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"Inbreeding" vital mechanism of evolution

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My thoughts on evolution.

 

It occurred to me that unnatural selection is a vital part of evolution after reading that this is how the great variation of dog races are produced in some instance of their race history.

 

Its quite trivial to understand this because when a population is decreased so increases the chances of inbreeding. For this to work the population cant be to small as a whole. By this I mean as an example of populating a small isolated island, the population as a whole do have the gene pole to prevent irreversible defect generation but the population on the island will start to inbreed catapulting (as seen in dogs) the defect variation and with natural selection and incoming animals this would in time result in a new specie.

 

This means that unnatural selection acts like a rough but fast sculpture and natural selection as a slow fine tuner.

 

Defect generation in unnatural selection can also be seen as a defense mechanism to change the creature fast for it to adapt to the surroundings.

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Well, close...

 

The mechanism by which a small segment of the population becomes isolated *is* an important mechanism of evolution, called genetic bottleneck or founder effect depending upon whether it's caused by disaster or colonization of new habitat, repsectively.

 

And inbreeding probably *does* contribute to the fixation of alleles in populations in the circumstances you describe.

 

The problem is that inbreeding actually *decreases* what evolution has to play with, and would therefore be detrimental to the long-term survival of the population. It increases the chances of homozygosity at any one loci, meaning that evolution must wait for new mutations rather than acting on existing variation. It also causes homozygosity and fixation of alleles *without* regard to selective pressures, which is why you see so many lethal and barely sub-lethal birth defects in an inbred population.

 

Another consequence of the loss of heterozygosity that comes with inbreeding is the loss of diversity of alleles in the Major Histocompatability Complex, which plays a large role in the immune system. I'm not totally up to date on immunology, but I do recall it being established that the immune system requires as much diversity in these genes as possible, and loss of that diversity results in a weaker immune system.

 

In short, I don't think it's defensible to consider inbreeding adaptive or beneficial, even in the circumstances you describe. It *does* have an effect, especially in the situations described, but I'm not convinced it would be a positive one (or reliably enough so to be considered adaptive or beneficial).

 

Mokele

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Well' date=' close...

 

The mechanism by which a small segment of the population becomes isolated *is* an important mechanism of evolution, called genetic bottleneck or founder effect depending upon whether it's caused by disaster or colonization of new habitat, repsectively.

 

And inbreeding probably *does* contribute to the fixation of alleles in populations in the circumstances you describe.

 

The problem is that inbreeding actually *decreases* what evolution has to play with, and would therefore be detrimental to the long-term survival of the population. It increases the chances of homozygosity at any one loci, meaning that evolution must wait for new mutations rather than acting on existing variation. It also causes homozygosity and fixation of alleles *without* regard to selective pressures, which is why you see so many lethal and barely sub-lethal birth defects in an inbred population.

 

Another consequence of the loss of heterozygosity that comes with inbreeding is the loss of diversity of alleles in the Major Histocompatability Complex, which plays a large role in the immune system. I'm not totally up to date on immunology, but I do recall it being established that the immune system requires as much diversity in these genes as possible, and loss of that diversity results in a weaker immune system.

 

In short, I don't think it's defensible to consider inbreeding adaptive or beneficial, even in the circumstances you describe. It *does* have an effect, especially in the situations described, but I'm not convinced it would be a positive one (or reliably enough so to be considered adaptive or beneficial).

 

Mokele[/quote']

 

I'm not sure I fully understand you. It doesn't have to be "beneficial" in the long term to be part of evolutionary theory. By that I mean Its really not beneficial until the population decreases then it is a mathematical consequence. Then I wrote that animals not subjected to inbreeding would come to trough this bottleneck and bring diversity to the gene pool.

 

I think the lack of evidence of smooth transitions in the species variation suggests rapid evolvement which you get from unnatural selection in "analogy" with breeding new dog races.

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It doesn't have to be "beneficial" in the long term to be part of evolutionary theory. By that I mean Its really not beneficial until the population decreases then it is a mathematical consequence.

 

Oh, I agree that it doesn't have to be beneficial, and I agree that it does have a place in what happens during bottlenecks or founding of population. Mostly what I was disagreeing with was that it seems you were arguing that in some cases it could be beneficial, which I don't agree with. Statistically significant, yes, but not beneficial.

 

Then I wrote that animals not subjected to inbreeding would come to trough this bottleneck and bring diversity to the gene pool.

 

I'm unclear what you mean by this. Do you mean that new individuals would join the original, inbreed founder population?

 

I think the lack of evidence of smooth transitions in the species variation suggests rapid evolvement which you get from unnatural selection in "analogy" with breeding new dog races.

