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Author | Topic: The End of Evolution By Means of Natural Selection | |||||||||||||||||||||||||||||||||
Faith  Suspended Member (Idle past 1704 days) Posts: 35298 From: Nevada, USA Joined: |
Just read through this discussion of budgie breeds.
http://www.bestofbreeds.net/al-nasser/article9.htm Mutation is assumed in a couple of instances but mostly it's a complicated discussion of how you get different traits from combinations of dominants and recessives. Without grasping all the particulars, I'd say this suggests that in the wild if birds migrate away from a parent population to set up new populations you could easily get many new types of bird populations just from the built-in alleles. This is the sort of thing I was thinking of for examples like the greenish warblers RAZD brought up. Many possible combinations means any random selection force such as geographic isolation would bring out all kinds of new expressions. So should we say the new traits had been previously "hidden" or what? If the new population stays reproductively isolated then there's no reason their own peculiar characteristics couldn't become fixed and come to define a new species, thanks to mere isolation of a portion of a population from the parent population, a form of random selection. This has to be a process of genetic reduction not addition simply because the migration has taken a small number out of a large number to get the new effect. And yes, again, you could still have enough diversity for further population splits with the creation of yet new varieties. But the trend is always to reduction. Any given path of variation -- any particular bird variety -- has to have an end point beyond which further variation can't happen. It's the perfect expression of its particular complement of alleles and there aren't any "extras" left as it were, for making new varieties. I guess I'm repeating myself again. Seems so clear to me. Edited by Faith, : No reason given. Edited by Faith, : No reason given. Edited by Faith, : No reason given.
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Dr Adequate Member Posts: 16113 Joined:
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Seems so clear to me. When everything else you say seems to be a dirty muddle of obfuscation and lies. I wonder if the (as you see it) blinding clarity of your conclusion and the (as everyone else sees it) filthy mess of your arguments could be related in some way? Edited by Dr Adequate, : No reason given.
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Faith  Suspended Member (Idle past 1704 days) Posts: 35298 From: Nevada, USA Joined: |
Catching up on some earlier posts.
Assume a population has 26 genes labeled a-z. Further assume that each gene has 4 alleles labeled a1-a4, b1-b4, and so forth. An earthquake occurs that causes a river to change course, and a subpopulation becomes trapped on land that is now an island. This population only has the first two alleles of each gene, a1-a2, b1-b2, and so forth. If this alone were sufficient for speciation, then you should be able to list a combination of specific alleles that could form in the subpopulation but not in the main population. OK, that's an interesting way to lay it out, but immediate speciation isn't required by my model. I think I can easily enough list a combination for the subpopulation, at least, that should demonstrate how it can get a dramatic difference in phenotypes by taking some and leaving others behind: Let a daughter population be formed from individuals carrying anywhere from 1% to 40% of a-1 &3, b-1, c-4 (a single allele would have to come from individuals homozygous for this trait), d-1 & 2, e-2, f-3& 4, g-1&4, h-1,2,3&4, i-1, 2, 3& 4, j-3, k-4, l-2,3, m-1,4 and so on randomly through z, plus maybe 90% of, oh, m-4. That is, SOME of the alleles are taken from the parent population, only 1 for some of the genes, but up to all 4 for others, and if the daughter population is very much smaller it may not deprive the parent population of a single allele so it will go on with more or less its usual gene frequencies. The daughter population, however, is going to have a completely different mix and will develop a different appearance for that reason. And since it's smaller and it's left more alleles behind than it took it's clearly in a condition of reduced genetic diversity compared to the parent population. But I've never claimed that such a situation would lead to speciation. I take speciation to be usually the end product of many selection processes, although I do recognize that reproductive isolation can occur long before variability has run out.
