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Author Topic:   The End of Evolution By Means of Natural Selection
subbie
Member
Posts: 3358
Joined: 02-26-2006


Message 16 of 851 (551991)
03-25-2010 5:01 PM
Reply to: Message 15 by Faith
03-25-2010 4:45 PM


Re: (Subbie) Am I ignoring reproductive isolation?
Faith writes:

The point I'm making is that WHEREVER EVOLUTION IS GOING ON, THAT'S WHERE you'll have a reduction in genetic diversity, and that is completely at odds with the theory of evolution.

This is simply not true. As an example, let's discuss Darwin's Finches, 15 different species of tanagers that Darwin found on the Galapagos islands. The most important difference among the various species is the size and shape of their beaks. These differences did not come about by the elimination of alleles, but by changes in alleles in different populations, resulting in different species. Thus, in this example, evolution resulted in an increase in genetic diversity. In fact, this sort of increase in genetic diversity is what is most commonly seen in speciation events.


Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus. -- Thomas Jefferson

For we know that our patchwork heritage is a strength, not a weakness. We are a nation of Christians and Muslims, Jews and Hindus -- and non-believers. -- Barack Obama

We see monsters where science shows us windmills. -- Phat


This message is a reply to:
 Message 15 by Faith, posted 03-25-2010 4:45 PM Faith has responded

Replies to this message:
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Percy
Member
Posts: 13287
From: New Hampshire
Joined: 12-23-2000
Member Rating: 1.6


Message 17 of 851 (551992)
03-25-2010 5:11 PM
Reply to: Message 15 by Faith
03-25-2010 4:45 PM


Re: (Subbie) Am I ignoring reproductive isolation?
Hi Faith,

Genetic diversity can go in any direction after reproductive isolation. For example, consider a relatively homogeneous population that becomes divided in two when a river changes course. There are now two populations, both with pretty much the same alleles and allele frequency. Mutations experienced in one population will no longer be shared with the other and the populations will evolve along different paths. If this continues for a sufficient period then they could lose their mutually interfertile quality and become two species.

If both populations thrive then diversity could increase in both. But if one or both populations suffer some disaster such as flood or famine or an invasive predator or disease that greatly reduces population size, then diversity would be reduced. It all depends upon what happens to the populations.

--Percy


This message is a reply to:
 Message 15 by Faith, posted 03-25-2010 4:45 PM Faith has responded

Replies to this message:
 Message 58 by Faith, posted 03-26-2010 2:04 PM Percy has responded

    
Rahvin
Member (Idle past 137 days)
Posts: 3943
Joined: 07-01-2005


Message 18 of 851 (551994)
03-25-2010 5:17 PM
Reply to: Message 9 by Faith
03-25-2010 3:58 PM


quote:
Hi Faith. Welcome back.
The problem behind your theory is that it's contradicted by real-world observations. Your predictions are invalidated, because observed evolution has not been reducing genetic capacity for variance.

Hi Rahvin. Actually, observed evolution does demonstrate this when you focus on endangered species. It is probably not Natural Selection that has brought about their endangered condition since supposedly that would be adaptive and not endangering, but it is brought about by processes that isolate a small portion of the genetic variation formerly available to the whole population, which is just a more drastic version of what NS does. As I imply above in my response to Paul K I believe perfectly viable healthy populations can develop from such random reductions in genetic diversity, as most likely is the case in Ring Species. A decimated population such as the seals which were hunted to near extinction, may actually come back in large numbers, but they will come back with much reduced genetic variability compared to their original population. Surely this is obvious? Unfortunately in many cases such a situation does threaten the survival of a species and conservationists are always having to deal with these situations.

You seem to have an odd understandong of what natural selection entails. The Theory of Evolution predicts that extinctions will happen. Endangered species are the result of a set of adaptations that no longer apply in a changing environemnt. Since mutation is largely random, the process of developing new traits is slow, and changes in the environemtn can be relatively rapid, there will always be cases where changes in the environemnt will occur too rapidly for a population to adapt effectively, and they will either be killed outright or gradually out-competed for resources by better-adapted species.

None of it has anything to do with some sort of reduced potential for adaptation. You certainly haven't provided any evidence that there is any finite limit for genetic variance over long timescales. You've simply asserted it to be so.

Reductions in the numbers of a given population does indeed result in a "genetic bottleneck" where extant genetic diversity is lost. If families A B and C die out while family D lives, certainly the currently available genetic diversity inthe total population has been reduced. But that says absolutely nothing about the potential of mutation.

The only real problem with a reduction in genetic diversity as in a non-extinction die-off is the danger of recessive traits being passed around and expressed, not some "mutation barrier." If a population is shrunk to a sufficient degree, the lack of genetic diversity can threaten the population's longevity because of those rexcessive traits until reproduction allows natural mutation to restore diversity. Human beings had an extreme population bottleneck some thousands of years ago, yet look at our diversity today.

quote:
Year after year, undergraduate students directly observe evolution in action as they show changes in allele frequency in fruit flies. Other students observe the case of drug resistance spontaneously forming in a population of bacteria.

It's certainly true that we don't have to worry about fruit flies and bacteria becoming endangered species. You are going to have to prove to me that you can get significant changes in fruit fly phenotypes without a reduction in genetic diversity, that is, you can bring about a new population characterized by this change without losing genetic diversity.