 

But inbreeding isn't *necessary* for these rapid changes, only a small population size, which can still mean several thousand individuals. While inbreeding can cause fast changes, it also makes them in a totally non-selective way that results in decreased fitness, since more the changes are negative than positive.

 

Basically, I see it a potential factor, but I'd also argue that any population for which it became a *major* factor would be *really* screwed in the long term. The fixation of so many negative traits and the loss of diversity would mean that the population would probably be outcompeted by the first non-inbred population to come along. After all, inbreeding has produced major and rapid changes in domestic dogs, but it's also produced animals whose eyeballs simply fall out or who can't stop drooling or whose hearts are so overstrained they typically die before middle-age.

 

Mokele

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Oh' date=' I agree that it doesn't have to be beneficial, and I agree that it does have a place in what happens during bottlenecks or founding of population. Mostly what I was disagreeing with was that it seems you were arguing that in some cases it could be beneficial, which I don't agree with. Statistically significant, yes, but not beneficial.

 

 

 

I'm unclear what you mean by this. Do you mean that new individuals would join the original, inbreed founder population?

 

 

 

 

 

But inbreeding isn't *necessary* for these rapid changes, only a small population size, which can still mean several thousand individuals. While inbreeding can cause fast changes, it also makes them in a totally non-selective way that results in decreased fitness, since more the changes are negative than positive.

 

Basically, I see it a potential factor, but I'd also argue that any population for which it became a *major* factor would be *really* screwed in the long term. The fixation of so many negative traits and the loss of diversity would mean that the population would probably be outcompeted by the first non-inbred population to come along. After all, inbreeding has produced major and rapid changes in domestic dogs, but it's also produced animals whose eyeballs simply fall out or who can't stop drooling or whose hearts are so overstrained they typically die before middle-age.

 

Mokele[/quote']

 

"I'm unclear what you mean by this. Do you mean that new individuals would join the original, inbreed founder population?"

 

Yes, for the population to survive in the long term. Also answering the last bit.

 

 

"But inbreeding isn't *necessary* for these rapid changes, only a small population size, which can still mean several thousand individuals. While inbreeding can cause fast changes, it also makes them in a totally non-selective way that results in decreased fitness, since more the changes are negative than positive."

 

Well these inbreeds are indeed selective since they abide by the same rules as those derived from natural selection. Fitness, reproduction success and so on. Understand that this is just an initial phase of evolution once the population is on its feet the chances of inbreeding is small then natural selection takes it from there.

 

As for the necessity, well natural selection is slow at best compared to unnatural selection and it's really based on the creature as a whole, what it comes down to is the survival of the specie then everything that works is beneficial.

 

"But inbreeding isn't *necessary* for these rapid changes, only a small population size, which can still mean several thousand individuals."

 

Well that is something I dont agree with. If there is a faster mechanism that works then that takes modus operandi.

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Well these inbreeds are indeed selective since they abide by the same rules as those derived from natural selection. Fitness, reproduction success and so on. Understand that this is just an initial phase of evolution once the population is on its feet the chances of inbreeding is small then natural selection takes it from there.

 

But the process of inbreeding itself is *not* selective. Inbreeding causes alleles to increase in frequency without regard to their positive or negative effects, but instead purely by chance. That's why inbred populations have so many more birth defects. And it's been experimentally demostrated that fitness is significantly lowered in inbred populations compared to non-inbred populations.

 

That's my point. It will affect gene frequency, yes, but in a random way, and *certainly* not in a selective way.

 

As for the necessity, well natural selection is slow at best compared to unnatural selection and it's really based on the creature as a whole, what it comes down to is the survival of the specie then everything that works is beneficial.

 

Natural selection is only slow in large populations with reduced genetic variation. The reason we got dog breeds so fast is because a) we've had tens of thousands of years to get them, b) canines are pretty geneticly variable anyway, especially when protected from normal selective pressures by living in captivity and most of all c) by "line-breeding" and breeding for specific traits, we are, in effect, imposing very strong selective pressure on a small population, resulting in rapid change.

 

In inbreeding of domestic dog breeds is not a mechanism of their overall change, but a side effect due to humans using unusually small and closely related populations to cause even more rapid change than usual. If we breed a dog for height, it's natural (or rather, artificial) selection that makes the population get taller over the years. If the population is inbred, that has nothing to do with the process of them getting taller, only the reason why they display numerous unrelated genetic defects, such as bad eyes, deafness, heart trouble, or gastro-intestinal ailments.

 

Intense selection on a small population is why dog breeds changed so fast, not inbreeding. Inbreeding just explains why they're so damn unhealthy and generally just screwed up.

 

Well that is something I dont agree with. If there is a faster mechanism that works then that takes modus operandi.