How are you going to do that, given that every allele in the subpopulation exists in the main population? For example, try this one: a1b2c1d2e1f2g1h2i1j2k1l2m1n2o1p2q1r2s1t2u1v2w1x2y1z2There's not a single allele in that list that doesn't exist in the main population. No matter how you mix and match alleles in this subpopulation, it is impossible to come up with a combination that couldn't happen in the main population. Well, if the population is not extremely large you could sharply reduce the number of alleles for any given gene by their being taken with the migrating subpopulation, say along with the 90% of m-4 also 80% of n-1, 70% of o-2 & 90% of p-3, and 100% of q-3 and r-2. The high percentages gone would at least make some combinations far less likely though not impossible, but missing 100% of all the individuals that possess a particular allele will make combinations with that one definitely impossible.
That's why allele reduction does not result in speciation. Eventually it will as the processes that select and isolate continue to work. Speciation is brought about by various forms of population splitting, generally a smaller part of a parent population becoming a daughter population, according to many sources I've found, as shown in this little chart at Wikipedia: File:Speciation modes.svg - Wikipedia The smaller populations are formed through different circumstances but their composition is the same in all cases -- made up of a portion of the alleles of the parent population. Edited by Faith, : No reason given.
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nwr Member Posts: 6484 From: Geneva, Illinois Joined: Member Rating: 9.2 |
Faith writes:
The fact that mutation is only mentioned a few times does not show that there were not other mutations. The breeders would be mainly concerned with mutations with visible traits that might be attractive to bird owners. They would not notice mutations that did not cause visible changes.
Mutation is assumed in a couple of instances but mostly it's a complicated discussion of how you get different traits from combinations of dominants and recessives. Faith writes:
Yes, but they wouldn't be considered a separate species unless there were further divergence from the original group. Maybe a mutation allows them to feed on a tougher seed than before, and because that tougher seed is abundant in the new environment you get strong selection pressure to favor the new mutation.
Without grasping all the particulars, I'd say this suggests that in the wild if birds migrate away from a parent population to set up new populations you could easily get many new types of bird populations just from the built-in alleles.
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Admin Director Posts: 13108 From: EvC Forum Joined: |
For the message this is a reply to. See you tomorrow.
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Percy Member Posts: 22954 From: New Hampshire Joined: Member Rating: 7.1 |
The scenario you describe, where both parent and daughter populations lose alleles through many generations such that the parent population comes to have alleles the daughter population does not have, and the daughter population comes to have alleles the parent population does not have, seems like it could produce speciation if it ever really happened.
But the differences between the parent and daughter populations with regard to which alleles they possess is also heavily influenced by mutation. Whether you believe in beneficial mutations or not, every offspring has mutations that result in a unique allele or two (a reasonable average figure that's in the ballpark) not seen before in the species. Consider the population of rabbits in Australia (a population of millions and millions of rabbits). Each year millions and millions of baby rabbits are produced, and each one has on average one new allele. This means that each generation of rabbits gets millions and millions of new alleles. Given that reproduction is almost never perfect, this is inevitable. It isn't a case of whether it happens. It's a case of how you would ever stop it. --Percy
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Faith  Suspended Member (Idle past 1704 days) Posts: 35298 From: Nevada, USA Joined: |
Mutation is assumed in a couple of instances but mostly it's a complicated discussion of how you get different traits from combinations of dominants and recessives. The fact that mutation is only mentioned a few times does not show that there were not other mutations. The breeders would be mainly concerned with mutations with visible traits that might be attractive to bird owners. They would not notice mutations that did not cause visible changes. I don't think it affects my point if there are other mutations since they act like the alleles I'm talking about in any case.
Faith writes: Without grasping all the particulars, I'd say this suggests that in the wild if birds migrate away from a parent population to set up new populations you could easily get many new types of bird populations just from the built-in alleles. Yes, but they wouldn't be considered a separate species unless there were further divergence from the original group. Seems to me 1) this process produces some very striking divergence and 2) descriptions of new species don't make them sound like much more than the same species with some striking new characteristics. Incredible Batch of Rare and New Species Discovered - Science and Nature LiveJournal http://animal.discovery.com/...images/red-eyed-tree-frog.jpg Built-in alleles in new combinations thanks to isolations of part of the gene pool explain it fine I think. But it doesn't really change anything in my model here to assume they are mutations either.
