The End of Evolution By Means of Natural Selection

You're asking the wrong question. It isn't a matter of whether it "occurs in reality." It's a matter of what could ever stop it from occurring.Let's look at it from a slightly different angle. Can we agree that it is possible for none of the alleles of a gene to be optimal? In other words, can we agree that is possible that a tiny change (i.e., a point mutation, an error in a single nucleotide) to one of the alleles for a gene would transform it into an allele that is superior to any of the existing alleles?If we can agree on that, then what would prevent such a change from occurring? Nothing, right?Now, taking the human race as an example, realize that each individual has one new allele on average, and that around 134 million babies are born each year. Each baby contributes one new allele to the world population. Current estimates give us around 20,000 protein-coding genes, so that's 134 million new alleles for 20,000 genes, or around 6700 new alleles per gene, on average. Every year. Year after year. Endlessly.Unless all genes contain optimal alleles, beneficial mutations are inevitable.--Percy

Hi Faith,Over at the Reduction of Alleles by Natural Selection (Faith and ZenMonkey Only) thread in Message 76 you said: Since in your view the flood was real and four thousand years ago most species were reduced to only one pair of individuals, how can you characterize ZenMonkey's scenario as hypothetical? Since the only place for an allele to be stored is in a gene, and since in sexual species each gene in an individual can contain at most only two alleles, and since you believe mutations are not a factor, how could most species today have more than four alleles for any gene? Where are you putting these "built-in" alleles if not in the gene they belong to?--Percy

Hi again,So you are saying that a new trait arrives and then spreads as other traits diminish. So what exactly reaches an endpoint giving 'evolution less and less to feed on'? As far as I can tell even given your strict circumstances, as long as new traits are arriving I don't see any endpoints in sight. If the traits are not coming fast enough to match whatever the environment is doing then the endpoint is called extirpation or maybe even extinction. No extinction means that the new traits are getting there just in time to save the day. Of course your narrow scenario is not the only course of nature.Edited by CosmicChimp, : one more sentence

Oh, don't be offended! I apologize. You have questions that's not a sin, I never had anything against that. You actually have good questions. You won't listen to the answer and are tenacious but that's not all that bad, some people consider those qualities. See environment does define whether a trait is good or bad.

Hi Faith, I mistakenly posted this on the other thread, and was advised by admin that it was deleted (as that is a great debate thread), so I am reposting it here: These are the mysterious "hidden alleles" that you claim I have misunderstood -- either (a) you have not explained your position very well at all or (2) you are caught out on your make-believe scenario. Sadly, what this shows is that (1) you have not done the math, and (b) that whenever someone makes a statement that counters what you have said that you change the rules.In the real world what you have said just went from improbable to extremely improbable (improbable x improbable). No. Do the math.Generation 1

Parent Alleles	BT Black	BT Tan
BT Black	Black Black	Tan Black
BT Tan	Black Tan	Tan Tan

Generation 2

Parent Alleles	BB Black	BB Black	BT Black	BT Tan	TB Black	TB Tan	TT Tan	TT Tan
BB Black	Black Black	Black Black	Black Black	Tan Black	Black Black	Tan Black	Tan Black	Tan Black
BB Black	Black Black	Black Black	Black Black	Tan Black	Black Black	Tan Black	Tan Black	Tan Black
BT Black	Black Black	Black Black	Black Black	Tan Black	Black Black	Tan Black	Tan Black	Tan Black
BT Tan	Black Tan	Black Tan	Black Tan	Tan Tan	Black Tan	Tan Tan	Tan Tan	Tan Tan
TB Black	Black Black	Black Black	Black Black	Tan Black	Black Black	Tan Black	Tan Black	Tan Black
TB Tan	Black Tan	Black Tan	Black Tan	Tan Tan	Black Tan	Tan Tan	Tan Tan	Tan Tan
TT Tan	Black Tan	Black Tan	Black Tan	Tan Tan	Black Tan	Tan Tan	Tan Tan	Tan Tan
TT Tan	Black Tan	Black Tan	Black Tan	Tan Tan	Black Tan	Tan Tan	Tan Tan	Tan Tan

16 = Black-Black (25%)
16 = Black-Tan
16 = Tan-Black
16 = Tan-Tan (25%)After the second generation the pattern is the same, the frequency of alleles does not change (assuming every rabbit mates and produce more than one offspring etc etc as is assumed in the original population)Enjoy.Edited by RAZD, : added gridsEdited by RAZD, : found copy error mutation and removed

