Natural Limitation to Evolutionary Processes (2/14/05)

Hi Faith, And it is still subject to the same processes of increases in variability. These rates of variability accumulation are traits like any other, and are selected for like any other trait. That is, if an organism reduces its rate of genetic variability accumulation, (as in the development of "perfect" DNA replicating mechanisms), it may be selected against in times of habitat change, while others of the species with "imperfect" replication may fare better. There will always be instances where available genetic variation is not enough to prevent extinction in response to habitat change. This is not a problem for evolution, though, as you seem to suggest. Natural selection works by causing the death of unfit organisms - sometimes this happens at the species level. Just to be clear here, PaulK said nothing about beneficial variation in his post, he only wrote of increases and decreases in variation. Every new non-lethal variation has the potential to be beneficial, but that is up to selective forces. Individuals with those twenty "adaptive possibilities" will be more successful in the population, because they will have increased fitness. Importantly, this does NOT mean that the other 19,980 organisms in the population are going to immediately die off, causing a drastic reduction in variability. Rather, all of the organisms will continue to try to pass on their genes. The ones with the adaptations will be more successful, and will interbreed with other population members without the adaptations. Variability is NOT lost when a beneficial mutation is selected for in a large population; rather that mutation increases throughout the population, why the diversity of the rest of the genome remains intact.As an example, a mutation appears in a frog that allows it greater fly-catching success. Since this frog is more fit than the rest of the population, he will sire more offspring than other frogs, causing the fly-catching-mutation to spread through the population the frog lives in. However, the spread of the fly-catching-mutation has no effect on the genetic variation contributing to other traits, like predator evasion or the immune system. The genetic variability remains intact.Does that make sense?

Did you know Darwin thought the same thing? But novel mutations do occur in animal husbandry, and breeders select for these mutations despite the fact that they are unpredictable. There's a lot of money and fame to be earned in the world of animals breeding if you are the only person with a particular allele.Check out the Nearly Hairless Club, devoted to hairless guinea pigs, whose hairlessness comes from a mutation that only recently appeared (in I think the last decade or so). Prior to that, the hairless "Baldwin" allele did not exist in any guinea pig population, anywhere. Baldwins have now achieved some measure of popularity, and thus the mutation has been selected for.Are you really arguing that adaptive mutations never occur? If you are interested, there is the thread Beneficial Mutations which you may find interesting.

Hey Faith, I also appreciate that you are willing to learn and keep an open mind. Perhaps, but evolution does NOT only proceed by such drastic events that kill off the majority of the population. I tried to explain this to you on page one of this thread with a frog example, but perhaps you missed it. I'll try again:An individual animal is born with a mutation that makes it slightly better at catching prey, and thus slightly more fit than the rest of the population. This does not mean that the rest of the population will now die off en masse. Instead, the frequency of that mutated allele may increase over generations in the population, since individuals carrying that allele are more fit and thus more likely to have offspring. As the frequency of the mutated allele increases, the frequency of the original alleles for that gene decreases. The mutated allele becomes fixed in the population, replacing previous allelic diversity for that gene with a single allele (a state which I'll call "zero allelic diversity").But here is the important part, that I fear you are missing: Even though the success of the mutated allele drops "diversity" for its gene to zero, the organisms within the population have NOT reduced the allelic diversity for the other 20,000 genes in their genome. Thus, fixation of an allele for one gene generally has neglible effects on the allelic diversity for the other 99.99% of the genome. Genes coding for any other trait the population have retained their allelic diversity.Is that clear?Also - you seem hung up on the bacteria-mutation example, which is a good example because monoculture allows the experiment to begin with zero allelic diversity. However, that is not the only example of documented mutations (I gave you another one - the Baldwin mutation that appeared in a closed population several years ago and results in hairless (and I think darn cute) guinea pigs.)I worked in mouse genetics for several years - mouse geneticists have established "inbred" mice that are homozygous for every gene, which means they have zero allelic diversity, not unlike bacterial monoculture. Mutations occur on a very regular basis in closed populations of these inbred, zero-allelic-diversity-mice. A simple example is an inbred mouse strain that happened to have black fur. One day white-furred mice began appearing in the population, and the mutation that caused this difference was identified. Examination of the DNA of the great-grandparents of the white-furred mice did not reveal the same mutation. There was no source of the white-furred gene except for mutation, since there was zero allelic diversity at that gene in the grandparents of the mice with the mutation.

