Does Neo-Darwinian evolution require change ?

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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.

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I think it's time you supported your claims. Please produce evidence that humans have a mutation rate of at least 50 mutations per individual per generation and that the majority are at least slightly detrimental.

1. Mutational accumulation in offspring is statistical, you cannot say the average is 5, therefore every offspring will be worse.
2. Recombination, anyone?
3. Compensating mutations, anyone?

One of the more recent papers on this, that actually directly compared parental and offspring whole genomes, estimated 70 de novo mutations (Roach et al., 2010). This is in fact lower than most previous estimates of human mutation rates so if anything Slevesque's 50 is probably a rather conservative estimate.The second part about the effect of the mutations is much more contentious.TTFN,WK

Your characterization of 50 Mpipg as "very conservative" is incorrect. It's actually pretty close to what is actually measured. The human mutation rate is ~2.5x10^-8 mutations per base pair per generation, and with about 3 billion base pairs in the human genome that comes out to about 75. Your number of 50 is not "very conservative," but is rather right there in the ballpark. This human mutation rate of ~2.5x10^-8 is for *all* types of mutations, not just point mutations, and is right in the ballpark of the mutation rate for all eukaryotic cells. The precise rate is no doubt impossible to calculate precisely and is therefore open to revision, but you shouldn't put too much stock in figures that Sanford says he obtained from "personal correspondence." When someone has evidence that measurements of the eukaryote mutation rate are off by nearly half an order of magnitude then they'll publish a peer reviewed paper, not write a personal letter. It isn't like a mutation rate 6 to 10 times higher than currently thought could easily go unnoticed.Sanford's position is that the Earth is younger than 100,000 years, that there's no common descent, and that mutation rates are so high that genomes are deteriorating too rapidly to have evolved, but the evidence from the real world says otherwise. Why don't you find some evidence that the actual mutation rate is what Sanford claims, and once we have that in hand we can proceed from there?--Percy

It's difficult to visualize a realistic "fitness landscape" over which evolution operates. There's a dimension for every range of variation, an unimaginable number of dimensions. We tend to think of the fitness landscape as three-dimesional, two dimensions of variation that the third of fitness, with a surface with hills and valleys showing the fitness of each combination of variation. THis is misleading in one importatn way. In the three-dimensional visualization, there are peaks from which it's impossible to go uphill and valleys from which it's impossible to go downhill.In the real multi-dimensional case, many "peaks" are the higher-dimensional equivalent of saddle points. That is, an organism may be as fit as possible considering variation of one characteristic but ther may be higher fitness possible by varying some other characteristic.Another factor is that the fitness landscape changes with time. Even in our three-dimensional visualization, peaks and valleys move so that what was optimum yesterday may no longer be optimum tomorrow.Finally, the peak may be local. There is often a nearby peak of higher fitness, and a sufficiently large jump can cross the vally between peaks.