What's your criterial for a "significant change?" We can easily get child populations that no longer interbreed, change the color of their eyes, etc.

But remember, Faith: in any observed "branching" of populations into divergent and distinct subgroups (whether actual speciation has occurred or not), total genetic diversity has increased, even if each indivdual subgroup now has less diversity than the parent population.

As for bacteria I'm not enough up on the genetics involved, but what you are describing is some sort of mechanism for increasing their variation, not the selection that reduces it, which is what I'm focusing on.

It's both. The experiment involves growing a large population of bacteria from a single cell. All of the child bacteria should be identical clones of the original. The population is then exposed to an antibiotic, which drastically reduces the population - in effect, it eliminates all genetic diversity except for those organisms which include a resistance to the antibiotic. It's used to demonstrate the fact of mutation (since a new trait that was not present in the original parent forms; it's a new trait that was not inherited, the very definition of a mutation)...

But it also works well to discount your assertions. When the population is allowed to continue to grow with regular exposure to the antibiotic, the resitance trait remains expressed by the vast majority of the population because those without it are quickly killed off. But when the antibiotic is removed (an environemntalchange) the resistance no longer confers any survival advantage, and will slowly decrease in representation among the growing population.

In other words, even after genetic diversity is reduced in a population reduction, diversity will continue to increase.

HIV treatment is particularly sensitive to this fact. Believe me, I wish HIV had a "mutation threshold" that could not be passed. Unfortunately, that;s not the way it works. Once a strain of HIV develops resistance to a given antiviral drug, it can and will continue to mutate rapidly, and can develop resistances to new drugs as well. This is why HIV treatment usually involves two or more completely different antiviral medications right from the beginning - if resistance to Drug A develops, the retrovirus should still be susceptible to Drug B, and so on. It;s effective so long as the selective pressure is continued by continuing to maintain a high level of all of teh medications in teh patient's body...but as soon as the pressure is lessened (say, within a month or two off of the meds), the viral population will have grown and diversified to the point that the patient now risks resistance even to both drugs.

Their ability to evolve a drug-resistant strain even when reduced to a single allele

Not a single allele. A single cell. Very different.

is very interesting but it MUST be accompanied by a severe genetic reduction leaving ONLY the allele for that particular strain no matter how the original came about. Or are you claiming that you see a multiplication of new alleles from a condition of total genetic depletion?

Essentially, yes. See above. Populations that have been reduced to a single member (in other words, zero genetic diversity) will spawn populations with lots of diersity, even to the point of acquiring resistance to medications.

Again, even if you are, again this is increased variation, not selection and when you have it you no longer have evolution, you no longer have a drug-resistant strain or whatever else you were aiming to get.

Evolution never stops. So long as mutations are passed down from parent to child, natural (or artificial, in teh case of lab experiments) selection will continue to increase the frequency of beneficial traits while decreasing the frequency of traits that are not beneficial.

In the bacteria experiment, mutation increases diversity. The antibiotic exposure selects, by eliminating non-resistant bacteria and thus reducing total current diversity. The population, when allowed to grow again, will again increase in diversity due to mutations - such that a subgroup of the main population may develop resistance to a different drug, and so on.

It's selection and isolation that bring the desired trait to expression in the phenotype,

Wrong. Evolution is not reactive. The resistance trait (in our example) must already exist in the population before the antibiotic is used. The population does not generate resistance as a response. Until the antibiotic is used, the resistance is simply a random mutation that confers no benefit and thus enjoys no greater representation in the population as a whole than any of the other uncounted mutations ina diverse population. Only when theselective pressure of the antibiotic is introduced does the already-existant mutation suddenly confer a survival advantage to the subgroup, and the trait will rapidly increase in freqency as the competition is killed off by the antibiotic.

drug resistance in the case of bacteria, and this always involves decreased genetic variability. At least you haven't shown me how it doesn't.

The selective pressure reduces extant genetic diversity by killing off large numbers of a diverse population. But mutation continues to increase diversity even after the population ahs been reduced (just like it did when we started with zero diversity in a population of one).

quote:
The process doesn't stop. Variation continues, unimpeded. There is no reduction in the possibilities derived from mutation guided by natural selection. At no point to we reach an evolutionary "endpoint" where no more change is possible.

There may, hypothetically anyway, be no "reduction in the possibilities derived from mutation," but when you add "guided by natural selection" you are implying something that can't in fact happen. Natural selection "guides" by doing what I've been describing, by eliminating all that variation mutation has brought about so that the selected variant can come to characterize the population.

Not all. Some. Natural Selection is not some rampaging genocidal agent running around killing everything.

Natural selection is simply the process by which beneficial traits tend to increase in a population because those who possess those traits will survive to reproduce more often than those with non-beneficial traits. More often does not necessarily mean to the exclusion of. In a given environment, animal A may be "better" adapted than animal B, but that doesn't necessarily mean B will go extinct.

quote:
And that's just the examples that we directly observe. The fossil record and the other extant life we see today has variety beyond comprehension.