 

Just because it causes change faster doesn't mean it's what actually happens. Remember, the fast changes we see in punctuated equilibrium still take thousands and thousands of generations.

 

Inbreeding is not selective, and therefore cannot produce adaptation. Only natural selection can produce adaptation.

 

Also, "unnatural selection" is not the correct term for it.

 

Mokele

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The only way that inbreeding increases the rate of evolution for a specific population is to increase the chances of another bottleneck. It reduces genetic variability, as Mokele has said, and in the event of a drastic change in the population's environment, inbreeding makes it more likely that a large percentage of the population would die. For example, if an emerging disease makes contact with an inbred population, the genetic homogeneity will likely increase the number of individuals that die, causing a bottleneck. Inbreeding, like large meteors hitting the planet, can increase the rate of evolution, but it is in no sense beneficial for the extant organisms.

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My thoughts on evolution.

 

It occurred to me that unnatural selection is a vital part of evolution after reading that this is how the great variation of dog races are produced in some instance of their race history.

 

Its quite trivial to understand this because when a population is decreased so increases the chances of inbreeding. For this to work the population cant be to small as a whole. By this I mean as an example of populating a small isolated island, the population as a whole do have the gene pole to prevent irreversible defect generation but the population on the island will start to inbreed catapulting (as seen in dogs) the defect variation and with natural selection and incoming animals this would in time result in a new specie.

 

This means that unnatural selection acts like a rough but fast sculpture and natural selection as a slow fine tuner.

 

Defect generation in unnatural selection can also be seen as a defense mechanism to change the creature fast for it to adapt to the surroundings.

Inbreeding doesn't lead to defects being generated, but rather it increases the likelihood of existing recessive defective genes being homozygous in more individuals in the population, and thus being expressed phenotypically.

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But the process of inbreeding itself is *not* selective. Inbreeding causes alleles to increase in frequency without regard to their positive or negative effects' date=' but instead purely by chance. That's why inbred populations have so many more birth defects. And it's been experimentally demostrated that fitness is significantly lowered in inbred populations compared to non-inbred populations.

 

That's my point. It will affect gene frequency, yes, but in a random way, and *certainly* not in a selective way.

 

 

 

Natural selection is only slow in large populations with reduced genetic variation. The reason we got dog breeds so fast is because a) we've had tens of thousands of years to get them, b) canines are pretty geneticly variable anyway, especially when protected from normal selective pressures by living in captivity and most of all c) by "line-breeding" and breeding for specific traits, we are, in effect, imposing very strong selective pressure on a small population, resulting in rapid change.

 

In inbreeding of domestic dog breeds is not a mechanism of their overall change, but a side effect due to humans using unusually small and closely related populations to cause even more rapid change than usual. If we breed a dog for height, it's natural (or rather, artificial) selection that makes the population get taller over the years. If the population is inbred, that has nothing to do with the process of them getting taller, only the reason why they display numerous unrelated genetic defects, such as bad eyes, deafness, heart trouble, or gastro-intestinal ailments.

 

Intense selection on a small population is why dog breeds changed so fast, not inbreeding. Inbreeding just explains why they're so damn unhealthy and generally just screwed up.

 

 

 

Just because it causes change faster doesn't mean it's what actually happens. Remember, the fast changes we see in punctuated equilibrium still take thousands and thousands of generations.

 

Inbreeding is not selective, and therefore cannot produce adaptation. Only natural selection can produce adaptation.

 

Also, "unnatural selection" is not the correct term for it.

 

Mokele[/quote']

 

Instead of ensuring purity in inbreeding one could go from the abnormalities produced. Thereby get a new line of dogs that compared to its parents look like misfits. It are these misfits Im interested in. If by chanse one misfit got a superior trait it would manifast itself in the gene pool.

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Instead of ensuring purity in inbreeding one could go from the abnormalities produced. Thereby get a new line of dogs that compared to its parents look like misfits. It are these misfits Im interested in.

 

The misfits are just genetic variations, mutations that you're actually seeing because inbreeding makes them homozygous. That's not necessarily a good thing; many traits work best in heterozygous form.

 

If by chanse one misfit got a superior trait it would manifast itself in the gene pool.

 

Yes, but inbreeding causes increased homozygosity at *all* loci. Your misfit might be great at one thing, but chances are it has *more* than enough now-homozygous negative mutations to outweight the benefits of that one beneficial trait.

 

In experimental manipulations, inbreeding was found to cause a continual decline in fitness, because, as you probably know, negative mutations are more common, so if you make *everything* homozygous, you'll get more negative than positive.

 

Mokele

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The misfits are just genetic variations' date=' mutations that you're actually seeing because inbreeding makes them homozygous. That's not necessarily a good thing; many traits work best in heterozygous form.