Maybe a mutation allows them to feed on a tougher seed than before, and because that tougher seed is abundant in the new environment you get strong selection pressure to favor the new mutation. OK, you want to insist on mutations, though the descriptions could just as well apply to new combinations of built-in alleles as to mutations so I see no need for mutations -- AND the mutations are as usual assumed and not known for a fact to be the source of any given novelty -- but for my purposes I don't really think it matters because the processes that select and isolate and reduce genetic diversity will operate on both just the same.
Faith writes: Mutation is assumed in a couple of instances but mostly it's a complicated discussion of how you get different traits from combinations of dominants and recessives. The fact that mutation is only mentioned a few times does not show that there were not other mutations. True, but my mention of their reference to mutation was only in passing and what's interesting to me about that article is the complicated changes that different combinations of dominants and recessives can produce, which even in the wild with population splits could produce quite a range of new varieties. Again, it is apparent that whenever mutations are invoked it is an assumption that usually isn't proved. A new trait emerges, it's called a mutation, it's assumed. Sometimes the gene can be pinpointed and the change accounted for as a mutation, but the theory that all alleles come from such changes isn't proved by that, still merely assumed. If mutations happen to be occurring more frequently now than in the past, and they are accidents or mistakes that sometimes produce something neutral that can be regarded as desirable, such as by breeders, but couldn't have produced all alleles, how could this be known? The changes all occur on a strand of alternating chemicals, so by chance sometimes a useful combination could result even by accident, but if that's all there is to mutations seems most probable that the disease-producing mutations would have wiped out all living things long before anything functional could come up. But I didn't want to stay in the conversation about mutations right now. Even if they do occur and account for the material for variation (really, I nearly choke saying that because I'm so convinced it doesn't happen except possibly very rarely) but even if they do, the processes of selection and isolation that bring out new characteristics for new populations still reduce the genetic diversity in producing these new varieties no matter what its original source. ===========I don't know what happened in this post. It appears that your post got duplicated and I answered parts of it twice. But I don't think I'm too terribly repetitive and it would be very hard to rewrite it so I'll just leave it.
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Faith  Suspended Member (Idle past 1704 days) Posts: 35298 From: Nevada, USA Joined: |
The scenario you describe, where both parent and daughter populations lose alleles through many generations such that the parent population comes to have alleles the daughter population does not have, and the daughter population comes to have alleles the parent population does not have, seems like it could produce speciation if it ever really happened. Seems to me that if only the daughter population changes it would also lead to speciation. And I don't see why it couldn't happen since it is produced by a simple migration of a small portion of a population away from the rest, and it does fit that little diagram from Wikipedia that I posted showing the different types of speciation.
But the differences between the parent and daughter populations with regard to which alleles they possess is also heavily influenced by mutation. Whether you believe in beneficial mutations or not, every offspring has mutations that result in a unique allele or two (a reasonable average figure that's in the ballpark) not seen before in the species. It doesn't change the processes I'm trying to focus on if you want to assume that. Even if the changes are produced by mutations it still takes the selecting and isolating to bring them out and form a new characteristic phenotype for a new population. Such mutations could simply stay in the population without such processes operating but that wouldn't produce a new variation or species, simply a population with high variability.
Consider the population of rabbits in Australia (a population of millions and millions of rabbits). Each year millions and millions of baby rabbits are produced, and each one has on average one new allele. This means that each generation of rabbits gets millions and millions of new alleles. Given that reproduction is almost never perfect, this is inevitable. It isn't a case of whether it happens. It's a case of how you would ever stop it. OK, such mutations occur, but as long as you can't tell what those alleles are actually doing, whether they are actually the source of a new variety for instance, they could still best be regarded as a pathological event. But again, assuming they do produce new viable traits, you still have to select and isolate them to get a new variety or species, which reduces the genetic diversity for the new population, and when that happens the majority of the millions are reproductively cut off so that the new population with the new characteristics can emerge -- because of its reduced genetic diversity. Edited by Faith, : No reason given.
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Blue Jay Member (Idle past 2958 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined: |
Hi, Faith.
