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Author Topic:   What prevents micro evolution from becoming macro evolution
frako
Member
Posts: 2813
From: slovenija
Joined: 09-04-2010


Message 16 of 25 (590416)
11-08-2010 5:18 AM
Reply to: Message 15 by Dr Jack
11-08-2010 5:14 AM


there is good reason to think that the description of macroevolutionary patterns of evolution needs additional mechanisms.

why?
and what additional mechanisms?


This message is a reply to:
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Taq
Member
Posts: 7864
Joined: 03-06-2009
Member Rating: 4.3


Message 17 of 25 (590501)
11-08-2010 1:31 PM
Reply to: Message 10 by Coyote
11-07-2010 7:27 PM


Re: Creationists meltdown?
Creationists seem to have focused on "genetic meltdown" and "genetic entropy" lately.

Is there any evidence that these actually occur in normal populations?

This effect will be most pronounced in asexual populations due to the fact that they are not able to swap out negative alleles with neutral alleles through sexual recombination. The effect in pop gen circles is called "Muller's Ratchet". The evidence suggests that populations can only withstand a set number of slightly deleterious mutations. When you exceed this threshold these mutations are heavily selected against. In the abstract below, this is seen as a decrease in substitution over time due to stronger selection against new mutations.

quote:
PLoS One. 2009;4(3):e4969. Epub 2009 Mar 23.

Mutational meltdown in primary endosymbionts: selection limits Muller's ratchet.
Allen JM, Light JE, Perotti MA, Braig HR, Reed DL.

Zoology Department and Florida Museum of Natural History, University of Florida, Gainesville, Florida, USA. juliema@ufl.edu

Abstract
BACKGROUND: Primary bacterial endosymbionts of insects (p-endosymbionts) are thought to be undergoing the process of Muller's ratchet where they accrue slightly deleterious mutations due to genetic drift in small populations with negligible recombination rates. If this process were to go unchecked over time, theory predicts mutational meltdown and eventual extinction. Although genome degradation is common among p-endosymbionts, we do not observe widespread p-endosymbiont extinction, suggesting that Muller's ratchet may be slowed or even stopped over time. For example, selection may act to slow the effects of Muller's ratchet by removing slightly deleterious mutations before they go to fixation thereby causing a decrease in nucleotide substitutions rates in older p-endosymbiont lineages.

METHODOLOGY/PRINCIPAL FINDINGS: To determine whether selection is slowing the effects of Muller's ratchet, we determined the age of the Candidatus Riesia/sucking louse assemblage and analyzed the nucleotide substitution rates of several p-endosymbiont lineages that differ in the length of time that they have been associated with their insect hosts. We find that Riesia is the youngest p-endosymbiont known to date, and has been associated with its louse hosts for only 13-25 My. Further, it is the fastest evolving p-endosymbiont with substitution rates of 19-34% per 50 My. When comparing Riesia to other insect p-endosymbionts, we find that nucleotide substitution rates decrease dramatically as the age of endosymbiosis increases.

CONCLUSIONS/SIGNIFICANCE: A decrease in nucleotide substitution rates over time suggests that selection may be limiting the effects of Muller's ratchet by removing individuals with the highest mutational loads and decreasing the rate at which new mutations become fixed. This countering effect of selection could slow the overall rate of endosymbiont extinction.
http://www.ncbi.nlm.nih.gov/pubmed/19305500



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Taq
Member
Posts: 7864
Joined: 03-06-2009
Member Rating: 4.3


Message 18 of 25 (590505)
11-08-2010 1:37 PM
Reply to: Message 3 by slevesque
11-07-2010 5:06 PM


- Neo-Darwinian evolutionists will say that these will accumulate to the point that new features, organs, etc. will appear in the population, showing an ever evolving and changing trend in biological populations. This is what they will cal macro-evolution.

Macroevolution does not require the production of new organs. Even "new organs or features" is a misnomer since evolution is descent with MODIFICATION, not evolution of something completely new. For example, the legs of tetrapods are modified fins, not something completely new.

What macroevolution requires is the production of new species. For example, chimps and humans are separate species but no new organs or features had to evolve.

- Creationists will say that these will accumulate to the point that the mutational burden will become much too high, and this will lead the population down a spiralling path to genetic meltdown. Macro-evolution will therefore never happen.

The millions of mutations that separate chimps and humans did not result in non-viable species, so obviously this burden has not occurred yet since chimps and humans shared a common ancestor.

Creationist will often complain when evolutionist use examples of micro-evolution to prove that macro-evolution will happen, because it simply does not discard the possibility that accumulating mutations could lead to genetic meltdown.

Creationists need to move beyond "possibility". They need to show that it is an unavoidable consequence. They have failed to do so.


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Coyote
Member (Idle past 269 days)
Posts: 6117
Joined: 01-12-2008


Message 19 of 25 (590506)
11-08-2010 1:38 PM
Reply to: Message 17 by Taq
11-08-2010 1:31 PM


Re: Creationists meltdown?
If I am reading that correctly, there is a mechanism that limits the effects of genetic entropy?

