Evolution Requires Reduction in Genetic Diversity

Note that I did say that gene frequency and allele frequency are often used interchangeably. But you are either using it improperly or the paragraph I was responding to makes absolutely no sense. Inbreeding doesn't change the proportion of alleles but it does change the "gene/allele frequencies" ??? How does that make sense?So let me rephrase my comment about inbreeding...Inbreeding does not change the gene/allele frequencies what it does is change the genotypic frequencies.It takes selection or drift to change gene/allele frequencies.HBD

Consider this example: trochiloides is the ancestral species. Now imagine there are 10 mutations between trochiloides and ludlowi - not enough to cause infertility. There is also 10 mutations between trochiloides and obscuratus so they are able to hybridize freely as well. Also 10 mutations between ludlowi and viridanus and between obscuratus and plumbeitarsus, all able to freely hybridize.However, between viridanus and plumbeitarsus there are 40 total accumulated mutations. So, now the species on the extremes of the ring have significant differences and no longer can interbreed.If all you are doing is shuffling alleles around in different combinations, there is no basis for genetic incompatibility. If all the alleles existed in the original population and are simply being shuffled into new combinations, then all those alleles would be compatible because they would have all "seen" each other at one time in the original population. Arranging them in different combinations wouldn't result in incompatibility. Yes, what NoNukes was describing in your quote is more like selection. No. There are four primary evolutionary forces. Migration, Selection, Mutation, and Drift. Selection depends on fitness differentials, migration does not. ???? HBD

I suppose if you want to create your own definitions.Migration is the movement of individuals between populations. Migration is gene flow, it does not select anything, it moves genes between populations. It is not just movement of genes out of a population to form subpopulations but it also involves migration INTO populations. Genetic drift is more like "random selection" as you call it. It works by eliminating individuals in a population regardless of their genotypes or fitness. It most certainly does mean something, but no, fitness doesn't cause genetic change, selection acting on fitness causes genetic change. It can and has been demonstrated in the lab and in field experiments. But where is the evidence of this? These definitions have come about because of work done by biologists studying these processes. You are making up new definitions to accommodate your view; you can't define yourself into being right. Modes of speciation are fairly controversial in evolutionary biology. The major distinction is the amount of gene flow present between the main population and the subpopulation. Allopatric speciation has no gene flow because of a physical barrier. Peripatric has isolation of a subpopulation but no physical barrier so there is still potential for gene flow. In Parapatric the subpopulation is not isolated and there can still be gene flow between the main population and subpopulation. For Sympatric the subpopulation forms within the main population so there is potential for significant gene flow. So potential for gene flow is the key distinction between the modes of speciation.ABE: The question for the these different modes of speciation then becomes - how do you prevent or minimize migration (ie. gene flow) between the main population and the newly formed subpopulation? Allopatric makes sense - the physical barrier prevents migration, but for the others the answer is not so clear cut.HBDEdited by herebedragons, : No reason given.

Hypothetical, yes - for simplicity sake. Can't prove? well... Speciation by distance in a ring speciesAbstract:

quote:

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Ring species, which consist of two reproductively isolated forms connected by
a chain of intergrading populations, have often been described as examples of
speciation despite gene flow between populations, but this has never been
demonstrated. We used amplified fragment length polymorphism (AFLP)
markers to study gene flow in greenish warblers (Phylloscopus trochiloides).
These genetic markers show distinct differences between two reproductively
isolated forms but gradual change through the ring connecting these forms.
These findings provide the strongest evidence yet for ‘‘speciation by force of
distance’’ in the face of ongoing gene flow.

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Look this paper over and give me your critique. Of particular interest is Fig 2.Keep in mind this paper is a bit older and they seem to lean toward the sympatric or parapatric modes of speciation. More recent work has suggested that there probably was isolating barriers between populations at one time in their evolutionary history.HBD

I'm not sure how it seems Lamarkian... sort of anthropomorphic maybe, seeming as though these forces are acting purposefully. Right, fitness doesn't change genetic make up but selection does - acting upon the relative fitness of individuals.An important point to this discussion is how the various forces affect genetic diversity. Here is a table that helps explain it:

	Variation within subpopulation	Variation between subpopulations	Affect all loci
Mutation	increase	increase	No
Migration	increase	decrease	Yes
Drift	decrease	increase	Yes
Selection	increase/decrease*	increase/decrease*	No

(Adapted from: Conner and Hartl (2004). A primer of ecological genetics. Sinauer Associates)* Selection would most often tend to decrease variation except in cases such as heterozygote advantage were both homozygotes are being selected against in which case would tend to increase variation. I think the main point of contention, at least with creationists, is the idea of "survival of the fittest" which seems malevolent to them - especially when applied to humans. I don't particularly like the phrase myself as it misses the nuances of how selection and fitness actually work.HBD