Let me try to answer this with a visualization in the mind.First this optimal peak is an idealization which few, if any, individuals possess. It is the distillation of many thousands of optimals for all the various attributes that lead to evolutionary fitness (reproductive success). Think visual acuity, number of olfactory sensors, leg muscle strength, hemoglobin efficiency, and literally thousands of other attributes all combined in one ideal value.Imagine a graph. Do not be concerned with the axes values, just see the graph. On this graph you draw this optimal vertical line. This is the line that represents the optimal value of all the attributes combined and is the maximum for reproductive success. Now impose the population bell curve for any specific attribute. Populations being what they are, the apex of the curve will be just off the optimum. Some of the population will have visual acuity less then others, some more and the average (apex) value of the curve will not be on the optimal line. The energy costs of better acuity may make it sub-optimal for this specific species in this environment so better acuity may not translate directly to increased fitness. Remember that fitness does not mean bigger, meaner, stronger. It means having more babies.Now draw the thousands of other bell curves on the graph for all the other attributes necessary for reproductive fitness.For each succeeding generation you must redraw each attribute's bell curve since population values at each point on the curve change. My son will have visual acuity up or down slope from me and my daughter may be on the opposite slope altogether. This is due to the different alleles present, mutations and any other mechanism of genetic change. This new curve for visual acuity will shift slightly from the past generation curve. All the curves will shift with each generation.In aggregate, those individuals closer to the optimum for each attribute will have greater reproductive success which will keep the graphs of succeeding generations from straying too far off the optimal reproductive values.What you end up with is, over many generations, these bell curves dance and wobble around this optimal line.The optimal line will also shift in response to changes in the environment. If this optimal line around which all these attribute curves are dancing shifts slowly enough because the environment is relatively stable over geologic timescales then this is a population in stasis.Stasis is not a period of no change either in the individual attributes' population curves or the central optimal line, but change slow enough to appear somewhat stable over geologic time frames.The punctuated part of PE is when there is a radical shift in the environment which forces a radical shift in the central reproductive optimal line. And a radical shift in the environment also establishes new separate optimal lines on the chart (opens up new ecological niches).Leave catastrophism out as a separate issue altogether.The ancestor population will split with new sets of bell curves dancing and wobbling around each of the various optimal lines established for the changed environment and the opening of new niches. Speciation events have occurred.What we see in the fossil record is an instantaneous arising of new species. The fossil record is dictated by geologic timescales when in fact the new species were established by the usual slow gradual evolutionary processes over thousands of generations over hundreds of thousands of years. Remember that 50,000 generations taking a million years to happen is instantaneous in geologic terms and the fossil record.Punctuated Equilibrium embraces evolutionary gradualism at it's core. What was new and radical about it was the recognition of long periods (geologic time) of populations in stasis versus the view of constant gradualism that came before it.As long as the environment remains somewhat stable, the reproductive optimal line will not move too far too fast. It may slowly shift slightly one way or the other for a few hundred generations then slowly shift back for a few hundred more all in response to minor changes in the environment. On geologic timescales, in the fossil record, it appears to not move at all. No speciation events can be noted.Mutation rates will affect the movement of the population curves around the reproductive optimal line and natural selection, in affecting reproductive success, will keep the curves from getting too far off the reproductive optimal center.Edited by AZPaul3, : No reason given.Edited by AZPaul3, : No reason given.

This is a great point and I linked a few months back to a post from the Pleiotropy blog which had a video showing this in a static fitness landscape and which emphasised that deleterious mutations can in fact be enabling mutations making the jumping or tunelling between local optima more likely.TTFN,WK

However, if I understand correctly this measures the whole genome, most of which appears to have no function. If I am correct, a large majority of these mutations will be truly neutral having absolutely no effect whatsoever. Slevesque's argument requires the majority to be detrimental, so he needs to use the far smaller number of mutations within functional regions of DNA (genes, regulatory sequences and the like).

So learn some imperative programming language such as C or Pascal and then you can do it yourself. You can take a set of assumptions about evolution and see how they work out. I can do that and set the program to find out what happens on average in 10000 cases over 10000 generations and get a result back while I'm slicing up the vegetables for dinner. Computers are really quite fast nowadays.Do it yourself. See what happens.I have.

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 do you mean by stasis? Are you saying that there is no genetic change? Are there any such examples?

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

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.

Ok, so what size population might be limited to 5000 deaths a generation? What kind of organism are we talking about here?Let's take a typical mammal, which have very low fecundity by most standards, let's say a cat. A cat has 3-5 kittens in the average litter. An adult female produces can produce 2 (or more) litters a year. So let's conservatively suppose that a typical female that breeds at all, breeds 4 times, for a total of 16 kittens on average.The male is likely to vary, but each kitten has one father and one mother, so we know that if the population stays steady only two of these kittens must survive to the next generation. That means just 1 in 8 or 12.5% of kittens survive. So your 5000 that can be killed per generation while maintaining a stable population suggests a population size of just 625.That's a very small population, using conservative numbers on the number that can be killed. Consider a frog, a turtle or a bacterium and you can easily see that the number that can be killed per generation outnumber the actual population size by many orders of magnitude.Edited by Mr Jack, : subtitle

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.