I don't know the specifics of the examples you gave, so I didn't give a specific answer. Yes. Inbred creatures are more vulnerable to drastic environmental change and extinction.However, like the title of the post says - evolution does not proceed solely by drastic events. In other words, drastic events that result in severe genetic bottlenecks only represent a small portion of evolutionary change. My guess is that most populations that pass through a severe genetic bottleneck go extinct. But again, evolution doesn't proceed only through bottlenecks. See message #43 in this thread. Then you should stop making concrete statements like the following: Again, you are discussing relative rates when you haven't presented the actual rates. Also, evolution theory itself requires some loss of diversity, so ANY loss of diversity does NOT suggest the opposite of the theory.Also, "diversity" is subject to positive selection in most cases. That is, natural selection maintains diversity of some alleles. Yes it is! Evolution does NOT proceed by natural selection judging one gene at a time - an organism's phenotype is the sum of all of its genes, and all of its genes undergo selection. False. Evolution proceeds by mutation and selection, not just selection. In some cases selection reduces diversity; in other cases selection maintains diversity. I'm not sure if the mutation has been mapped to a specific gene in the guinea pig, (though it has been in the mouse mutation I mention.) How do we know it is a mutation? Well, like the curly-eared cats mentioned above, humans in general, and specifically animal breeders, would have noticed a hairless guinea pig or a curly-eared cat in the past few thousand years, especially these mutation, both of which are simple single gene mutations, and NOT the result of complex multi-gene interactions. And the curly-ear mutation is a dominant mutation (all cats with a single copy of the mutation have curly ears), so it would have been seen if it existed prior to 1981. Variation produced by mutation-I'm not sure if you understood the point of the mouse example or not. It is a case where it is absolutely known that mutation increased genetic variation. Offspring had an allele that their grandparents did not have. The mouse example refutes the idea that genetic variability can only decrease.
That is, the inbred mouse population went from zero allelic diversity to some allelic diversity when the mutation arose.A population with only the genetic capacity to produce black mice developed the capacity to produce black mice and white mice. It seems like your underlying assumption is that the moment the white mice appear, all of the black mice die. This isn't the case - a mutation created allelic diversity that now produces two coat colors in a population that previously could only produce one. You've said this dozens of times, but you've yet to begin to support it. Perhaps you should stop using such absolute language until you have some evidence to back you up.

Mutation is a "process of evolution"; it is not independent from it. It is independent of selection, but not independent of evolution. Do you have any sort of reference or source to support this absolute statement? Off the top of my head - hemaglobin allelic diversity is maintained by selective forces. If an individual is homozygous wild-type, they are susceptible to malaria (the selective force); if they are homozygous for the sickle-cell allele, they have anemia. Thus the allelic diversity of having two hemaglobin alleles is maintained in the population, because heterozygous individuals are positively selected for.There it is - an example of selection maintaining diversity.You can take the "ALWAYS" off the front of your statements. Why do you think selection acts faster than mutation? You are so adamant about it, but you haven't provided any evidence for why you think the rate of the former is higher than the rate of the latter.

I'm beginning to think you are not arguing in good faith, since you quote-mined yourself. The first sentence you left out: So - maintaining diversity DOES contradict your repeated claim that "ALWAYS selection decreases diversity". Selection CANNOT increase variability, only mutation can increase variability (though selection could select for a genotype that was prone to mutation). But selection CAN maintain diversity once it is introduced into a population via mutation.Also, the hemaglobin example absolutely is typical of the processes of evolution. Nothing is going on with selection on hemaglobin gene mutations that is "atypical" of evolutionary processes.To respond to another point you make: How do you think the hidden variation arose? You talk about hidden variation as if it is separate of mutations, when hidden variation is the result of mutations.At a basic level, evolution proceeds by mutation and selection. Mutation increases allelic diversity, and selection maintains or decreases allelic diversity.Compare this to your own argument above: To paraphrase, "except for mutation (which increases allelic diversity), selection (the remaining "process of evolution") decreases allelic diversity.Perhaps you'll understand why I say that from my point of view all you are doing is describing scientifically accepted aspects of the theory of evolution, but with disbelief.

I haven't got to the point of being able to think about rates.

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That is very frustrating to read. Your entire argument is rates.Perhaps you should take Ned's advice and learn a lot more about the field before claiming to have its refutation.

We don't assume mutation, as Crash and Jazzns also state, we have direct evidence. Crash reiterated his haploid bacterial monoculture; I'll reiterate my inbred mouse coat color gene example.- The black mice were inbred, homozygous at all loci, with zero allelic diversity.- White mice appeared in one generation of the population.- The genetic difference that caused the whiteness was pinpointed in the genome (a single base change causing an recessive allele).- The black parents and black grandparents of the white mice were tested for this genetic difference.- The black parents were heterozygous for the white form of the gene.- The black grandparents did not carry the white form of the gene at all.If not mutation, then where did the white form of the gene come from?It could NOT have been preexisting variants, because if that was the case, the grandparent would have to at least be carriers for the white form of the gene, which they were not. This is not "assumption", this is fact.Do you believe that mutations ever occur?

Faith, since the above seems to be your mantra:
Specifically, what do you consider the "processes of evolution"?

Hey faith, I see you are still sticking to your use of the term "Processes of Evolution": I asked before and didn't get an answer. What are the Processes of Evolution? Would you please simply list them?