{Edit: I have to add in here somewhere a warning to myself as well as you that it's easy to get the terms "variation" and "variability" and related concepts confused with each other and even lose the whole point. This has happened to me and I'm trying very hard to avoid it but it will probably still happen. The fact that there is lots of VARIETY in nature, in phenotypes even within the same species, is a different matter from the amount of genetic VARIABILITY that is present in a population}

The fact that great variety exists in nature is a very good thing, but this doesn't change the fact that when evolution occurs in a population it HAS to reduce genetic diversity. That's the only way you get a new variety.

False. COmpeltely false.

Evolution happens when an existing population diversifies and branches off into distinct sub-populations. That doesn't necessarily involve the extinction of any of the child populations or even the disappearance of the parent. Diversification typically happens due to environmental changes, as random inherited mutations suddenly become beneficial or detrimental. Often this happens when some of a given species migrates to a new area, and thus a new environment with different selective pressures. In this case, even though the migratory population will end up distinct from its parent, the parent population still exists, and thus diversity is increased.

I have to postulate that there used to be much much more variability in all species than there is today in most species, BECAUSE of the evolution that has been going on creating new varieties (or "species" if they can't interbreed with their parent population) over millennia. Some species retain enormous variability nevertheless -- dogs for instance. The most amazing varieties of dogs have been brought about and yet they can still interbreed -- THAT's enormous built-in variability there. But other species don't have that much variability, or have lost it in their successive branchings down the centuries.

Provide evidence that other species do not possess the capacity to be bred as dogs have or retract.

I'll do one better though: we can breed all manner of plants and animals with a very great degree of diversity. Do you have any idea how different the corn, banannas, grapes, cows, pigs, or really any domesticated animal or plant has diverged from the original natural stock? How much diversity we still have amongst those populations while retaining the ability to interbreed?

Which organisms, precisely, lack the potential to be bred to extreme degrees of diversity, and how do you know this?

Consider the dog example while we're at it. Every breed of dog MUST show reduced genetic variability compared to its population of origin because if you want it big you're going to have to eliminate everything that tends to smallness, if you want it good natured you have to eliminate everything that breeds for ferocity, and so on.

Reduction in the frequency of one trait does not necessarily reduce the frequency of all other traits in teh same organism, Faith. Just look at all of the "small" dogs we have, their differences in fur, coloring, temperament, intelligence, etc. You can breed for a specific result ("bigness" or "smallness") and still increase total diversity.

Dogs as a species have enormous genetic variability but a particular dog variety or species has to have very little.

You mean a sub-population will have less diversity than the total population?

Why would we ever assume otherwise, Faith?

If A = B + C, B and C will always each be less than A.

You are ELIMINATING alleles in order to bring about your favored breed. Assuming that natural selection operates in a similar fashion in nature, that's what has to happen there too. You are not going to get a new variety, breed or species without a loss of genetic variability. This is really a law of genetics.

This is really a case of you not understanding genetics. You can reduce the frequency of a single trait without affecting the frequency of other traits, including the appearance of new traits.

You can reduce a population of bacteria to one individual, meaning zero diversity, and end up with a highly diverse population that has even developed new traits like antibiotic resistance.

Your premise is utterly false.

quote:
The genetic and morphological evidence for common ancestry of virtually every living thing on the planet is overwhelming, to the point that it's better established than the Theory of Gravity. Given that this is the case, and populations continue to diversify into distinct sub-groups before our very eyes, it would seem that your premise, that evolution should grind itself to a halt through some sort of genetic entropy, is falsified.

The evidence for common ancestry is going to have to be rethought if it turns out that evolution beyond a series of built-in variations is impossible because of the laws of genetics.

Indeed it would have to be rethought. Fortunately for biology, you've presented no evidence or argument that challenges the Theory of Evolution in the slightest.


This message is a reply to:
 Message 9 by Faith, posted 03-25-2010 3:58 PM Faith has responded

Replies to this message:
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Faith
Member
Posts: 16206
Joined: 10-06-2001
Member Rating: 1.4


Message 19 of 851 (551999)
03-25-2010 5:54 PM
Reply to: Message 8 by Phage0070
03-25-2010 3:16 PM



I would like to try to deal with every argument in this thread so I may get bogged down with a particular poster from time to time, as with Phage here, if I can't quite grasp what is being said. (I'm not going to answer Coyote of course. Nobody's conceded evolution is lost yet so wait until that happens ).

My argument is that natural selection and genetic drift, all the processes that select or isolate a portion of a population, do bring about the change called evolution but also always reduce genetic variability, which is the opposite of what evolution needs.

That is true; if only a subset of the population reproduces then the variability in the set that did not reproduce is lost.

Well stated, thanks.

Your argument appears to be based on the concept that because a subset of all possible mutations is being selected, the population must necessarily trend toward a single genetic standard.

I'm not sure I'm following you here. I've been keeping my focus as much as possible on a SINGLE mutation (or allele) for the sake of simplicity and clarity (I hope), knowing that of course reality is much more complicated -- rather than a "subset" of mutations, but perhaps that isn't the problem for me so much as "a single genetic standard."

That's what loses me I think. Being focused on a single mutant or allele means I'm focused on a single trait and tracing it through a number of generations in which it is reproductively "successful" as they say, during which series of reproductions it gradually replaces (eliminates) other alleles for the same trait that are continuing to be passed down by other members of the population as well, only not with quite as great success.