 

 

 

 

Yes, but inbreeding causes increased homozygosity at *all* loci. Your misfit might be great at one thing, but chances are it has *more* than enough now-homozygous negative mutations to outweight the benefits of that one beneficial trait.

 

 

 

 

In experimental manipulations, inbreeding was found to cause a continual decline in fitness, because, as you probably know, negative mutations are more common, so if you make *everything* homozygous, you'll get more negative than positive.

 

 

 

Mokele[/quote']

 

I already told you the premises, the trait would have to be superior.

 

Well evolution takes time and the misfit is subjected to the surroundings so this takes care of the chances that this misfit would have genetic makeup that in overall would mean a success of breeding. Also the selective event to which the population gets isolated or decreased in the event the outcome genetic makeup is different would ensure genetic makeup to be strong/good. Inbreeding would then strengthen these good traits.

 

I never wrote that inbreeding would be beneficial in the long term and that the scenario i described would mean irreversible inbreeding. I doubt that the experiment would have the same selective pressure than in the real world and you cant make any conclusion to its possible beneficial mechanism in all its possible events that this happens.

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But the process of inbreeding itself is *not* selective. Inbreeding causes alleles to increase in frequency without regard to their positive or negative effects, but instead purely by chance. That's why inbred populations have so many more birth defects.

 

I dont get this bit :confused:

 

surely breeding, be it in or out, is selective by its very nature? ie, alleles will get shuffled about and put in different combinations, and the combinations with (overall) the best alleles has the highest chance of passing on those alleles, reguardless of the fact that your mother might also be your brother?

 

Also, i thought the higher birth defects were due to resesively deleteriouse mutations, which are likely to be shared by bro' and sis', and so the progeny of insest are more likely to be homologouse for resessive bad genes; rather than the random inheritance doobries you mentioned above?

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I already told you the premises, the trait would have to be superior.

 

Yes, I understand. My point is that while that particular trait may be superior, the process of inbreeding will bring out so many other traits, mostly bad, that the *cummulative* effect of the animal's fitness with be a decrease.

 

Well evolution takes time and the misfit is subjected to the surroundings so this takes care of the chances that this misfit would have genetic makeup that in overall would mean a success of breeding. Also the selective event to which the population gets isolated or decreased in the event the outcome genetic makeup is different would ensure genetic makeup to be strong/good. Inbreeding would then strengthen these good traits.

 

But population bottlenecks and founder effect are *rarely* selective, so your small population would not have all good traits.

 

On top of this, even if it *was*, many damaging mutations could be hiding in recessive form (and since selection acts only of phenotype, they could not be totally weeded out). These hidden deleterious traits would be exposed via inbreeding and increased in frequency. This would *damage* the otherwise strong population.

 

I doubt that the experiment would have the same selective pressure than in the real world and you cant make any conclusion to its possible beneficial mechanism in all its possible events that this happens.

 

The experiment I described, with birds, was actually done in the wild, IIRC, so they were exposed to natural selection pressures.

 

As for drawing conclusions, I'm not saying it can *never* be beneficial. It is possible, just very, very unlikely. My point (overall) is that it probably has either a) no detectable effect compared to other factors like selection and founder effect or b) has a negative effect in so many cases that positive effects should be considered an anomaly, not a mechanism of evolution.

 

surely breeding, be it in or out, is selective by its very nature? ie, alleles will get shuffled about and put in different combinations, and the combinations with (overall) the best alleles has the highest chance of passing on those alleles, reguardless of the fact that your mother might also be your brother?

 

Breeding of any sort is randomly assortive, but is not selective. In the bit above, you describe two things: the reproduction and the action of natural selection on the offspring. The selective part is the latter, the former is non-selective (aside from the usual competition for mates).

 

Basically, say Bob is heterogyzous for a lethal disease allele. When Bob breeds, there is a 50% chance of the kid getting the bad allele, and 50% chance of the kid getting the good one. In short, the process of gametogenesis and fertilization do not distinguish between "good" and "bad" genes, and are therefore not selective. Once the kid is born, then it is exposed to natural selection, which can weed out or keep those genes.

 

Also, i thought the higher birth defects were due to resesively deleteriouse mutations, which are likely to be shared by bro' and sis', and so the progeny of insest are more likely to be homologouse for resessive bad genes; rather than the random inheritance doobries you mentioned above?

 

You're right, we're just talking past each other, at different levels. The likelyhood of borthers and sisters sharing genes *is* increased, so if they mate together (rather than with non-siblings), they will be more likely to produce of a homozygote. For recessive lethal genes, this means more likihood of birth defects, but this applys across the board - because brothers and sisters are more likely to share the same allele at *all* loci, there is an increase in homozygosity at *all* loci in the inbred population over time. The birth defects are simply the "flag" that this declining heterozygosity is occuring. And, of course, because gametes don't assort by the selective effect of their genes, which trait becomes fixed is pretty much random.

