The End of Evolution By Means of Natural Selection

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Its homozygotes would have been selected against -- their phenotype. Couldn't that cut back on the number severely?

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Unless the allele is very common heterozygotes will outnumber homozygotes. And if it is that common there will still be a lot of heterozygotes left. So unless there are some special conditions which somehow change things the answer must be that it is very difficult to make a recessive allele rare through selection. If there is really severe selection against the homozygous individuals then it might decline slowly, but it will be slow. (Genetic diseases are usually recessive because those that aren't are eliminated by selection.)

Hi Faith,Of course it's evolution in action - it just isn't speciation in action.Your scenario is unlikely but not impossible, but even if newly emerging traits that you think will happen are for physical or behavioral differences that prevent breeding with the original parent population they are still interfertile. The offspring are still genetically members of the original parent population. As long as the genomes of the parent and daughter populations remain strict subsets of the original parent population then they remain the same species genetically. If the only differences are allele combinations then the sperm will still fertilize the egg. The differences have to be on the order of genes and chromosomes before two populations can become genetically infertile with one another.--Percy

What about the 65 million base substitutions seen between humans and chimps? About 2% of the bases are different between the human and chimp genomes, and a 5% difference if you include additional or absent DNA sequences (i.e. indels). According to your logic, humans are heavily diseased chimps, or chimps are heavily diseased humans, take your pick. In fact, every species is heavily diseased because each species differs from the next in the DNA. If you are going to hold on to the argument that mutations only lead to disease then we should only see a single species, or the genome of each species is made up of different alleles that share 100% homology with another species.Or you can face the music. DNA can be different. Those differences are responsible for each species adaptations that they require to survive in their niche. This leaves you with a rather large challenge, showing which differences can not be produced by random mutation. So which of the 65 million DNA differences between chimps and humans produce disease? Using your 1% figure here I could only assume that each human is suffering from 650,000 genetic diseases. So you are saying that none of the differences between humans and chimps is beneficial to humans? The actual evidence is the genome of every species which can differ greatly in their DNA sequence by thrive nonetheless.

Hi Percy,
Many times I've said that speciation isn't necessarily the result of any particular population split, especially one from a highly variable parent population, that it would most likely occur at the end of a chain of population splits such as in ring species, after many number-reducing, trait-reducing, allele-reducing events, each new population splitting off from the previous population, or it could occur more rapidly in a more extreme split such as bottleneck. It's the trend I try to emphasize, the trend of genetic reduction accompanying new varieties, not the end result itself, which may or may not occur.I'm still on my break though. Back to deal with the heftier posts later.

Hi Faith,How do deal with the fact that in your scenario parent and daughter populations will always be genetically interfertile. When there's a one-for-one match between genes and chromosomes, then they're the same species. Mixing up the alleles won't change that.--Percy

Here's one scenario I've given before. It does not mention mutations at all, merely isolation, selection and drift within two populations that split from each another, as the forces that bring about inability to interbreed. A smaller daughter population would only increase the effect.Isolation means it will mix its own much reduced and randomly assembled complement of alleles together which will produce its own characteristic phenotypes from that mix, and develop an appearance quite different from the parent population.This has always been regarded as evolution, change in gene frequences you know, and population geneticists also see speciation coming out of these same processes. Again here's that diagram, which shows what is described, the diagram calls it Speciation:
File:Speciation modes.svg - WikipediaThis is such standard evolutionary stuff from all I've read I'm still really amazed there's so much objection to it. Edited by Faith, : No reason given.Edited by Faith, : No reason given.

We're not objecting to "evolutionary stuff." We're only pointing out where you've misunderstood "evolutionary stuff."Again consider a parent population with 26 genes A through Z and four alleles 1 through 4 for each gene. We can refer to individual alleles as B2 and X3. We'll keep it simple and say that it has one chromosome that looks like this for one of the organisms in the parent population: Any other organism that has the same 26 genes A through Z and the four alleles for each gene 1 through 4 is genetically compatible and can breed with it. As long as both parent and daughter populations maintain strict subsets of the allele set of the original parent population then they will be genetically compatible and be interfertile. You'll never be able to come up with a combination of alleles for which this isn't true. For example: Look at that, Faith. Every gene matches. No matter how you change the allele numbers (in your scenario the genes are fixed and never change), the genes match every single time, and the alleles being combined for each gene are the exact same alleles that already existed in the parent population and that in that population were successfully combined during reproduction for generations.Your scenario is not what we observe in nature. As much as you yearn for speciation to be caused by allele reduction, that's not what we see. What we observe in nature is that the more genetically different organisms are the less likely they are to be genetically compatible. That's because much of the difference arises from mutations creating alleles that the original parent population never had. Mutations also create and destroy genes and entire chromosomes.Take the cat family, for example. The more distantly related genetically that two cat species are, the less likely it is that they'll be interfertile. Lions and tigers are interfertile (sort of - the offspring are often sterile). But lions and housecats? Very unlikely, because they're too different genetically. Just as chimps and humans are obviously closely related but have differences in both their genes and chromosomes (and, of course, their alleles), so do various species of cat. Speciation in both hominids and cats and most other creatures quite obviously did not take place through allele reduction.I again advise you to focus your energies on the Reduction of Alleles by Natural Selection (Faith and ZenMonkey Only) thread.--Percy