Eventually this allele will replace them all if the selective pressures or other factors continue to favor it reproductively. This isn't a concept I start with, it's where these processes end up. So I'm not assuming anything about a "single genetic standard" which I don't think I understand in any case, but constructing an argument to show that selection and isolation single out a particular trait by eliminating all its competition and ultimately make that trait characteristic of a new population that emerges from these processes.

Having said that let me try to grapple with the rest of your post:

To illustrate where this goes wrong, consider this hypothetical bloodline:

An organism has 5 genetically distinct offspring (they each have their own unique variations). Two of these do not reproduce, the remaining three having been "selected".

OK, a source of confusion for me is that you have so many different variations going on whereas I've been trying to keep the focus on one at a time. But I'll try to follow you out. So we now have three offspring that will go on to reproduce. The focus shifts from a single allele for a single gene to a whole genome full of variations from which what is being selected is beyond our ability to know.

All I can say is that EACH of these selected individuals, as long as its offspring remain "pure" and its line continues to stay selected, not sharing genes with the other selected individuals, will progressively lose genetic variability down the generations as its traits become established in those generations to the point of forming a new population. The likelihood that there will be no interbreeding with the other lines is very low, however, and therefore the likelihood of preserving the selected type is low, so it's doubtful whether we're even talking about the processes of evolution I have in mind. (Each "selected" line would have to move to its own private isolated island to show what I'm trying to show).

These three in turn have 5 genetically distinct offspring each, 2 each of which do not survive (6 lost, 9 reproducing).

You seem to be claiming that because the theoretical possibility of having 25 genetically distinct organisms descended from 5 bloodlines is being reduced through selection, that the genetic diversity must necessarily trend toward zero.

The genetic diversity in EACH of those "bloodlines" DOES necessarily trend toward zero AS LONG AS THEY MAINTAIN ISOLATION FROM OTHER LINES. You have to keep the focus on the SINGLE line that is evolving, even if there are three or five separate such lines. In EACH line the traits will be changing according to the "founder" at the SAME time alleles for competing variations on those traits will be replaced or lost, and finally ultimately completely lost if the line ever reaches the point of speciation or inability to interbreed with its cousins.

The problem is that in this example we are left with 9 genetically distinct organisms descended from 3 distinct bloodlines, when we started out with one.

The series [1, 3, 9] does not appear to trend toward zero in my view.

I did have to take this step by step because it was hard for me to follow, but now I think I can say that the problem here is that you are treating the number and variety of "grandchildren" as a collection rather than as a line of evolution. Or something like that. As long as they remain part of the same population with the constant possibility of interbreeding you don't have evolution as I am describing it. Yes, any individual with its genetic peculiarities COULD be the starting point of a completely new evolved population, and yes, any reproductive success is a step on the way to evolution, but you've got to eliminate gene flow and favor/select a particular line to the COMPLETE EXCLUSION of other lines to get what I'm trying to point out here. That's where you see the trend to reduced genetic diversity.

In your scenario, assuming the trend continues, you will continue to get new generations of genetically distinct individuals, some passing on their distinctions, some not, but in the end you're only going to have a bigger population of the same species with all its usual variation and variability scattered throughout. Genetic drift (or if you prefer the "selection" that confers reproductive success) will probably have altered its overall "look" somewhat by that time, but this isn't evolution in the strict sense. It's a very healthy state for a population to be in, but it's not evolution except in the most trivial sense.

I hope I grasped your point.

Edited by Faith, : added a line


This message is a reply to:
 Message 8 by Phage0070, posted 03-25-2010 3:16 PM Phage0070 has responded

Replies to this message:
 Message 23 by Phage0070, posted 03-25-2010 7:04 PM Faith has responded
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Faith
Member
Posts: 16206
Joined: 10-06-2001
Member Rating: 1.4


Message 20 of 851 (552002)
03-25-2010 6:47 PM
Reply to: Message 10 by nwr
03-25-2010 4:05 PM


Greetings, nwr:

My argument is that natural selection and genetic drift, all the processes that select or isolate a portion of a population, do bring about the change called evolution but also always reduce genetic variability, which is the opposite of what evolution needs.

That's not quite right. Yes, selection reduces variation.

More to the point I'm trying to get at, it reduces genetic variability or the number of alleles for the trait selected.

As far as I know, genetic drift does not affect variation. And mutation increases variation.

Yes, mutation increases variation (although I'd point out that it does so by replacing another probably quite viable allele, and since many mutations are not desirable, the net effect may be a loss but I digress) and according to the Wikipedia demonstration I linked, which I will link again here, genetic drift DOES reduce variation and variability. And it makes sense that it would since the idea is that it brings about a change in gene frequencies just as all the other evolutionary processes do, only through a sort of random selection process within a population.

You are correct, that if there were only processes that reduce variation, then eventually evolution would run out of variation and would stop. But as long as there are also processes that increase variation, there is no reason to expect evolution to stop.

I have to refer you to my answer to Paul K here. This isn't a simple addition/subtraction. The subtraction that is done by the selective and isolating processes (NS, drift, bottleneck etc.) actively GETS RID OF competing alleles for that trait. So if by some highly improbable chance mutations simultaneously produced thirty new alleles for the trait (again by replacing thirty of a type that was probably perfectly viable in thirty individuals) IF ONE OF THEM IS SELECTED AGAINST ALL THE REST, then all the rest might as well not have existed at all as the selected one will gradually (or possibly rapidly) eliminate them all.