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I'm trying to follow along here quietly, but I'm having some trouble with things I don't know. I want to compare what Faith is suggesting with these innumerable front-loaded hidden alleles with the normal rigmarole of mutations and natural selection, see how the results might tend to differ, sort of a "thought experiment". I'm aware of the special problems in trying to imagine how an allele stays hidden for any significant number of generations, but that's not my main obstacle just yet.We normally tend to think of mutations, I imagine, as being dominant. That is, we talk about someone who has a phenotype that is unusual, perhaps they shoot ray beams out of their eyes or metal claws out of their hands, and we check them out to see how that happened, and when we look in their genes we see that they have a new gene that neither of their parents sample has in it. Unless I'm totally off base, this would be on only one of the two zygotes, yes? (why would the same thing go wrong with both zygotes of the gene?)So therefore, in order for it to be brand new in this individual, and also expressed in his phenotype, that one new trait in that one out of two zygotes would have to be dominant. But, is that how it really always happens? What I mean is, do we also get new mutations that are recessive? So then when someone is born with blue fur who can teleport, and we check them, we don't find any new genes that their parents didn't have. The mutation happened to some common ancestor back when, and the zygote has finally come together in a matched pair and the gene is finally expressed now.Does this ever happen? Does it happen about half the time? Or are they always dominant, in which case does relative dominance tend to show which genes are more recent than others?PS: Just to contribute something to the actual topic, yes, the above suggestion about how long it might take rare genes to come together and be expressed is about the closest thing to an argument I can see in favor of this hidden allele scheme. If a population is suddenly isolated, there's a much greater chance of incestuous pairings. Hard to imagine how there would be none at all until the isolation, though.

You are getting a bit mixed up here. Almost certainly what they have is rather a new allele a variant of one of the genes they inherited from their parents. A whole new gene woul be a very much rarer occurrence. A zygote is an embryo at the one cell stage after the germ cells have fused. I'm not quite sure what you are getting it confused with but possibilites would be allele, chromosome or parental gene copy.There is nothing stopping recessive mutations arising. The important thing is the exact nature of the mutation.TTFN,WK

Yes I am, thanks! Chromosomes. Alleles on each chromosome? I'm reading about genes being "heterozygous" rather than "homozygous". I guess that gets all muddled up when I try to express it as "one of the two zygotes". But fine, what I mean is, a mutation tends to occur on only one chromosome, not both, right? So then, to be expressed immediately in the first generation, it would have to not be recessive, yes? Yes, I had an idea like this to start with. That is, in a given pairing, black might be dominant because in that case it represents production of a pigment, whereas white might be recessive because all it represents is the non-production of the pigment. But then I read this Dominance (genetics) - WikipediaMendel's pair-matching math tends to make me feel slightly queasy after only a few iterations, sorry to be so stupid about it.If a mutation can be recessive, then it won't be expressed in the organism in which it occurs. This means that a gene may be "hidden" for some or even many generations in the evolutionary synthesis just as it could be in Faith's "no useful mutations" world.Is that correct?

An allele can be recessive to all other alleles, but not to itself. As soon as it is paired up with itself it can be expressed.--Percy

Right, so if Bob has a mutation (and I'm guessing that that mutation is liable to occur on only one chromosome of the pair he has) and that mutation is dominant, then it can be expressed right there in Bob. But if it is recessive, then it can't. And because it's a mutation, Mary whom Bob marries doesn't have it, and therefore even though about half of their kids have the new gene, it isn't expressed in any of them, because it is never reinforced. And Bob and Mary's kids dont breed, because society frowns on that sort of thing, so it doesn't get reinforced that way either.So, it isn't until several generations later, in some sort of "kissing cousins" scenario, before that gene might end up being homozygous for an individual and actually get expressed. It might never get expressed, it might get lost in the shuffle or just not get reinforced even though it persists through generations of outbreeding. Inbreeding might never occur, until suddenly one day Bob and Mary's descendant Phil gets trapped on a desert island with his wife Sally and they have two kids and then die off and those kids grow up feral and inbreed and produce children who have the gene reinforced and expressed and suddenly there are people with purple hair whereas there never were before, even though the gene for it has been in existence for many generations.Or not?

Sounds right to me, though some of the sticklers out there might quibble.--Percy

Right, which is why men are more susceptible to things like haemophilia and colour blindness, because the causative mutation occurs on the X chromosome in a region the male Y chromosome does not have a counterpart to so they only have 1 copy of the gene in question. Yes, a novel recessive mutation could easily not give rise to the phenotype for several generations, which means such mutations are good candidates for being lost due to drift.Your example of the desert island seems pretty much right to me.It is worth bearing in mind that there are many traits which don't fall into the simple dominant/recessive categories.TTFN,WK

Yes, good example, and it's also possible that a recessive allele whether a mutation or not could be selected against to the point that it is reduced to just a few in a large population, where the odds of its being expressed are very low, not impossible of course but very low, so that it could remain unexpressed for generations. So in my scenario, if, say, 20 individuals from that population, including 2 of these recessive formerly unexpressed alleles, migrate to a new geographic area where they become isolated from the former population, then the odds of this allele becoming expressed increase a great deal and it should appear pretty soon, possibly even in the very first generation after the migration. If it then also gets selected for some reason (some predator hates purple fur and only eats the other colors) then purple fur could become the dominating trait for that new population. Evolution in action. 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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Yes, good example, and it's also possible that a recessive allele whether a mutation or not could be selected against to the point that it is reduced to just a few in a large population,

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Not really. selection operates on the phenotype. A recessive allele will not be expressed in the phenotype of many individuals who carry the genes, so it cannot be strongly selected for or against.

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So in my scenario, if, say, 20 individuals from that population, including 2 of these recessive formerly unexpressed alleles, migrate to a new geographic area where they become isolated from the former population, then the odds of this allele becoming expressed increase a great deal and it should appear pretty soon,

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That could happen, although it must be pointed out that a population of 20 is small (on the limits of viability), and the odds of two having a rare recessive allele is not that high - and it must be very rare if it is never expressed.

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