 

Mokele

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"On top of this, even if it *was*, many damaging mutations could be hiding in recessive form (and since selection acts only of phenotype, they could not be totally weeded out). These hidden deleterious traits would be exposed via inbreeding and increased in frequency. This would *damage* the otherwise strong population."

 

First of all I'm talking about a degree of inbreeding which would occur in a "small" population not necessarily meaning very close relatives and not to the extent they become semi clones. As the mechanism of inbreeding would mean breeding of in this case animals of close genetic makeup and I'm not refuting the side affects of long term inbreeding.

 

Since obtaining energy is one of the primely important tasks for breeding and living, evolution result would abide by the rules of energy conservation. Dying of genetic "disorder" is then selective and breeding would then also be selective in the case of inbreeding.

 

An event where which energy becomes scarce to find in a particular area would then be very selective since the animals would compete over the same energy resources and at the same time the total population would decline making the chances for inbreeding higher. Since we are dealing with two individuals the chances are not low of some degree of inbreeding since both parties want offspring and the genetically important trait that is proven to gather more energy in that specific environment be of similar kind.

 

Tough bad traits would emerge the important thing is that good traits are strengthened and in my scenario there will be outcrossing, hybridization and together with natural selection and as good traits are spread to the non inbreeding population more and more animals would be able to survive in the new environment and consequently come and live there.

 

 

I do think new species are anomalies based on random events but confined to rules of evolution.

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The problem is that inbreeding caused homozygosity at *all* loci. Distant inbreeding does so more slowly, but eventually it will too.

 

Even with selective pressures, the problem of damaging mutations becoming too frequent doesn't go away, because selection acts on the organism, not the gene, and all the genes are "in it together".

 

For instance, say we have two individuals of a super-simplified hypothetical species with 4 genes, called 1, 2, 3, and 4. Individual A has a negative trait expressed at gene 1, and all others are good. Indivuidual B has a negative trait expressed at gene 3, but all others are good. Both have good and bad traits. Obviously, if selection weeds out both, it's moot because the imaginary species is extinct. If it weeds out neither, it's not really selecting anything. And if it weeds out one, the genetic flaws of the other will be propagated.

 

Selection can mitigate the results on inbreeding, I agree, but not entirely.

 

I'm not really sure I see much point in inbreeding as a significant mechanism. Chance alone means that any trait will eventually be expressed in homozygous form, and then selection can take it from there. Considering that you're including outcrossing, selection, and hybridization in your scenario, I'm not sure inbreeding would generate a detectable result. It might happen, but just be statistically insignificant.

 

Mokele

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The problem is that inbreeding caused homozygosity at *all* loci. Distant inbreeding does so more slowly' date=' but eventually it will too.

 

Even with selective pressures, the problem of damaging mutations becoming too frequent doesn't go away, because selection acts on the organism, not the gene, and all the genes are "in it together".

 

For instance, say we have two individuals of a super-simplified hypothetical species with 4 genes, called 1, 2, 3, and 4. Individual A has a negative trait expressed at gene 1, and all others are good. Indivuidual B has a negative trait expressed at gene 3, but all others are good. Both have good and bad traits. Obviously, if selection weeds out both, it's moot because the imaginary species is extinct. If it weeds out neither, it's not really selecting anything. And if it weeds out one, the genetic flaws of the other will be propagated.

 

Selection can mitigate the results on inbreeding, I agree, but not entirely.

[/quote']

 

I'm not sure how you derived "homozygosity at *all* loci" in my scenario and how you define inbreeding since the degree of inbreeding would first increase and then decline in the smaller population.

 

I'm not really sure I see much point in inbreeding as a significant mechanism. Chance alone means that any trait will eventually be expressed in homozygous form' date=' and then selection can take it from there. Considering that you're including outcrossing, selection, and hybridization in your scenario, I'm not sure inbreeding would generate a detectable result. It might happen, but just be statistically insignificant.

 

Mokele[/quote']

 

Are you meaning that somewhat inbreed population with a superior trait wont leave an imprint on the total population as a whole? I find that hard to belive since natural selection would do just that, and it doesn't know you came from a somewhat inbreed population.

 

My point is that inbreeding captures the random events in a larger scale (time for it to propagate) meaning faster evolution on the population as a whole.

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I'm not sure how you derived "homozygosity at *all* loci" in my scenario and how you define inbreeding since the degree of inbreeding would first increase and then decline in the smaller population.