Not at all. Gene flow would not be a yes or no answer but how much. What if you had two populations of 1,000 individuals and there was 1 migrant per year from each population that found its way to the other population. Would that be different from the situation where 100 individuals per year migrated? Of course it would. In which situation would it be more difficult for the two populations to differentiate? Message 571Natural selection is not the only factor involved; that's why we talk about drift, migration and mutation as well. I don't mean that researchers try to manipulate gene flow, but for two populations to differentiate enough to become distinct populations there needs to be reduced gene flow otherwise migration tends to reduce differentiation between populations. Not to a biologist. The question is why would gene flow be in only one direction? Why would a population emigrate to a region but there be no continued gene flow back and forth from the main population? Could it be that a physical barrier is important? If so, we already have a term for that type of situation - the founder effect. Why create a new term for a known phenomenon?Your whole argument rests on this one special case of migration, which has been well studied, but ignores other cases where there is not a founder effect. Or is your argument that the founder effect is the ONLY mode of speciation?HBD

If an individual migrates OUT of a population it moves INTO another population. If an individual moves INTO a population it has moved OUT of another population. You are only considering one population and one direction of gene flow. You need to keep the whole meta-population in mind. What you are trying to explain is how two subpopulations become different enough to be distinct populations that no longer interbreed. At first, they are both part of a larger meta-population. There are literally thousands of examples. You have been shown several, but you ignore them. The examples that fluctuate between morphs are more dramatic because you can "see" it happening. But there are plenty of examples were population shifts are clearly the result of natural selection. But I don't suppose you are up to reading up on them. Some concepts are difficult to understand and do take some explanation in order to grasp the concept. Like I started to bring up the Hardy-Weinberg equilibrium in a previous message but decided against it because I was afraid it would take too much explanation to get across the point of it so I left it out. However, it is a very important principle for understanding the concept of allele and genotypic frequency.Biologists (and lay persons) who take the time to study the concepts are not confused by them.HBD

You have probably noticed that the number of creationists that frequent these discussion boards has declined considerably. They seem to all have retreated to their own forums such as Evolution Fairytale Forum. I felt the same way as you do at one time and spent some time debating over there. The quality of debate is MUCH worse over there. Well, I would say the debate over evolution versus creation is pretty much done. There are a few creationist holdouts who are willing to engage evolutionists, but very few. Many of those are complete wack-jobs, at least Faith is not like that, she is actually a fairly decent debater despite the difficulties. And at this time, Faith is pretty much the only creationist that frequents this forum.I debate here to learn new things (either from others or from research I do to prepare a post) and to practice presenting arguments. "Results" don't concern me much.I would be interested in debating some things that are still fairly controversial in evolutionary biology, like sympatric speciation, but don't get much response on those more detailed types of discussions.HBD

I will have to come back to this later today. It may take a rather lengthy explanation.HBD

Not exactly. I am saying that inbreeding alone will not change the allele frequency, it will only change the genotypic frequency; shuffling the alleles into homozygotes. In order to change the allele frequency you need mutation, selection, drift or migration. Yes, if alleles are introduced into or removed from a population it will change genotypic frequency. But inbreeding doesn't do that. In order for this to happen, alleles need to be removed or added to the population. Inbreeding alone doesn't do that.---------That should clarify what my point was but I will go ahead and explain what inbreeding actually does just to make sure it is clear.For a population that is breeding completely at random we expect that the genotypic frequency will reach an equilibrium point according to Hardy-Weinberg (of course all this will assume that there is no mutation, selection, drift or migration since we are focusing on the effect of inbreeding). So if the frequency of allele 'A' is 0.5 and the frequency of allele 'a' is also 0.5 then the genotypic frequency will be 0.25 'AA', 0.50 'Aa' and 0.25 'aa'. As long as mating is random and there is no selection, mutation, drift or migration these frequencies will not change.Inbreeding is non-random mating where individuals are more likely to mate with a closely related individual than they would by chance. The most extreme version of this is selfing, where there is 100% chance that an individual with mate with a closely related genotype (itself). So here's what happens... start with the same genotypic frequencies as above