Of course under some circumstances in which the selected trait gets completely isolated from the mother population those many new traits may continue on in the greater population, but as far as the selected population goes, it will gain its new adapted phenotype THROUGH the loss of all the other alleles. And then that mother population with all the new traits will have an interesting array of variations at that locus (29 different hair types, 29 different coat patterns, 29 different ear shapes or whatever) but this isn't evolution, unless you want to completely rethink and redefine what evolution is. According to the usual definition, announced quite persistently by Dawkins for instance, it's always evolution BY natural selection, that's what evolution IS.

As far as I know, what is mostly noticed is that variation stays fairly constant.

In populations where evolution is not going on this is true. I believe that was the observation embodied in the Hardy-Weinberg principle.

A bottle neck, such as caused by isolation of a small population, can result in reduced variation.

No doubt, it DOES, and severely reduced GENETIC variability too. Along with some very interesting phenotypes that may even qualify as new species.

But the variation is rebuilt during succeeding generations.

I bolded that statement because I believe that is wishful thinking that is not borne out in reality. If this were true conservationists wouldn't be wringing their hands over the small numbers of salmon that get themselves up a tributary where undesirable reproductions bring undesirable traits to the fore along with extremely reduced genetic possibilities for further change; and there wouldn't be a club for the preservation of the cheetah. While all along in this discussion I am assuming for the sake of argument that useful mutations do occur at a rate that allows them to become the basis for selected traits, in reality this simply doesn't happen, as all too many conservationist scientists in the field ought to be able to testify.

HOWEVER, AGAIN, EVEN IF the variability COULD be rebuilt, you'd STILL be facing the exact same situation. You'll either once again have a nonevolving population, OR with selection a portion of it will vary/evolve possibly on out to speciation as it loses its genetic variability. When there is active evolution, the production of new phenotypes, there is also genetic loss. I know the objections to this are going to die hard, and may not die at all, but if they don't it will be through denial.

The type of argument you are making could perhaps be used to suggest that the theory overemphasizes selection and underemphasizes the production of new variation. But you won't be able to refute evolution this way, because the empirical evidence shows that variation does build up again if it has been reduced - unless, of course, that particular line goes extinct.

Here I shall request that you produce this empirical evidence. The cheetah has lasted quite a long time without going extinct AND without acquiring one iota of variability. Perhaps someone should look into that population of seals that grew so large after being nearly exterminated -- Bet you a good collection of DNA samplings would confirm seriously reduced genetic diversity among them. Somebody get a grant to read thousands of genomes from the different populations in a ring species -- salamanders, seagulls, chipmunks, all of the above, or find a small highly variable creature and create a ring series in a laboratory for the same empirical test. I predict that the further you go down the series the less genetic variability you will find. If I had the wherewithall to fund such a study, believe me I'd do it.

Edited by Faith, : No reason given.


This message is a reply to:
 Message 10 by nwr, posted 03-25-2010 4:05 PM nwr has responded

Replies to this message:
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RAZD
Member
Posts: 15946
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 1.8


Message 21 of 851 (552003)
03-25-2010 6:47 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


Hi Faith, and welcome back.

It seems to be generally overlooked that for evolution to occur, alleles must be eliminated, thus reducing genetic diversity.

Perhaps, or it could increase diversity by dividing various groupings of alleles in different ways in different subpopulations.

Are there more or less alleles in the total genomes of chimpanzees and humans than there were in their common ancestor? Given that we share 95 to 98 percent of DNA between the two, but that each species has alleles that are not shared, then if there is a common number of alleles in a species it seems that the sum of two species must have more alleles than a common ancestor could.

You can add as many new alleles as you think mutation can come up with at any point in this progression, but when these selection and isolating processes go to work on them the very same thing happens.

If you think of a jar full of water, then adding water inevitably forces some existing water out of the jar, however the jar remains as full as before. What you have are new alleles of water molecules forcing old ones out, while maintaining the overall number of alleles within the population of the water jar. As the new molecules are new alleles, and they have pushed out some old alleles of one type or another (but not necessarily all of one type) then it is quite conceivable that the amount of variation is increased.

When you have a speciation event, you do not divide all the alleles into either one population or the other such that no alleles are shared between the two daughter population, rather you divide the populations into two or more different groups that between them share almost all of the same alleles. Thus, even after ~6 million years of divergent evolution from our common ancestor with chimps we still share 95 to 98% of the DNA and alleles with these cousins.

Meanwhile, during those ~6 million years we see quite a divergence of hominid types and forms, representing a lot of new diversity.

Seems to me that evolution would have to work pretty hard to eliminate more variations than are created. To my mind there is a surfeit of new alleles that are routinely discarded because there is not enough room and opportunity to add more diversity to the existing matrix. The jar is full, so water overflows, rather than slowly drain away.

Enjoy.


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This message is a reply to:
 Message 1 by Faith, posted 03-25-2010 1:07 PM Faith has responded

Replies to this message:
 Message 85 by Faith, posted 03-27-2010 4:07 PM RAZD has responded

  
Faith
Member
Posts: 16206
Joined: 10-06-2001
Member Rating: 1.4


Message 22 of 851 (552004)
03-25-2010 6:58 PM


BREAK TIME FOR ME
I have to take a break here. I only got as far as nwr. There are some coming up I look forward to grappling with but overall I can see that the same arguments are going to continue to come up (and the general tone is losing its equanimity already. Sigh).