 

Inbreeding means mating with one's self (selfing, usually restricted to plants and some inverts) or close relatives. As for homozygosity at all loci, this is simply what inbreeding does. Because you are breeding with individuals who are more likely than usual to share your alleles at any given locus, you are more likely to get homozygotes (including for rare alleles). Because all loci (or at the least all chromosomes) segreate independently, this applies to all of them.

 

For a better explanation than I can give, go here: http://www.amazon.com/exec/obidos/tg/detail/-/1405103450/qid=1127342680/sr=8-5/ref=pd_bbs_5/103-0010775-6196666?v=glance&s=books&n=507846

and search inside the book for "inbreeding". He certainly explains it better than I could.

 

Are you meaning that somewhat inbreed population with a superior trait wont leave an imprint on the total population as a whole? I find that hard to belive since natural selection would do just that, and it doesn't know you came from a somewhat inbreed population.

 

Perhaps I should rephrase. Because natural selection is involved, as well as some form of genetic bottleneck, it would be very difficult to discern after the fact (in established species) to what degree any inbreeding happened. You'd basically have to "catch it in the act" so to speak.

 

On top of that, I'm not sure it would work at all. Because you have a population suffering from the "double-whammy" of a genetic bottleneck, then inbreeding, genetic variability will be very low. Even though the inbreeding intensity would decrease over time, it would be a *long* time before any population could recover, geneticly, from that, and in the meantime they'd be at high risk of extinction. The parasites and pathogens would have a field day on/in the species.

 

As for your proposed mechanism to avoid this, a second group later for outcrossing, I suspect the second group would simply outcompete and replace the inbred group. Even if the inbred individuals had some wonderful mutation, they'd also be chock-full of damaging mutations, more than enough of those to drag down the fitness value to well below the level that even that advantageous mutation can counteract. This has been verified experimentally: inbred individuals have lower average fitness.

 

So basically, if totally isolated, they'd be a genetic leper colony and might drop dead from a light breeze. If more individuals arrive, the inbred animals would be outcompeted. I'm not really seeing it being a huge mechanism in either case.

 

My point is that inbreeding captures the random events in a larger scale (time for it to propagate) meaning faster evolution on the population as a whole.

 

And my point is that the process is so damaging that any beneficial traits brought to the forefront will be massively outweighed by deleterious traits also brought to the forefront, resulting in *lower* fitness, not higher. It'd be a fast ride down a dead end.

 

Mokele

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Inbreeding means mating with one's self (selfing' date=' usually restricted to plants and some inverts) or close relatives. As for homozygosity at all loci, this is simply what inbreeding does. Because you are breeding with individuals who are more likely than usual to share your alleles at any given locus, you are more likely to get homozygotes (including for rare alleles). Because all loci (or at the least all chromosomes) segreate independently, this applies to all of them.

 

For a better explanation than I can give, go here: http://www.amazon.com/exec/obidos/tg/detail/-/1405103450/qid=1127342680/sr=8-5/ref=pd_bbs_5/103-0010775-6196666?v=glance&s=books&n=507846

and search inside the book for "inbreeding". He certainly explains it better than I could.

[/quote']

 

Well the definition I've read is that inbreeding is that of mating with close genetically similar organisms. Then there will be a degree of inbreeding effect due to the degree of "close".

 

Perhaps I should rephrase. Because natural selection is involved' date=' as well as some form of genetic bottleneck, it would be very difficult to discern after the fact (in established species) to what degree any inbreeding happened. You'd basically have to "catch it in the act" so to speak.

[/quote']

 

Since the population is small the chance of a degree of inbreeding is pretty high. Then it is a vital mechanism of evolution since a degree of inbreeding would have affected the history of evolution. Since we want to come to an understanding why certain traits have emerged to become more frequent we have to take a degree of inbreeding into account. I'm certain a degree of inbreeding have effected human kind as well.

 

On top of that' date=' I'm not sure it would work at all. Because you have a population suffering from the "double-whammy" of a genetic bottleneck, then inbreeding, genetic variability will be very low. Even though the inbreeding intensity would decrease over time, it would be a *long* time before any population could recover, geneticly, from that, and in the meantime they'd be at high risk of extinction. The parasites and pathogens would have a field day on/in the species.

[/quote']

 

From then event explanation I wrote this would be a kind of a founder effect certainly not an extreme bottleneck.

 

As for your proposed mechanism to avoid this' date=' a second group later for outcrossing, I suspect the second group would simply outcompete and replace the inbred group. Even if the inbred individuals had some wonderful mutation, they'd also be chock-full of damaging mutations, more than enough of those to drag down the fitness value to well below the level that even that advantageous mutation can counteract. This has been verified experimentally: inbred individuals have lower average fitness.