Is that how you read it?


Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
This message is a reply to:
 Message 17 by Taq, posted 11-08-2010 1:31 PM Taq has responded

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Taq
Member
Posts: 7864
Joined: 03-06-2009
Member Rating: 4.3


Message 20 of 25 (590511)
11-08-2010 2:03 PM
Reply to: Message 19 by Coyote
11-08-2010 1:38 PM


Re: Creationists meltdown?
If I am reading that correctly, there is a mechanism that limits the effects of genetic entropy?
Is that how you read it?

Yes, and that mechanism is natural selection. By comparing the same endosymbiont across several lineages you can determine the substitution rate (i.e. fixed mutation rate) over time. The substitution rate decreases over time indicating that more and more mutations were selected against over time. The strongest candidate for negative selection is deleterious mutations.

The creationist model assumes stead accumulation of deleterious mutations across the entire population, but the evidence in the paper above argues against that. The evidence suggests that the population only carries a certain amount of deleterious mutations, and that any additional deleterious mutations that occur are selected against and do not spread in the population like the slightly deleterious mutations that occurred before them.


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 Message 21 by Coyote, posted 11-08-2010 2:34 PM Taq has responded

  
Coyote
Member (Idle past 269 days)
Posts: 6117
Joined: 01-12-2008


Message 21 of 25 (590513)
11-08-2010 2:34 PM
Reply to: Message 20 by Taq
11-08-2010 2:03 PM


Re: Creationists meltdown?
Thanks, that's what I thought it said.

That confirms the results we see in the real world, where there are several billion years of evolution without this "genetic entropy" causing it all to go extinct.

This also supports my idea that you have to believe in a young earth and "the fall" to support the kind of genetic entropy that creationists are pushing.


Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
This message is a reply to:
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slevesque
Member (Idle past 2803 days)
Posts: 1456
Joined: 05-14-2009


Message 22 of 25 (590524)
11-08-2010 3:42 PM
Reply to: Message 18 by Taq
11-08-2010 1:37 PM


Macroevolution does not require the production of new organs. Even "new organs or features" is a misnomer since evolution is descent with MODIFICATION, not evolution of something completely new. For example, the legs of tetrapods are modified fins, not something completely new.

What macroevolution requires is the production of new species. For example, chimps and humans are separate species but no new organs or features had to evolve.

I wrote that opening post very quickly, and I knew this part would be cherry-picked a bit. If you feel you could write a more complete/accurate phrase, please do I could just edit my post and replace it.

But you have to realize that my statement isn't false: evolutionists do think these will accumulate to produce new features, organs, etc. and this would be described as macro-evo. It doesn't contradict that fact that major modification to previously existing structures would also fall into that category as well.

The millions of mutations that separate chimps and humans did not result in non-viable species, so obviously this burden has not occurred yet since chimps and humans shared a common ancestor.

I think we are talking more about observational science right now, observing present-day micro, and deciding if adding all this up could account for the macro that supposedly happened in our distant pass.

Because, supposing it can't, there are still two options:

-there are missing parts of the overall mechanism that we aren't taking into account

-Maybe all this supposed mcro never happened after all (I doubt any of you would consider this option, however)

Creationists need to move beyond "possibility". They need to show that it is an unavoidable consequence. They have failed to do so.

After only two pages of discussion, which include only two posts from a creationist ?

Give me a break please.


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Taq
Member
Posts: 7864
Joined: 03-06-2009
Member Rating: 4.3


Message 23 of 25 (590525)
11-08-2010 3:44 PM
Reply to: Message 21 by Coyote
11-08-2010 2:34 PM


Re: Creationists meltdown?
Another interesting aspect is the differences in the substitution rate between non-coding and coding regions. Just within coding regions we tend to see more synonymous mutations than we do non-synonymous mutations, even though the process of mutation will tend to produce more non-synonymous mutations than synonymous mutations (note: synonymous = mutations which do not change the amino acid sequence). We also tend to see more substitutions in non-coding DNA than in coding regions even though we know that coding regions are just as susceptible to mutation as non-coding regions. So we see an obvious signal of negative selection in the genome.

What I find more interesting is the math. There are 35 million substitution differences between chimps and humans. This is a tiny, tiny portion of all the mutations that have occurred in each lineage. With a conservative mutation rate of 100/individual within a small population of 100,000 that is 10 million mutations in each generation. Obviously, genetic drift does not fix that many mutations, deleterious or otherwise.


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Taq
Member
Posts: 7864
Joined: 03-06-2009
Member Rating: 4.3


Message 24 of 25 (590526)
11-08-2010 4:00 PM
Reply to: Message 22 by slevesque
11-08-2010 3:42 PM


I wrote that opening post very quickly, and I knew this part would be cherry-picked a bit. If you feel you could write a more complete/accurate phrase, please do I could just edit my post and replace it.

There are two major concepts here. First, there is change over time within a single lineage (i.e. temporal change). For example, the theory suggests that the accumulated mutations from australopithecines to H. erectus to modern humans has resulted in macroevolution. In this case we define speciation as morphologically different populations through time. In this case, macroevolution is the accumulation of microevolutionary events over time.

