen several times in a row if you kept on jerking the bacteria around.Of course there's no particular reason why anything which at the same time is fixed by drift should also revert, so the whole genotype needn't get back to exactly where you started.--- I'm not sure where this is going.

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 ?

HUH?Almost every species that ever existed has gone extinct. Huh?Again, so what? Almost every species that ever existed has gone extinct. From your own cites?

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Following the development, from about 1937 to 1950, of the modern evolutionary synthesis, now generally referred to as the synthetic view of evolution or the modern synthesis, the term neo-Darwinian is often used to refer to contemporary evolutionary theory.[7] However, such usage has been described by some as incorrect; with Ernst Mayr writing in 1984:

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"...the term neo-Darwinism for the synthetic theory is wrong, because the term neo-Darwinism was coined by Romanes in 1895 as a designation of Weismann's theory."'

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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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Neo-Darwinian evolution is a century old term and guess what, it is no longer way back then. We have learned much, particularly in the last half century or so, and the Theory of Evolution itself has evolved since then.Edited by jar, : appalin spallin

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Anyone so limited that they can only spell a word one way is severely handicapped!

I think if you check into this you will find that these examples of living fossils are not the same species as the original fossils. For example, the fossil record for Coelacanth includes eight families of extinct critters and one family that is mostly extinct (six separate genera are extinct). A single new genus within that family has two separate species, both attributed to modern specimens. All in all, about 25 genera and a whole lot of species of Coelacanth are extinct, and one genus and two species are still holding on. The modern ones are not even in the same genus as the others, and most aren't even in the same family. See the Wiki articleThis is not an accurate description of Gould's position. Species remain largely unchanged for long periods of time when there is little change in their environment. When their environment changes they either adapt to it or go extinct. The faster the environment changes the more pressure there is for species to change, and the greater chance for either 1) change that we later classify as a new species, or 2) extinction. (Lots of species have "disappeared" by changing to a new species.)As your examples are incorrect, this is moot.

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Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.

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.

In which case: why do we care? The modern synthesis predates such cutting edge discoveries as the structure of DNA.In a bit more answer to your question: evolutionary theory can cope just fine with stasis (which is much less common than Gould and Eldridge's incorrect punctuated equilibrium hypothesis would have us believe). Habitat tracking is a major part of the explanation, though, so the actual environmental change experienced by an organism is much less than that apparent in the environment as a whole.Also, if you compare apparently morphologically static organisms using genetic techniques you find that there's just as much change going on as in morphologically divergent organisms.Edited by Mr Jack, : Typo: habitat tracking, not habit tracking

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)

Avise et al (1994) 'A Speciational History of "Living Fossils": Molecular Evolutionary Patterns in Horseshoe Crabs' Evolution Vol. 48, No. 6 (Dec., 1994), pp. 1986-2001

Sounds like you're talking about people, who have about 3 billion base pairs. A mutation rate of 50 mutations per individual per generation is 1.66*10^-8. That's pretty small. Even after a million years of 25-year generations in a single lineage (which is 2 million mutations, not 2.5) that's only 0.07% of the entire genome. 99.93% of the genome is unchanged.There are various measures of the degree of similarity of the human and chimp genomes, but let's say they're 97% similar after the 7 million years that have passed since the lineages separated. That's less than the 99.53% we would obtain using your numbers for a single lineage for 7 million years of a just a million. The lower similarity of 97% for chimps and humans is because mutations are contributed by all individuals in a population, and they become combined and selected (for and against) in subsequent generations.I think the numbers you've used are acceptably ballpark and fairly consistent with observations.--PercyEdited by Percy, : Grammar.