[/quote']

 

Well, the most inbreed individuals would certainly be replaced in the long run due to damaging side affects. However for the lasting population to survive in that specific environment with a low degree of inbreeding they would have to have the specific trait derived from the smaller population in the beginning of the process. Since behavior *patterns* is due to the genetic makeup the chances are not low that individuals with a lower degree of inbreeding would return to that specific area. There is to be dynamic interaction back and forth between the population that has a higher degree of inbreeding and those larger populations.

 

So basically' date=' if totally isolated, they'd be a genetic leper colony and might drop dead from a light breeze. If more individuals arrive, the inbred animals would be outcompeted. I'm not really seeing it being a huge mechanism in either case.

[/quote']

 

On the contrary its not be totally isolated. This a would be a repeating process until the specific trait is emerged and successfully repeated. Since it would be repeating itself until the specific trait is emerged. By this I mean there have to be causes to the new trait and population cant survive there with a low degree of inbreeding had it not been for the specific trait. Hence the area would no longer be a kind of "bottleneck" were which the chances of inbreeding is high.

 

And my point is that the process is so damaging that any beneficial traits brought to the forefront will be massively outweighed by deleterious traits also brought to the forefront' date=' resulting in *lower* fitness, not higher. It'd be a fast ride down a dead end.

 

Mokele[/quote']

 

It wouldn't be a fast ride to a dead end nor a resulting dead end. Had not several populations existed outside the area were which the specific trait would have emerge then chances are that the animal would not survive at all in that environment since it would have to be a repeating process.

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Also since it is a repeating process the number of tries would end up in a process where which the superior trait would emerge quite rapidly in that specific time period together with a insignificant degree of fitness reduction. As to say the overall success of breeding and living would be higher than those without the trait.

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Well the definition I've read is that inbreeding is that of mating with close genetically similar organisms. Then there will be a degree of inbreeding effect due to the degree of "close".

 

That's precisely what I (and the book in the link) said.

 

Since the population is small the chance of a degree of inbreeding is pretty high. Then it is a vital mechanism of evolution since a degree of inbreeding would have affected the history of evolution. Since we want to come to an understanding why certain traits have emerged to become more frequent we have to take a degree of inbreeding into account. I'm certain a degree of inbreeding have effected human kind as well.

 

And you're certain based on what? I've already shown how your theory both has major weaknesses and would be difficult to test. Without empirical evidence, how can you be certain of anything?

 

Plus, as I pointed out, I highly doubt that species for which inbreeding was a mjaor component of their early speciation would survive at all.

 

From then event explanation I wrote this would be a kind of a founder effect certainly not an extreme bottleneck.

 

Then how if inbreeding going to be significant?

 

Seriously do the math and look at the inbreeding coefficents. They drop off *very* fast, so unless you have a *tiny* population, there will be no detectable effects. In fact, I'd estimate that any population of more than 100 would show *none*.

 

Well, the most inbreed individuals would certainly be replaced in the long run due to damaging side affects. However for the lasting population to survive in that specific environment with a low degree of inbreeding they would have to have the specific trait derived from the smaller population in the beginning of the process.

 

If the colonizing population bred with the original inbred population *at all*, which is far from a given, since these inbred, sickly, weakened freaks will not make desirable mates.

 

And even if they *do*, the offspring on an inbred and a normal will be weaker on average than normal + normal, so selection will eventually remove all traces of them from the gene pool.

 

Since behavior *patterns* is due to the genetic makeup the chances are not low that individuals with a lower degree of inbreeding would return to that specific area. There is to be dynamic interaction back and forth between the population that has a higher degree of inbreeding and those larger populations.

 

Only for certain species in certain situations. That's a pretty weak-ass mechanism if it can only apply in highly restricted scenarios.

 

On the contrary its not be totally isolated. This a would be a repeating process until the specific trait is emerged and successfully repeated. Since it would be repeating itself until the specific trait is emerged. By this I mean there have to be causes to the new trait and population cant survive there with a low degree of inbreeding had it not been for the specific trait. Hence the area would no longer be a kind of "bottleneck" were which the chances of inbreeding is high.

 

1) evolution is not goal-directed. It just happens. If there aren't enough colonizations for your scenario, too bad, evolution will work with what it has. If the gene flow is too high for inbreeding to be detectable or significant, again, too bad. I'm not seeing any sort of broad applicability for this.

 

2) Your description of this scenario is, frankly, piss-poor. If you aren't a native english speaker, that might explain it, but as it stands, your poor grammar and wording are preventing me from forming any consistent picture of the scenario you envision (if there is such a consistent picture).

 

Had not several populations existed outside the area were which the specific trait would have emerge then chances are that the animal would not survive at all in that environment since it would have to be a repeating process.

 

1) This does not in any way refute my point, so far as I can see, but...