There is also divergence. This is where two lineages split from a common ancestral population. In this case, macroevolution is driven by the accumulation of DIFFERENT microevoutionary events in each lineage. Different mutations and different selective pressures cause the populations to become more divergent over time. Therefore, along with microevolutionary events you also need a mechanism which prevents genetic flow between two populations resulting in divergent lineages.

The interplay of these macroevolutionary mechanisms undergirds the entire debate between phyletic gradualism and punctuated equilibria, in case you were wondering.

I think we are talking more about observational science right now, observing present-day micro, and deciding if adding all this up could account for the macro that supposedly happened in our distant pass.

The observed human mutation rate is well above that needed to produce the genetic differences between chimps and humans over a 5-8 million year period. If accept the rather obvious assumption that the difference in DNA between humans and chimps results in a difference in morphology then we should look at these DNA differences and ask a very simple question. Of these differences which could not have been produced by a mutational event? I know of none. Do you know of any?

-Maybe all this supposed mcro never happened after all (I doubt any of you would consider this option, however)

It is always an option, but there is tons of genetic data that fall in line with evolution. Take the ERV data, for example. When an ERV inserts the flanking LTR's on the viral genome are identical in sequence. This is due to the mechanism of viral replication and insertion. Because there is no selective pressure to keep these two bookend sequences the same once they are part of the genome they will accumulate different mutations causing the LTR's to diverge over time. The longer the ERV has been part of a lineage the more divergent the LTR's will be due to the accumulation of mutations. This is what the theory of evolution predicts we should see. So what do we see? Exactly this pattern. We observe that ERV's found in all apes have higher LTR divergence than ERV's found in just a single ape species or in just two species. For example, an ERV found in orangutans, gorillas, chimps, and humans has a higher LTR divergence than an ERV found in just humans and chimps. The divergence pattern matches the nested hierarchy established by insertion time (as determined by placement in the genome). It is data like this that only evolution can explain, and the type of evidence that ID/creationism seems to avoid like the plague.


After only two pages of discussion, which include only two posts from a creationist ?

Give me a break please.

We are also including the last 60 years of scientifically vacuous creationist arguments, starting with the Henry Morris modern creation science movement. I can also point to the "Describe a creationist experiment" thread. You can't ignore the history.


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Rrhain
Member (Idle past 35 days)
Posts: 6349
From: San Diego, CA, USA
Joined: 05-03-2003


(1)
Message 25 of 25 (590965)
11-10-2010 10:17 PM
Reply to: Message 16 by frako
11-08-2010 5:18 AM


frako responds to Mr Jack:

quote:
quote:
there is good reason to think that the description of macroevolutionary patterns of evolution needs additional mechanisms.

why?
and what additional mechanisms?


While I am not Mr Jack, what I got from his post was that there are certain actions that happen at the level of individuals (and thus individual genes) and then there are actions that happen at the level of populations (and thus pools of genes).

Take, for example, death. If you as an individual die before you are able to reproduce, then the population will lose your individual alleles, and while there are going to be some unique ones that will be lost, the effect on the entire population and thus the species as a whole is likely to be minimal. Or at least more accurate, later evolutionary mechanisms will not be able to function upon your alleles but the diversity of the population is going to be minimally affected by your loss.

But if there is a massive loss of population, then the genetic diversity of the population is going to be dramatically altered and later evolutionary mechanisms will have a very different gene space in which to work. Alleles that might have been in the minority in the larger population may now have a much greater chance of being the base set upon which later evolutionary processes act upon.

If I recall correctly, this is often called the "founder effect" where a small population is isolated from the main group. This can happen via migration, geographical shifts, die offs, etc.

At even larger scales, the extinction of one population can result in evolutionary processes on other populations that might not normally happen. For example, there is some consideration of the idea that it took the death of the dinosaurs to help bring about the reign of the mammals. Even Darwin understood this concept: Different species in the same ecosphere need to find their niche in order to survive. New species that would occupy the same niche as an already established one will find it difficult to gain a foothold. But the removal of a species will allow other species in the system to adapt to fill the vacant niche. The deletion of an adjacant species allows evolutionary processes to start affecting your species in ways that were blocked before due to competition.

So yes, I would agree with Mr Jack that there are effects that happen at larger, "macroevolutionary" scales. Conceivably, they also happen at smaller scales...you, after all, are a population of alleles...but the effects can be so subtle and overwhelmed by other factors that they just don't get a chance to take hold.

All that said, my main point remains: The collection of processes that happen upon generational shifts within a population can accumulate and result in large-scale changes such as speciation.


Rrhain

Thank you for your submission to Science. Your paper was reviewed by a jury of seventh graders so that they could look for balance and to allow them to make up their own minds. We are sorry to say that they found your paper "bogus," specifically describing the section on the laboratory work "boring." We regret that we will be unable to publish your work at this time.

Minds are like parachutes. Just because you've lost yours doesn't mean you can use mine.
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