I had sworn off debating with you on this topic, but I've got to put one little tidbit out here for you to see:
Faith writes: Even if the changes are produced by mutations it still takes the selecting and isolating to bring them out and form a new characteristic phenotype for a new population. Such mutations could simply stay in the population without such processes operating but that wouldn't produce a new variation or species, simply a population with high variability. If such mutations could stay in the population, what is to stop it from being one of the alleles that comes to dominate a daughter population, thereby distinguishing the daughter population from the parent population? Wouldn't this be the addition of a new allele, which then came to dominate a population? And, wouldn't it be working according to the basic process you described in your argument? This is what we are talking about: this is how evolution happens, and this is how mutation changes the entire countenance of your model. Edited by Bluejay, : "your" to "you" -Bluejay (a.k.a. Mantis, Thylacosmilus) Darwin loves you.
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Faith  Suspended Member (Idle past 1704 days) Posts: 35298 From: Nevada, USA Joined: |
I've looked over the answers to my questions about dog breeding a number of times and find them so various there isn't a simple way to respond to them. I wanted to combine them and respond to them as a unit but the opinions are so different that would take more organization than I'm up to. I thought they would help me identify a trend in the answers I've been getting but unfortunately they raise more problems than they solve in that respect. I may yet go through them one by one.
In any event this statement of yours reminded me of that topic.
Yes, but they wouldn't be considered a separate species unless there were further divergence from the original group. There's enormous divergence between dog breeds and yet dogs have such high genetic variability that they never come to form separate species so that the breeds always have to be carefully managed by their breeders to prevent contaminating their select gene pools. Hard to find more divergence than between say a greyhound and a Pekinese, or a Great Dane and a chihuahua and so on. If you want to say mutations account for these differences I'm only going to say as usual that in most cases you don't know that for a fact and merely assume it, but I'm also not going to object beyond that. Because each breed is a small subset of all dogs it has to have much reduced genetic diversity no matter what the original source of its peculiar characteristics. That's my theme song: you don't get diversity of traits without loss of genetic diversity.
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Faith  Suspended Member (Idle past 1704 days) Posts: 35298 From: Nevada, USA Joined: |
Hi, Faith. I had sworn off debating with you on this topic, but I've got to put one little tidbit out here for you to see: Faith writes: Even if the changes are produced by mutations it still takes the selecting and isolating to bring them out and form a new characteristic phenotype for a new population. Such mutations could simply stay in the population without such processes operating but that wouldn't produce a new variation or species, simply a population with high variability. If such mutations could stay in the population, what is to stop it from being one of the alleles that comes to dominate a daughter population, thereby distinguishing the daughter population from the parent population? Nothing at all in principle. If such an event occurred it would follow the same pattern I'm describing. In order for its trait to emerge competing traits would have to be eliminated. Same story as in all the other cases. And that's reduction in genetic diversity, in this case letting a mutated allele come to expression and dominate the new population. It's six of one, half a dozen of the other when it comes to the source of the new trait. You still have to have the selection, the isolation, the reduction in numbers that is how a daughter population is formed at all, and that reduces the genetic diversity at the same time it allows the new trait to come to expression. Sorry, being repetitive again but it seems necessary.
Wouldn't this be the addition of a new allele, which then came to dominate a population? And, wouldn't it be working according to the basic process you described in your argument? Yes it would as I described above before getting to this sentence.
This is what we are talking about: this is how evolution happens, and this is how mutation changes the entire countenance of your model. Even if mutation is the source of a new trait, what I'm talking about is the processes that select and bring new traits to expression, not what produces the allele, and the emergence of a new daughter population with its own peculiar character requires selection and isolation, which always requires reducing genetic diversity. This is what is really going on in this type of change in gene frequencies -- and this is the definition of evolution or one of them -- and if reduced genetic diversity is necessary to the emergence of new traits then evolution has less and less to feed on as new traits emerge until finally it must reach an end point beyond which it can no longer occur at all. Edited by Faith, : No reason given. Edited by Faith, : No reason given. Edited by Faith, : No reason given. Edited by Faith, : No reason given.