It makes perfect sense that this would happen of course but it's hard on my poor head, so I have to ask that further contributors to this thread PLEASE read ALL the posts before responding.

I know, you probably won't see this until it's too late, but Oh well.


    
Phage0070
Inactive Member


Message 23 of 851 (552005)
03-25-2010 7:04 PM
Reply to: Message 19 by Faith
03-25-2010 5:54 PM


Re:
Faith writes:

Being focused on a single mutant or allele means I'm focused on a single trait and tracing it through a number of generations...

This is where you lose *me*; if you are focusing on a single trait then how can you make broad claims about genetic variability? While that particular trait might beat out inferior alternative traits, it says nothing about the overall genetic variation of the population. Indeed, it does not even indicate that this superior trait will not in turn be replaced by a more beneficial mutation.

Faith writes:

All I can say is that EACH of these selected individuals, as long as its offspring remain "pure" and its line continues to stay selected, not sharing genes with the other selected individuals, will progressively lose genetic variability down the generations as its traits become established in those generations to the point of forming a new population.

This is where you go wrong. An individual descended from another individual does not lose genetic variability based on if its siblings reproduce or not. Each offspring is an imperfect copy based on the theme of the parent; the individual is not winnowing its own genetics through reproduction, the winnowing occurs through the possibility that it will not reproduce at all.

It appears that you think an organism capable of asexual reproduction, if followed down through several generations, would show a narrowing and refinement of beneficial traits.

I realize I might not be making my point very well, so I made graphics! The first is what I understand you are talking about, with the circles representing organisms descending in a tree, with the colors representing traits:


As each generation goes down certain traits are "selected" and the offspring lose genetic diversity. The problem is that this is a gross misunderstanding of what *actually* happens in evolution. Observe:

In this case each organism is based on the traits of its predecessors, but with minor modification. The "selection" comes in when an organism fails to reproduce; for instance if the third generation organism with the yellow quarter fails to reproduce, then the 4th generation population would lack the yellow trait. This acts as a selection pressure toward all the other colors, and away from yellow. However, even with the lack of the yellow trait the fourth generation will be more diverse than any of the previous generations.

Faith writes:

I did have to take this step by step because it was hard for me to follow, but now I think I can say that the problem here is that you are treating the number and variety of "grandchildren" as a collection rather than as a line of evolution.

That is exactly what I am saying, because evolution as you are describing it is incorrect. It does not exist.

Faith writes:

In your scenario, assuming the trend continues, you will continue to get new generations of genetically distinct individuals, some passing on their distinctions, some not, but in the end you're only going to have a bigger population of the same species with all its usual variation and variability scattered throughout.

As the trend continues the species would change, taking on beneficial traits as they crop up and are selected for. That is the fundamental process of evolution; what you are talking about is speciation which does require isolation for those traits to differ significantly enough to prevent interbreeding, but the concept remains the same. Even then, a smaller isolated population would continue in increasing genetic diversity with the beneficial modifications receiving positive selection pressure.


This message is a reply to:
 Message 19 by Faith, posted 03-25-2010 5:54 PM Faith has responded

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PaulK
Member
Posts: 10841
Joined: 01-10-2003
Member Rating: 1.3


Message 24 of 851 (552006)
03-25-2010 7:13 PM
Reply to: Message 20 by Faith
03-25-2010 6:47 PM


quote:

But the variation is rebuilt during succeeding generations.

I bolded that statement because I believe that is wishful thinking that is not borne out in reality. If this were true conservationists wouldn't be wringing their hands over the small numbers of salmon that get themselves up a tributary where undesirable reproductions bring undesirable traits to the fore along with extremely reduced genetic possibilities for further change; and there wouldn't be a club for the preservation of the cheetah. While all along in this discussion I am assuming for the sake of argument that useful mutations do occur at a rate that allows them to become the basis for selected traits, in reality this simply doesn't happen, as all too many conservationist scientists in the field ought to be able to testify.


I am afraid that you don't know what you are talking about. Severe bottlenecks cause serious problems. The species is liable to go extinct before genetic variation can recover - especially if the population remains low - and THAT is what the conservationists are worried about.

In fact the cheetah disproves your argument because its genetic variation IS recovering:

Dating the genetic bottleneck of the African cheetah (Abstract)


...the character of genetic diversity for two rapidly evolving DNA sequences, mitochondrial DNA and hypervariable minisatellite loci, was examined. Moderate levels of genetic diversity were observed for both of these indices in surveys of two cheetah subspecies...


Back calculation from the extent of accumulation of DNA diversity based on observed mutation rates for VNTR (variable number of tandem repeats) loci and mitochondrial DNA supports a hypothesis of an ancient Pleistocene bottleneck that rendered the cheetah depauperate in genetic variation for nuclear coding loci but would allow sufficient time for partial reconstitution of more rapidly evolving genomic DNA segments.