Start Freq	1st gen Cross	Resultant Freq	F1 Freq	2nd gen Cross	Resultant Freq	F2 Freq
'AA' (.25)	x 'AA'-->'AA' (1)	.25 x 1 = .25	.375	x 'AA'--> 'AA' (1)	.375 x 1 = .375	.438
	x 'Aa' --> 'AA' (.25)	.50 x .25 = .125	-----	x 'Aa' -->'AA' (.25)	.25 x .25 = .062	-----
'Aa' (.50)	x 'Aa' -->'Aa' (.50)	.50 x .50 = .25	.25	x 'Aa' -->'Aa' (.50)	.25 x .50 = .125	.125
	x 'Aa' -->'aa' (.25)	.25 x .25 = .125	-----	x 'Aa' -->'aa' (.25)	.25 x .25 = .062	-----
'aa' (.25)	x 'aa' -->'aa' (1)	.25 x 1 = .25	.375	x 'aa' -->'aa' (1)	.375 x 1 = .375	.438

Notes about table: 1) 1st and 2nd gen cross is the frequency of resultant offspring 2) Resultant Freq is the original (or F₁) times the offspring frequency. 3) F₁ or F₂ Freq combines frequency of homozygotes produced by 'Aa' x 'Aa' and homozygotic crosses.After just two generations of complete inbreeding the genotypic frequencies have changed to:
'aa' = .438
'Aa" = .125
'AA' = .438.Now let's figure out the allele frequencies.
'a' = .438 + (.125/2) = .50
'A' = .438 + (.125/2) = .50.So the allele frequencies have not changed but the genotypic frequencies have shifted from being 50% heterozygous to only 12.5% in just 2 generations.Thus, inbreeding alone does not change allele frequency, only shuffles the alleles into homozygotes. So, there is no reason to think that inbreeding can cause enough differentiation to prevent interfertility since the same genotypes existed in the original population, but now, the proportion of genotypes has now changed.HBD

So... I'm an idiot, again? Nice. Typical. Rather than address the arguments...HBD

I just did all that work in Message 598 to demonstrate what inbreeding actually does and how allele frequency doesn't change by inbreeding alone. I guess you need to explain to me how inbreeding can create new allele frequencies. All you have done so far is to say that it does but you don't know how.You apparently understand this so well, explain where my calculations of frequencies in Message 598 are wrong.HBD

What? You want to trade insults? Naw. I'll provide the discussion you can stick to insults.HBD

Yes, genetic drift would be a way to change allele frequency and it is especially efficient in small populations. The role inbreeding plays is it moves alleles into homozygotes and so individuals removed from the population at random are more likely to be homozygotic and thus two alleles are removed with the death of that individual. But really, the key in this effect is population size, not specifically inbreeding (although there is certainly more inbreeding in small populations than there is in large populations)Here is a figure that shows the results of an experiment using different population sizes of Tribolium beetles. (I lifted it from Rich, Bell and Wilson (1979) Genetic drift in small populations of Tribolium. Evolution 33:579-584. but you would need a JSTOR subscription to view the whole paper) Each population started with an equal proportion of alleles (b⁺ - 0.50) and only varied by the number of founding individuals. Notice the general upward trend of each population; that indicates that selection is acting to favor the b⁺ allele. Also notice the magnitude of fluctuations and the number of subpopulations that go to fixation is reduced as the population size increases.Therefore yes, your founding population would experience drift because of the small population size and allele frequency would change, probably rather rapidly, but this is a known effect (founder effect) not something new you came up with.So, I will echo a question NoNukes posed"Is this really the only scenario we need to consider in order to rule out or in evolution?"HBD

The reason a small population inbreeds is that the individuals in that population are more likely to breed with a close relative than random chance would expect because there is so few choices of mates. It becomes more difficult to find a mate that is not closely related.I suppose it is unfortunate that I had to get so technical about this from a such a simple comment I originally made; that inbreeding alone would not change allele frequency but requires drift, selection, mutation of migration. Absolutely not. Faith originally wanted to exclude other evolutionary factors and claim that in a founding population inbreeding alone was sufficient to explain the differentiation of the populations. That's how this line of argument got started. So, in order to examine how a particular factor effects population structure you need to exclude other factors. Highly likely. I try really hard to understand what she is talking about but I may be missing the mark sometimes. I was only demonstrating what inbreed itself does. I totally agree that under real world conditions, allelic frequency will be affected. I would be completely satisfied with a statement such as "inbreeding will cause the allelic frequency to shift." but not at the exclusion of the other evolutionary factors. It is not inbreeding itself that causes allelic frequency to change it is drift and selection. I got the impression that Faith wants to exclude those factors (she does because those are "evolutionary forces") - that's not OK. Often what seems like a simple and straight-forward comment turns into a big fiasco. Here's my original comment: It could have helped some had she responded to my Message 558 where I stated this again So I am not relying on allelic frequency to remain constant at all. I tried to avoid all the detailed technicalities, but sometimes feel forced into it when the simple, straight-forward point is called ridiculous.HBD