But its uniqueness does not exceed the genetic complement of the "species."
Explain why.
And if it is a highly adapted (or genetically structured?) "species" (or breed/variety of the Kind) it most likely has a very limited gene pool.
Explain, surely a human is highly adapted? Perhaps you mean 'specialized'? What difference do you think this makes?
. If a species/variety/breed is highly adapted to a particular niche, aren't we talking about a pretty hardwired genetic situation anyway?
Hardwired? They obviously have a range of genes that will allow them to survive in that niche, but that range of genes depends where in that niche they are, and its a massive range in the vast majority of situations anyway. If said organism is capable of surviving in another, similar (yet different) niche, then they might migrate as population size increases so much that it makes sense to do so.
What IS the term for the genetic situation of the cheetah
I believe you have it about right, also one could say 'monomorphic'. Here is an
interesting study about it.
The study writes:
The cheetah is unusual among fields in exhibiting near genetic uniformity at a variety of loci previously screened to measure population genetic diversity. It has been hypothesized that a demographic crash or population bottleneck in the recent history of the species is causal to the observed monomorphic profiles for nuclear coding loci. The timing of a bottleneck is difficult to assess, but certain aspects of the cheetah's natural history suggest it may have occurred near the end of the last ice age (late Pleistocene, approximately 10,000 years ago), when a remarkable extinction of large vertebrates occurred on several continents.
I don't think this is of import to this conversation though, it doesn't seem to be anything to do with the cheetah being highly 'specialized', and even if it was, that just means nature abhors over specialization (which she does since changing times will lead to extinction, meaning the cheetah may well be an evolutionary dead end). So yeah, bottlenecks can cause serious problems for populations, especially ones to the magnitude that the cheetahs are hypothesized to have gone through (I've seen one hypothesis that goes as far as proposing only one surviving pregnant female after their near extinction event...many genes were lost...there's a nice 'pop' article on it
here.
A more technical look at bottlenecks can be found
here
So yes, I get it that each offspring has a unique genetic makeup, but the more specialized the species it belongs to the less genetic diversity was available to choose from.
I'm not sure if that's the case. Do you have any other examples of highly specialized organisms with this problem?
That is not so. What happened to Mendelian genetics if so?
Mendelian genetics is just the genetics of heredity. Without mutations, we'll just find that either the most dominant gene fixes into the population so that all members have it, or, if the dominant gene is selected against, it will vanish from the population. No novel features would arise, and the organisms will at best enter into an evolutionary stasis or will die off.
What does dominance and recessiveness mean if not something built into the population?
It does mean that very thing. The genes that are already built into the population. It is difficult to see how even a decent amount of microevolution is going to get underway with just Mendellian genetics to go off.
It can't be something conferred willynilly by mutation
I don't understand. A mutation occurs which forms something novel. The gene involved may or not be dominant depending on its makeup. I don't think 'willynilly' is proposed to be involved at any stage.
There are great numbers for some genes in some populations, small to even only one allele in others, and this has something to do with the built-in genetic picture as it gets worked on by the various Evolutionary Processes, not with random mutations.
Right, but wrong. The alleles frequency is 'built in' by mutations and natural selection. The 'gets worked on by the various Evolutionary Processes' happens by basically selecting out those alleles that do not survive to mating.
One organism has a random mutation that increases the thickness of its fur. It does not convey a disadvantage in this case and so the mutation gets distributed throughout the population. If 20% of a population has the 'thick fur' gene, then we would see it 1 in 5 chromosomes (this is the allele's frequency). If the environment was to get colder the thick fur gene may well increase the survival chances of those with the gene, so the frequency might change to 50%. Thus: mutations cause alelle changes, selection decides which allele changes stick around, and which ones get weeded out.
This whole process can be understood without reference to mutation at all, but only to normal built-in Mendelian genetics, to dominance and recessiveness and others I havenh't learned well enough, that is, to genetic potentials built into the genome that are reduced with each process of reproductive isolation
It can't be understood without reference to mutation. Without mutation, very little happens! If you don't reference mutation, you can't understand the whole process.
Mick did not mention mutation in his OP and did not mention it in answer to my discussion of the process either in his Message 29.
He mentioned it in the OP, but it wasn't the focus of his discussion since he was talking about the structure alelle differences in populations and their relations to geography, and how at small levels the same processes are at work as they are at bigger (more macro) levels. He wasn't really discussing the mechanism for those alelles getting there.
Yes, and this is because of the greatly reduced genetic diversity which severely limits or absolutely prevents the emergence of adaptive traits.
That is one cause for extinction yes.
Again, the more specialization, the more "speciation" in other words, the less genetic diversity, the less adaptability, the less capacity to "evolve."
I'm not sure this is the case. Maybe it is with regards to specilalization, but I don't see how more speciation leads to less genetic diversity. Speciation and specialisation aren't equivalent. And specialization doesn't imply low genetic diversity (that would need a major bottleneck) Its surely the case that a highly specialized organism is more fragile, but I don't see the case that a very light selective pressure can't change the course of a specialized but suitably diverse population.
I am convinced that macroevolution cannot occur, meaning that there are indeed fixed "Kinds" that can only vary -- and vary quite widely in many cases to remarkable differences in phenotypic expression -- but are always GENETICALLY definable as that Kind and no other.
That's fine.
