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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