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 Message 20 by Faith, posted 03-25-2010 6:47 PM Faith has responded

Replies to this message:
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Blue Jay
Member (Idle past 67 days)
Posts: 2615
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 25 of 851 (552014)
03-25-2010 8:51 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


You don't have to kill them all!
Hi, Faith.

I'm honored to finally meet you(r words): I've heard so much about you. I think you've been missed here.

Faith writes:

It seems to be generally overlooked that for evolution to occur, alleles must be eliminated, thus reducing genetic diversity...

... There is no way to get a trait established in a population if alleles in competition with the allele for that trait are not eliminated.

Can you tell me the difference between your argument and the one in which humans can’t have evolved from apes because there are still apes around?

When you say, “established,” I think you mean “fixed.” A fixed trait is one that is present in all individuals in a population. And, there is no rule that dictates that any trait has to become fixed in a population. Evolution can proceed just fine without any trait having ever become fixed in any population.

Only in a minority of cases do we actually encounter a single allele that is clearly superior to all alternative alleles in the population. Certainly, we should expect that some alleles---maybe even most of the alleles--- should be outcompeted and gradually depleted into nothing, but there is no rule about how many alleles can persist in a population for any given amount of time.

Here is a good example: in the side-blotched lizard, different males employ three different mating strategies (loyal guardian, dominating bully and sneaky cheater), all of which have been determined to be driven (at least in part) by genetics, and no one of which is sufficiently superior that it totally crowds the others out of the gene pool.

Inferiority is not a death sentence. Nature is far too complex to think that any appreciable number of genes have a single “best” allele among the available options. Thus, we should expect a considerable measure of diversity to persist at a considerable number of loci in the genome.

-----

Faith writes:

If you start with twenty alleles in a population for one gene and one of them becomes crucial for a particular environment and therefore gets selected, either rapidly or slowly depending on the selection pressure, you will lose the other nineteen alleles as the one selected comes to determine this particular trait.

Then why is it that we actually see so much variation in genomes around the world?

It is only a minority of alleles that are ever “crucial” in any situation, so it is only a minority of cases that result in one allele competitively eliminating all the alternatives. Tolerance of variability in any given gene is the norm in the real world, Faith: that’s the whole reason we even see “alleles” at all.

Natural selection does not have to smite all the competitors, it just has to smite some of the competitors.

Edited by Bluejay, : "this" for "your"


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


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Replies to this message:
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nwr
Member
Posts: 5168
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 2.2


Message 26 of 851 (552015)
03-25-2010 9:14 PM
Reply to: Message 20 by Faith
03-25-2010 6:47 PM


Faith writes:
Yes, mutation increases variation (although I'd point out that it does so by replacing another probably quite viable allele, ...

That's a misunderstanding right there. Variation is a property of the population as a whole, not an individual. The mutation replaces another allele in an individual, but the chances are that the allele is still present in the population. So the result of the mutation is an increase in variation within the population.

Faith writes:
and according to the Wikipedia demonstration I linked, which I will link again here, genetic drift DOES reduce variation and variability.

I'd say that you are reading too much into that demonstration. It is giving an exaggerated example as an illustration. The complete removal of an allele in 5 generations of drift is improbable, even with a population size of only 20. With larger populations it is even more improbable. Generally, you would expect drift to show up as a slow change in frequency, rather than complete elimination. I'm not a biologist, but I think it is still controversial as to whether genetic drift is significant enough to even be important.

Faith writes:
I have to refer you to my answer to Paul K here. This isn't a simple addition/subtraction. The subtraction that is done by the selective and isolating processes (NS, drift, bottleneck etc.) actively GETS RID OF competing alleles for that trait.

Most traits are the result of a combined effect of many genes, rather than a single gene. The near elimination of particular combinations can still leave the same variation in the population, and for a species with sexual reproduction (or other ways that depend on meiosis), crossovers can recreate combinations that had been eliminated by selection. So the loss of competing alleles and of combinations of alleles will not be nearly as complete as you suppose.

Faith writes:
Of course under some circumstances in which the selected trait gets completely isolated from the mother population those many new traits may continue on in the greater population, but as far as the selected population goes, it will gain its new adapted phenotype THROUGH the loss of all the other alleles.

The case of complete isolation is where you do see a reduction in variation. But you won't see a complete elimination of variation, at least in sexually reproducing species, because crossovers can recreate combinations that were removed by the isolation. Moreover, empirical evidence shows variation building up over subsequent generations. So evolution does not stop at that point. The isolated population is in a precarious situation, and more likely to go extinct than the original group from which it was isolated. But if it survives long enough to build up more variation, it might become the founding group for a new species.

Faith writes:
nwr writes:
As far as I know, what is mostly noticed is that variation stays fairly constant.

In populations where evolution is not going on this is true. I believe that was the observation embodied in the Hardy-Weinberg principle.


Hardy-Weinberg is a theoretical principle when there are no mutations and there is no selection. That's not what I was referring to. Under ordinary conditions, I would expect the loss of variation due to selection to pretty much match the amount of new variation produced by mutations. Under conditions of severe selection pressure, I would expect a decline in the amount of variation. Under favorable conditions (very low selection pressure), I would expect an increase in the amount of variation. As far as I know, that is what is actually observed.

Faith writes:
nwr writes:
A bottle neck, such as caused by isolation of a small population, can result in reduced variation.