 

2) It's so poorly written that I can barely make out what you're trying to say.

 

Mokele

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Inbreeding could confere a few benefits. for example, inbreeding would increase homology at gene loci, which could confer a higher tolerance for resessively-fatal mutations, and therefore allow a higher rate of mutation, possibly allowing the faster aquisition of new beneficial mutations.

 

A species adapted to inbreed could find itself with a higher reproduction rate due to the fact that finding a mate is easyer, due to not having to go to the trouble of finding a mate that is unrelated

 

a species adapted to (and able to survive the downsides of) inbreeding could find itself better able to survive bottlenecks; perhaps useful in unstable habitats, where the population could fluctuate wildly

 

maintanance of a good set of alleles: if a very good combination of alleles is achieved, inbreeding could resist the effect of natural selection to split the alleles up; in other words, inbreeding could lower diversity, which would be a good thing if the average set of alleles was pretty good.

 

and, of course, the chances of passing on your genes is increased by mating with someone genetically similar.

 

wether those would be enough to counteract the disadvantages of inbreeding...

 

most of those ^ advantages, by the way, were based some hypothetical advantages to partheneogenesis 1, which, being analogouse to the mating between two identical twins, could be considered uber-inbreeding.

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Actually, you're right about the advantages, and every time you see a bee hive, you see proof you're right. Most eusocial (hive) insects inbreed pretty badly, yet are very successful.

 

However, they "cheat". They're haplodiploid, meaning that diploid, fertilized eggs are females and haploid, unfertilized eggs are males. Because males have only one set of chromosomes, they cannot conceal any damaging mutations in the recessive state: every allele they have is fully expressed. This lets the population weed deleterious mutations out much faster than one would ever find in an entirely diploid species.

 

The advantages also apply to parthenogenic species too, but the catch this time is less fun: Most (possibly all) parthenogenic species are hybrids of two existing species. In spite of their advantages, they enjoy only modest success, and, importantly, most are only a few million years old. If you consider that inter-species hybirdization is probably not a new phenomenon, that brings up the question of where the older, probably similarly parthenogenic hybrid species are. The most probable answer is, of course, dead, and while this doesn't *prove* it's a Bad Thing, it does at least make it look very possible that it's not all it seems to be.

 

The problem is that, unless you have haplodiploidy to purge recessive lethal mutations from the gene pool, they'll begin accumulating. Even if we start with a hypothetical inbred population that's all homozygous for all good stuff, mutations happen fairly frequently (4 that affect final protien structure per generation in humans). While in a non-inbred population, a new mutation would basically be stuck in heterozygous form for a *long* time (and would probably simply vanish by genetic drift more often than not before ever being expressed), it would quickly find itself expressed in an inbred line, and could very quickly rise in gene frequency.

 

Evidently, since parthenogenic species *do* exist, the advantages of parthenogenesis can offset the detrimental effects for a while, but the question is, how long?

 

Mokele

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^ just to add to that, whilst i was looking into parthoneogenesis, i discovered that most parthaneogenisising (?) vertebrates live, sparsly distributed, in habitats where the chanses of bumping into a mate are quite slim.

 

more common is 'facultive partheneogenesis', whereby the individual can reproduse sexually or by partheneogenesis.

 

in those cases, sexual reproduction is usually chosen if a mate is available, and partheneogenesis is only chosen when mates are unavailable; which would seem to supporting the idea that inbreeding is, over the long term, unsustainable.

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That's precisely what I (and the book in the link) said.

 

 

 

And you're certain based on what? I've already shown how your theory both has major weaknesses and would be difficult to test. Without empirical evidence' date=' how can you be certain of anything?

 

Plus, as I pointed out, I highly doubt that species for which inbreeding was a mjaor component of their early speciation would survive at all.

 

Mokele[/quote']

 

Then I wonder if inbreeding hadn't been a part of the evolutionary *history* then why do avoiding inbreeding seem to be a behavior pattern thus being genetical information. Even if this means that those that inbreed eventually will die it still changes the overall genetic makeup so that this behavior is not to be repeated. The behavior pattern to avoid this will also be strengthened.

 

Also your insults are futile since I'm not native in English.

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Then I wonder if inbreeding hadn't been a part of the evolutionary *history* then why do avoiding inbreeding seem to be a behavior pattern thus being genetical information.

 

I'm not saying it never occurs, only that it's not a good thing and I don't think the role it plays in speciation is either good or significant. In fact, my position easily explains why the aversion to inbreeding is common: because lineages that lacked the aversion died.

 

Also your insults are futile since I'm not native in English.

 

I didn't mean to be insulting, but I am getting rather frustrated, as the discussion seems to be going in circles.

 

Mokele

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