And here's another example. Note the TITLE on this You Tube video,https://www.youtube.com/watch?v=s4kiOnUW5a4That's the population genetics video Cosmic Chimp linked some time ago that I've only half watched. Got bogged in the math part. It looks simple enough for even me to learn it but I haven't sat down to work it through. Mr. Chimp said my particular concerns will be discussed in the second of the series -- how variability is maintained. Does rather suggest that there could be a drain on variability it that needs to be overcome but I'll see when I get to it. Meanwhile the title alone says a lot: How SELECTION Changes the Genetic Composiion of a Population. Merely selection, no mutations mentioned.Selection changes the genetic composition of a population.So does simple isolation as may occur with drift within a population or geographic barriers encountered through emigration etc. Edited by Faith, : No reason given.

You're arguing with the Wikipedia article as much as me although you claim not to be.But I'll have to deal with it later.Edited by Faith, : No reason given.

Wha??? Then you didn't watch the video, because he mentions mutations at :41 seconds into the video, Faith.Verbatum from the video starting at :41 sec -thru- :54 sec:

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A mutation has occurred that had an effect on a process or a structure, and if it increased the reproductive success of the organism it was in, it was retained by evolution; and if it did not, it disappeared.

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Maybe you missed it?- Oni

Somebody a while back asked me where I got the idea of "thousands of genetic diseases in human beings." I knew I got it from somewhere on the web but when I went googling for it I couldn't find it, only lists that manage maybe a hundred or two hundred or so.BUT just now sorting through my bookmarks I found that I'd very prudently bookmarked the source of the idea and then completely forgot about it and never thought to go back to it. Whether it's a particularly "reliable" source or not I can't determine for sure but it's very much devoted to questions scientific:

No I didn't miss it. Of course he's going to define evolution including mutations as the source of all alleles.My point is ONLY that selection alone is given in the title as the cause of changes in genetic composition and such changes can be discussed completely with reference to selection alone without reference to mutations. Presumably the alleles are already there by mutation and then selection acts on them in this scenario.Evolutionists NEVER leave out mutations, they'll always get around to them eventually, and I would never claim otherwise. BUT they also describe processes such as selection as bringing about evolution independently.Edited by Faith, : No reason given.

I again adivse that you focus your energies on the Reduction of Alleles by Natural Selection (Faith and ZenMonkey Only) thread where ZenMonkey is walking through the issues exceptionally carefully and methodically, but if you decide to continue participating in this thread anyway then please respond to the problems I posed for your scenario in Message 442.About the video you say: Of course selection can change the allele frequency of a population without any contributions from mutations at all. But while the word "mutations" is not in the title, the lecturer mentions mutations at around the 40 second mark before the first minute is even up. No, Faith, I'm not arguing with Wikipedia. The conclusions you're drawing do not follow from anything Wikipedia says. You'd be much better off taking things one step at a time with ZenMonkey in the other thread.--Percy

It is true that one can talk about the effects of selection independent of mutation, and that's just what one would want to do in an introductory course on evolution. Everyone agrees that selection alone is sufficient to bring about evolution, but not speciation. That video provides no support for your view that reduced allele diversity causes speciation.--PercyEdited by Percy, : Fix bad grammar.

The title says, How selection changes the genetic composition of a population. Not that selection alone changes the genetic composition. Obviously the how is what the video gets into explaining.It would be like watching a video called, How Einstein change Physics, then claiming the title says nothing about relativity being how Einstein changed physics.{ABE} Posted before I saw Percy's response.- OniEdited by onifre, : No reason given.