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nwr Member Posts: 6484 From: Geneva, Illinois Joined: Member Rating: 9.2 |
Faith writes:
There is a big difference between natural selection and artificial selection.Seems to me 1) this process produces some very striking divergence and 2) descriptions of new species don't make them sound like much more than the same species with some striking new characteristics. With artificial selection, the breeders are usually attempting to emphasize the differences, and to make them more pronounced. This leads to creatures with widely different traits but only small genetic differences. With natural selection, the tendency is for the unusual traits to be blended back into the population. So you mostly only see noticeably different characteristics when there are rather larger genetic differences.
Faith writes:
These days they are doing quite a bit of DNA sequencing, and measuring the genetic differences between species. If somebody were to discover two separate species where the only genetic differences were that one of the species had lost some of the alleles of the other, that would likely make big news. Possibly it would also lead to reconsideration of whether those are really parts of the same species.OK, you want to insist on mutations, though the descriptions could just as well apply to new combinations of built-in alleles as to mutations so I see no need for mutations -- AND the mutations are as usual assumed and not known for a fact to be the source of any given novelty -- but for my purposes I don't really think it matters because the processes that select and isolate and reduce genetic diversity will operate on both just the same. I am not a biologist (I'm a mathematician and computer scientist). But it sure seems to me that the experimental evidence is indicating that there are mutations involved in the formation of species. That said, the species classification is a bit arbitrary and sometime revised on new information.
Faith writes:
It isn't just assumed. Sure, sometime new species are defined without checking the DNA. However, when checks are later made, they seem to show that there were indeed mutations. Presumably biologists have a pretty good eye for recognizing this, though sometime classifications are changed.Again, it is apparent that whenever mutations are invoked it is an assumption that usually isn't proved. A new trait emerges, it's called a mutation, it's assumed. Sometimes the gene can be pinpointed and the change accounted for as a mutation, but the theory that all alleles come from such changes isn't proved by that, still merely assumed. Keep in mind that it isn't that there is a new mutation, and a new species springs up. It's more likely that a new mutation just adds to the genetic diversity of the existing population. Then some other event, perhaps a new predator or a new food source, changes the selection pressures and that divides the population into separate sub-populations which then drift apart. These subpopulations then pick up more genetic diversity with further mutations. It isn't just selection, and it isn't just mutation that gives rise to new species. It is both acting in conjunction with one another.
Faith writes:
I disagree with the frequent description of mutations as mistakes or accidents or copying errors. It seems to me that they should be considered part of how biology works. If somebody were designing a biological system (as a theistic evolutionist might believe), that designer would probably want to design a system that produced random mutations. The "designed" mutation rate would need to be low - too high a rate would cause problems. But it would need to be high enough that there is variety around to allow some of the population to be able to resist unpredicted new diseases or environmental changes or predators.
If mutations happen to be occurring more frequently now than in the past, and they are accidents or mistakes that sometimes produce something neutral that can be regarded as desirable, such as by breeders, but couldn't have produced all alleles, how could this be known? Faith writes:
I don't think there is actually much disagreement with that. Most would agree that selection and isolation can lead to a change in phenotype and a reduction in diversity. Where we disagree with the thesis of your OP, is that we see the diversity being replenished over time, as new mutations accumulate.
But I didn't want to stay in the conversation about mutations right now. Even if they do occur and account for the material for variation (really, I nearly choke saying that because I'm so convinced it doesn't happen except possibly very rarely) but even if they do, the processes of selection and isolation that bring out new characteristics for new populations still reduce the genetic diversity in producing these new varieties no matter what its original source.
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nwr Member Posts: 6484 From: Geneva, Illinois Joined: Member Rating: 9.2 |
Faith writes:
This has a lot to do with the differences between the artificial selection of the breeder, and natural selection that occurs in nature.There's enormous divergence between dog breeds and yet dogs have such high genetic variability that they never come to form separate species so that the breeds always have to be carefully managed by their breeders to prevent contaminating their select gene pools. Hard to find more divergence than between say a greyhound and a Pekinese, or a Great Dane and a chihuahua and so on. If you want to say mutations account for these differences I'm only going to say as usual that in most cases you don't know that for a fact and merely assume it, but I'm also not going to object beyond that. Artificial selection is usually done to emphasize differences in exhibited traits. Thus you can have relatively large differences in characteristics, with only a small amount of genetic difference involved. With natural selection, those kinds of differences in traits tend to blend back into the population and don't make as obvious a difference in the population as a whole. So, by the time you see large differences in traits between natural populations, the genetic differences between those populations are likely to be considerably greater than the genetic differences involved in domestic breeding.