No doubt, it DOES, and severely reduced GENETIC variability too. Along with some very interesting phenotypes that may even qualify as new species.

nwr writes:
But the variation is rebuilt during succeeding generations.

I bolded that statement because I believe that is wishful thinking that is not borne out in reality. If this were true conservationists wouldn't be wringing their hands over the small numbers of salmon that get themselves up a tributary where undesirable reproductions bring undesirable traits to the fore along with extremely reduced genetic possibilities for further change; and there wouldn't be a club for the preservation of the cheetah.


There is concern for the cheetah for two reasons. Firstly, it is still in a precarious situation due to reduced variation. Secondly, it is under heavy selection pressure due to habitat destruction in Africa.

Likewise, the concern with the salmon is that they are still under heavy selection pressure due to overfishing and habitat destruction.

Under a more normal selection pressure, I would expect the variation to be recovered over a number of generations. Under the heavy selection pressure that exists in these cases, the risk of extinction is significant.

Faith writes:
The cheetah has lasted quite a long time without going extinct AND without acquiring one iota of variability.

I don't think we know that (particularly the "one iota" part). We have not been recording DNA variation for long enough.

We do have good reason to believe that the domestic dog is a result of selection - probably artificial selection by human populations. There is still plenty of variation such as allows further artificial selection to produce many different breeds.

I am as interested in the evidence as you are. If some of our biologist members can produce relevant evidence, that would be useful. It is almost certain that the experiment has been done with drosophila - that is, severe selection to reduce variation, and then observation of the increase in variation over future generations.

In any case, we do have natural experiments with antibiotic resistance arising in bacteria. It is pretty much expected now that any new antibiotic will, after a while, lead to bacteria that are resistant to that antibiotic.


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Capt Stormfield
Member
Posts: 177
From: Vancouver Island
Joined: 01-17-2009
Member Rating: 3.3


Message 27 of 851 (552016)
03-25-2010 9:24 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


It's a Forest, Not Just One Tree.
Am I missing something here, or is the essence of Faith's problem that in her attempt to cull one allele out of the herd she is forgetting that each generation of an organism has numerous mutations? While a population might be fixing the allele for a particular trait, and thus reducing the genetic variability in that population vis a vis that one trait, there are at the same time new alleles and new traits evolving which open up the potential for variation, selection, drift, and so on, regarding completely different aspects of the fitness of individuals in the population.

Capt.


This message is a reply to:
 Message 1 by Faith, posted 03-25-2010 1:07 PM Faith has responded

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Blue Jay
Member (Idle past 67 days)
Posts: 2615
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 28 of 851 (552021)
03-25-2010 10:28 PM
Reply to: Message 27 by Capt Stormfield
03-25-2010 9:24 PM


Re: It's a Forest, Not Just One Tree.
Hi, Capt Stormfield.

Capt Stormfield writes:

Am I missing something here, or is the essence of Faith's problem that in her attempt to cull one allele out of the herd she is forgetting that each generation of an organism has numerous mutations?

There are several different arguments that could be brought against Faith's argument as it stands. NWR hit a good one in distinguishing between genotype and phenotype, and I mentioned the "successional evolution" folly, and Paul argued the math.

I think that, in general, Faith is dealing in simple, absolute principles, which really is not an appropriate paradigm for evolutionary biology.

I thought about pointing out that the generational mutation rate for humans has recently been estimated at approximately 60/individual; and that this would require natural selection to be able to entirely eliminate more than 60 alleles that were already present in the population every time a new individual was born, in order for the genetic diversity in the population to actually decrease. At the time, I decided that there were easier ways of making my point, though.


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 27 by Capt Stormfield, posted 03-25-2010 9:24 PM Capt Stormfield has not yet responded

  
Coyote
Member
Posts: 4749
Joined: 01-12-2008
Member Rating: 1.5


Message 29 of 851 (552028)
03-26-2010 12:09 AM
Reply to: Message 27 by Capt Stormfield
03-25-2010 9:24 PM


Re: It's a Forest, Not Just One Tree.
Actually it is just one tree, not a forest.

The scientific evidence suggests a pattern of one tree (or bush), branching all the time, while the biblical concept of "kinds" requires a forest -- that is, each of the "kinds" is specially created and does not branch.

I suspect this is the root of this entire thread.

Once again I suspect we see the biblical view of creation trying to argue against the scientific evidence.


Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
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Dr Adequate
Member
Posts: 12839
Joined: 07-20-2006
Member Rating: 2.1


Message 30 of 851 (552029)
03-26-2010 12:10 AM
Reply to: Message 7 by Faith
03-25-2010 3:11 PM


Re: Not a simple addition and subtraction problem
If you start with twenty alleles in a population for one gene and one of them becomes crucial for a particular environment and therefore gets selected, either rapidly or slowly depending on the selection pressure, you will lose the other nineteen alleles as the one selected comes to determine this particular trait.

Well, if you had a magic wand that abolishes neutral variation, then I guess that is pretty much what would happen under those particular set of circumstances, if you waited long enough.

And if, on the other hand, you started with one allele and there were twenty different environments into each of which adaptive radiation can take place, such that different versions of that gene would be suited to different environments, then you'd end up with twenty different alleles, if you waited long enough.

What's your point?

Edited by Dr Adequate, : No reason given.


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