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Author Topic:   The End of Evolution By Means of Natural Selection
Rakshas
Junior Member (Idle past 2903 days)
Posts: 4
Joined: 02-05-2011


Message 842 of 851 (606365)
02-25-2011 6:18 AM
Reply to: Message 838 by Dr Adequate
02-24-2011 12:46 PM


Re: Where is the end, if there is no beginning?
Yes, I am forced to use the Google translator
This message is a reply to:
 Message 838 by Dr Adequate, posted 02-24-2011 12:46 PM Dr Adequate has responded

Replies to this message:
 Message 843 by Dr Adequate, posted 02-25-2011 6:55 AM Rakshas has not yet responded

    
Dr Adequate
Member
Posts: 16096
Joined: 07-20-2006


Message 843 of 851 (606369)
02-25-2011 6:55 AM
Reply to: Message 842 by Rakshas
02-25-2011 6:18 AM


Re: Where is the end, if there is no beginning?
Yes, I am forced to use the Google translator

An Indian, I assume from your username.

You may do better to try to put your thoughts into English yourself. Automatic translators aren't all that good. It's OK searching for particular words, but if you have any English at all you'll probably do the grammar better than any machine will.


This message is a reply to:
 Message 842 by Rakshas, posted 02-25-2011 6:18 AM Rakshas has not yet responded

  
Scienctifictruths
Member (Idle past 1003 days)
Posts: 32
Joined: 05-30-2011


Message 844 of 851 (618985)
06-07-2011 12:00 PM
Reply to: Message 834 by Rakshas
02-06-2011 2:19 AM


Re: Where is the end, if there is no beginning?
Deleted.

Edited by Scienctifictruths, : Still getting used to the month/day/year setup; confusion.


This message is a reply to:
 Message 834 by Rakshas, posted 02-06-2011 2:19 AM Rakshas has not yet responded

Replies to this message:
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 Message 846 by Percy, posted 06-07-2011 7:17 PM Scienctifictruths has not yet responded

    
New Cat's Eye
Inactive Member


Message 845 of 851 (618988)
06-07-2011 12:17 PM
Reply to: Message 844 by Scienctifictruths
06-07-2011 12:00 PM


Still getting used to the month/day/year setup; confusion.


This message is a reply to:
 Message 844 by Scienctifictruths, posted 06-07-2011 12:00 PM Scienctifictruths has not yet responded

  
Percy
Member
Posts: 18484
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.8


Message 846 of 851 (619046)
06-07-2011 7:17 PM
Reply to: Message 844 by Scienctifictruths
06-07-2011 12:00 PM


Re: Where is the end, if there is no beginning?
Not sure where the month/day/year confusion you mention stems from, but if it's the way dates are rendered here at EvC Forum then you can change them to the European style. Just go to your profile (link is near the top left of the page) and scroll down to the Date Format line. A bunch of European formats are available, just pick your favorite, then click on Submit Changes.

--Percy

Edited by Percy, : Spelling.


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richdix
Junior Member (Idle past 2837 days)
Posts: 4
Joined: 06-09-2011


Message 847 of 851 (619222)
06-09-2011 8:23 AM


The additive measure of allele elimination
In the real world, alleles are usually only in competition with one other allele. For instance, an allele for fur colour that provides better camouflage than the existing predominant fur colour of the species is only in competition with the existing predominant allele. Thus most often, one allele replaces another. This also works in reverse for deleterious alleles. Add to this consideration of the fact that the vast majority of allele variations confer neither a beneficial or a deleterious effect on their recipients, and what you have is an extremely variable species. Natural selection does not eliminate variation.

Next consider the environment - it is not static. Also, many species are migratory. The survival value of an allele is not an absolute - it is relative to the changing environment(s). Furthermore, the genetic environment is not static - all species around our hypothetical focus species are also evolving, changing the survival value of alleles in our focus species. Natural selection does not eliminate variation.