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Percy Member Posts: 22954 From: New Hampshire Joined: Member Rating: 7.1 |
Faith writes: Seems to me that if only the daughter population changes it would also lead to speciation. Since in this case the parent population possesses all alleles of the daughter population, every member of the daughter population can only possess alleles already in the parent population, just as is true for all members of the parent population. There's nothing genetically to distinguish a member of daughter population from the parent population. There isn't a single example in the technical literature of related species where one has a strict allele subset of the other. If reductions in genetic diversity were really a common way speciation happens and if mutations play little or no role then scientists should have long ago discovered tons and tons of examples of this, yet they never do.
OK, such mutations occur, but as long as you can't tell what those alleles are actually doing, whether they are actually the source of a new variety for instance, they could still best be regarded as a pathological event. We're aware that in cases were there's no evidence you assume you're right. If you're into answering old posts, why not answer Message 309. --Percy
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Faith  Suspended Member (Idle past 1704 days) Posts: 35298 From: Nevada, USA Joined: |
There is a big difference between natural selection and artificial selection. With artificial selection, the breeders are usually attempting to emphasize the differences, and to make them more pronounced. This leads to creatures with widely different traits but only small genetic differences. Not getting how this needs "only small genetic differences" Certainly there are differences between artificial and natural selection, but the principle is the same in both. What is selected has to be isolated from what is not selected if new traits are to be expressed and preserved and become part of a new variety.
With natural selection, the tendency is for the unusual traits to be blended back into the population. So you mostly only see noticeably different characteristics when there are rather larger genetic differences. I agree about the tendency for unusual traits to be blended back into the population, but this would be when there is no selection pressure to isolate them, no migration to bring them out, etc.; similarly, I don't see why "larger" genetic differences would be necessary to bring out such traits. What brings them out is what I've been emphasizing -- isolation, selection, protection from competing traits, reduction of genetic diversity.
These days they are doing quite a bit of DNA sequencing, and measuring the genetic differences between species. If somebody were to discover two separate species where the only genetic differences were that one of the species had lost some of the alleles of the other, that would likely make big news. This is what was more or less assumed, though, in principle at least, before mutations became the big mover and shaker. And in principle it should be testable, even in the laboratory: If enough specimens of a small highly variable species could be gathered and allowed to interbreed for a while to build up the population, then you'd take from it a small number to be isolated in a separate holding place and repeat the same process with them. Then do DNA sequencing on as many as possible in both populations. There should be both an apparent new characteristic to the subpopulation AND reduced genetic diversity compared with the first population. You could repeat this same process a number of times, taking a small number from each new population after it has been allowed to grow to reasonable numbers, to allow it to interbreed and develop on its own, and the trend should continue if my claim has anything to it. You would no doubt see traits emerge that you want to call mutations, but the test should be in the reduced genetic diversity that brings them out.
Possibly it would also lead to reconsideration of whether those are really parts of the same species. Good reason to do it in a laboratory if possible.
I am not a biologist (I'm a mathematician and computer scientist). But it sure seems to me that the experimental evidence is indicating that there are mutations involved in the formation of species. OK, most people are convinced of that. I'm one that isn't though.
That said, the species classification is a bit arbitrary and sometime revised on new information. Faith writes: Again, it is apparent that whenever mutations are invoked it is an assumption that usually isn't proved. A new trait emerges, it's called a mutation, it's assumed. Sometimes the gene can be pinpointed and the change accounted for as a mutation, but the theory that all alleles come from such changes isn't proved by that, still merely assumed. It isn't just assumed. New traits are automatically flatly called mutations without evidence. That's assuming. Dr. A SAID that it is assumed that mutations produce alleles. Bluejay argued from a position that tacitly said the same -- "but we have no other source of alleles."