I do not know how to define it but I am sure it will eventually be defined
That's OK too. The problem comes when the claim is made that macroevolution cannot happen, with no definition of macroevolution. How can one make an absolute statement with non absolute terms? Your statement is fine, its clearly worded as opinion.
. I continue to believe that the "mechanism" that "prevents" macroevolution is the very processes called Evolutionary Processes we are discussing because with the majority of them (except for recombination and mutation) every new phenotype corresponds with a reduction in genetic diversity which is inconsistent with evolutionary requirements
OK. I don't think one can look at the number of processes that 'select' versus the number of processes that introduce novel features (including epigenetics and mutation) and draw any sort of valid conclusion. I think the impact that each of these things have should be weighed.
Do you have any evidence that every new phenotype corresponds with a reduction in genetic diversity? It would be inconsistent with evolutionary requirements so it would be interesting to see this.
Mick is the only one who seems to be able to think about these processes in terms of ordinary genetics without the addition of mutation.
Because Mick isn't talking about how alelle frequency changes, he's just talking about the alelle distribution. Its only when you start bringing up objections of around new genetic information, bottlenecks, and so and start discussing the mechanism for alelle frequency change that we need to include mutations.
If you look at the OP, however, Mick clearly writes:
quote:
We can base our understanding of this data on the microevolutionary principles that Tamias amoenus arise from a single common ancestor and that the descendants of that ancestor have spread across the range, accumulating mutations along the way which have been preserved in each geographical region by heredity
Indeed, his entire point seems to be that the same process that results in microevolution (variations within a species, and from one species to another), seems to follow the same pattern as those observed at higher levels of evolution (approaching macroevolution? variations between genus), a genus would be something like Feline, Panther and Lynx, which I suppose isn't true macroevolution just yet, since after all, they are all still 'cats'. This is the reason I'm not sure of Mick's conclusion at this point. If he can expand to include higher (or perhaps it should be lower) taxonomic levels, I'd be more impressed.
It is puzzling to me that you and crashfrog talk as if mutation were the ONLY mechanism that confers diversity
Well, no, there are other factors, such as epigenetics as I previously mentioned.
as if you have no notion whatever of a built-in genetic complement which on its own accounts for the great majority of all phenotypic changes
Hmmm, maybe Faith, but you brought mutation up, I was just pulling you up on not including mutation's important brother, selection, which has led us to this point.
Its randomness would prevent the predictable Mendelian combos and the coherent structures that appear in nature just for one point.
Unless some kind of selection process was involved, sorting the 'bad' from the 'good' so that the 'worst' don't survive, and the 'better' ones mate more (thus increasing their frequency).
A change in allele frequency in the population is produced by the Evolutionary Processes that I have been discussing throughout.
Mutation and natural selection being the most famous evolutionary process to change the frequency of alleles.
All fecundity could possibly contribute is a speeded-up process of same.
Let us take an adult population whose size remains constant at 10,000 members. Each female has 24 offspring (2 litters of twelve for two parents) per generation so we end up with 10,000 adults and 120,000 children. Eventually the old adults die, and the children take up the mantle. However, the niche can only handle 10,000 adults so 110,000 children have to die. Only 9% of the kids get to mating age. There is tremendous struggle to survive going on here, and only those that are best at it manage. Given that all of the kids had a unique genome, and given that each one was a unique genetic mutant, only the genomes that convey an advantage survive, therefore the advantageous alelles brought about by mutation fix in the population, and the disadvantageous ones get weeded out.
Without fecundity the struggle to survive is massively limited, so deletrious mutations are more likely to acrue and fix. Fortunately fecundity exists and is an essential aspect of evolution as picked up even by Darwin.
There is absolutely NO way to get a handle on this picture of random wild mutation as THE mechanism for all change in populations.
It isn't THE change, that's why. First comes the mutation, then comes the selection. Other factors are at play, gene transfer, epigenetics and so on and so forth.
Unique genotypes occur NATURALLY without mutations. They are produced by the selection of, say, recessive genes instead of dominant ones by migration or some other process.
Well quite, but I don't think a population which had no mutations would last long unless it started with high genetic variety. I don't think it would ever speciate (ie become sexually incompatable with its ancestral population) either. Not a whole lot would happen at all really. And of course, this screws asexually reproducing organisms royally....every one (well a great deal anyway) would be a perfect clone of its ancestor.
This exclusive mutation explanation is false on the face of it, as it denies the normal Mendelian ooperations
Well that's not true. Mendelian operations tell us about heridity, and functions perfectly with the mutation explanation, which as I have said in this post and in others is not proposed to be an exclusive explanation, indeed, it cannot be an exclusive explanation, but neither can it be ignored when discussing population genetics.
What is Mick talking about in his Message 29 then, since he is not talking about mutations?
Looks like he is talking about phylogeography and the well established and accepted evolutionary processes. He doesn't specify what those established evolutionary processes are, since he doesn't go into detail about the nature of these processes he is unlikely to discuss mutations, epigenetics, gene transfer, selection etc is he?
Tell me, what was mick talking about in
Message 1 when he said:
Mick writes:
We can base our understanding of this data on the microevolutionary principles that Tamias amoenus arise from a single common ancestor and that the descendants of that ancestor have spread across the range, accumulating mutations along the way which have been preserved in each geographical region by heredity.
This message has been edited by Modulous, Mon, 28-November-2005 03:50 PM to fix a maths error
This message has been edited by Modulous, Mon, 28-November-2005 04:48 PM
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