Sure, sometime new species are defined without checking the DNA. However, when checks are later made, they seem to show that there were indeed mutations. Presumably biologists have a pretty good eye for recognizing this, though sometime classifications are changed. Biologists are working under the assumed ToE which depends on mutations. Although I don't doubt the integrity of the scientists, that sort of bias must skew where they look and what they look for.
Keep in mind that it isn't that there is a new mutation, and a new species springs up. It's more likely that a new mutation just adds to the genetic diversity of the existing population. Then some other event, perhaps a new predator or a new food source, changes the selection pressures and that divides the population into separate sub-populations which then drift apart. These subpopulations then pick up more genetic diversity with further mutations. It isn't just selection, and it isn't just mutation that gives rise to new species. It is both acting in conjunction with one another. I address this at the bottom so I'll leave it for now.
Faith writes: If mutations happen to be occurring more frequently now than in the past, and they are accidents or mistakes that sometimes produce something neutral that can be regarded as desirable, such as by breeders, but couldn't have produced all alleles, how could this be known? I disagree with the frequent description of mutations as mistakes or accidents or copying errors. It seems to me that they should be considered part of how biology works. Of course you do, nwr, and of course I don't. We do disagree. I do nevertheless usually assume mutations for the sake of this argument.
If somebody were designing a biological system (as a theistic evolutionist might believe), that designer would probably want to design a system that produced random mutations. It could be, there's nothing in the Bible against it, and I've even mused on the possibility that there could have originally been mutations that did function more or less as evolutionists insist they function, but then they wouldn't have produced so many diseases, so something has drastically changed in the system if so. It's the thousands of known genetic diseases in human beings that belies it to my mind.
The "designed" mutation rate would need to be low - too high a rate would cause problems. But it would need to be high enough that there is variety around to allow some of the population to be able to resist unpredicted new diseases or environmental changes or predators. OK, I'll accept that as a tentative model for a Designer-produced mutation system. But the Biblical God wouldn't design mutations to produce diseases -- that would have to reflect a deterioriation of the system.
Faith writes: But I didn't want to stay in the conversation about mutations right now. Even if they do occur and account for the material for variation (really, I nearly choke saying that because I'm so convinced it doesn't happen except possibly very rarely) but even if they do, the processes of selection and isolation that bring out new characteristics for new populations still reduce the genetic diversity in producing these new varieties no matter what its original source. I don't think there is actually much disagreement with that. Most would agree that selection and isolation can lead to a change in phenotype and a reduction in diversity. Where we disagree with the thesis of your OP, is that we see the diversity being replenished over time, as new mutations accumulate. Yes, that is the main argument here, which I keep trying to answer by saying that it doesn't matter what the source of the variation is. That is, when a new trait undergoes selection and isolation in order to become a characteristic of a new population, the variability is lost, and MUST be lost or the new characteristic will not emerge. It will be blended back instead and lost in the larger population as you mention above. But when selection and isolation occur, that is the usual road to speciation, which is even confirmed by that diagram from Wikipedia I posted earlier:File:Speciation modes.svg - Wikipedia If you add mutations at that point you will only lose your new variety or species as it all blends back together again, same as in your own example above when a new trait emerges in a large population without being selected, or when a bred dog accidentally mates with a mutt. To GET a new variety or species you need the selecting and isolating and that requires reduced genetic diversity. Even if in the end what you get is a mutation-derived set of traits it still only gets expressed as a separate variety or population by these means, and these means ultimately come to an end at least in principle with a highly genetically depleted new variety or species. Let me try to say it this way: What I'm trying to describe isn't a matter of rates of mutation versus rates of selection, it's about what the selection DOES with the mutated traits to bring about new species. A gazelle can probably outrun a lion but the lion might outmaneuver it and eat it at the end of the race anyway. Same in my model. (Sort of). The selection eats the mutation. If mutations are simply the way alleles are produced then reduction and isolation are going to act on them exactly as I've been describing anyway. Edited by Faith, : No reason given. Edited by Faith, : No reason given.
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