Replies to this message:
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Wounded King
Member (Idle past 2259 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 848 of 851 (619225)
06-09-2011 8:59 AM
Reply to: Message 847 by richdix
06-09-2011 8:23 AM


Re: The additive measure of allele elimination
In the real world, alleles are usually only in competition with one other allele.

I'd say this was a pretty contentious claim. It might be true looking at a traditional readily identifiable Mendelian characteristic, such as your coat colour example, but for any complex trait it is almost certainly false.

Comparative genomics within populations has revealed a large amount of heterogeneity at both the copy number and SNP level and whole genome association studies have identified small but still significant effects from such variations. So there could easily be multiple SNP variants of a gene or set of genes interacting with the environment to produce a spectrum of fitness.

TTFN,

WK


This message is a reply to:
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Replies to this message:
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richdix
Junior Member (Idle past 2837 days)
Posts: 4
Joined: 06-09-2011


Message 849 of 851 (619319)
06-09-2011 1:10 PM
Reply to: Message 848 by Wounded King
06-09-2011 8:59 AM


Re: The additive measure of allele elimination
What you say is technically correct, but I was specifically talking about alleles and not traits, which as you say can have more complex ontogenies. However, if we shift the focus to traits the same basic principle holds. It will almost always be a case of the emergent trait versus the predominant trait when one is more beneficial than the other.

Traits that have several predominant varieties (such as eye colour) are almost always neutral in terms of natural selection (note that I am not introducing sexual selection into this topic). When a trait is subject to natural selection it's variability is necessarily highly restricted. You can't have massive leaps in genetic space and expect to land in a favourable position, the odds are far too high.

Traits that are the product of complex gene interractions are often found in behaviour. Imagine the number of possible (however apparently absurd) behaviours there are for a situation such as being confronted by a predator. Compare that with the number of behaviours that would be as or more beneficial than the predominant trait. This rough calculation gives you an idea of the extent to which such complex traits are constrained.

Whether talking about alleles or complex traits the situation remains one versus one in most cases, as long as you only compare like with like (ie traits with traits, alleles with alleles). I will search for exceptions to this to falsify my point. If I find I'm utterly wrong I will reply and tell you.


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richdix
Junior Member (Idle past 2837 days)
Posts: 4
Joined: 06-09-2011


Message 850 of 851 (619342)
06-09-2011 2:28 PM
Reply to: Message 848 by Wounded King
06-09-2011 8:59 AM


Re: The additive measure of allele elimination
In all concrete observed instances of speciation by natural selection that I can find (though there aren't that many), the speciation event has centred around a single trait or class of traits (eg bird song). I cannot find an example of a single allele being naturally selected directly resulting in a speciation event. That's not to say it doesn't happen, but direct observation of this phenomenon is clearly problematic.

In examples such as ring species, natural selection is often inferred to be the cause of the initial reproductive isolation of two previously interbreeding populations, but not directly observed.

There are of course many examples where natural selection acts on a single gene (eg the sickel cell anaemia gene that protects against malaria), but speciation has not yet been properly observed in such cases.

So, from what I can find it seems as though natural selection does usually select one trait or allele in favour of one competing trait or allele (or lack thereof).

If you can find an example that bucks that trend i would be very happy to hear it. Unlike many people in these forums I have no problem with being proven wrong - as that is exactly how science advances (not that I have over inflated ideas about the importance of these forums of course).

Best regards,

richdix.


This message is a reply to:
 Message 848 by Wounded King, posted 06-09-2011 8:59 AM Wounded King has responded

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Wounded King
Member (Idle past 2259 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 851 of 851 (619557)
06-10-2011 11:46 AM
Reply to: Message 850 by richdix
06-09-2011 2:28 PM


I'm not really sure what you are saying
In all concrete observed instances of speciation by natural selection that I can find (though there aren't that many), the speciation event has centred around a single trait or class of traits (eg bird song).

You seem to assume that natural selection is the normal driver for speciation, there is considerable reason to doubt this even from the same sort of bird song ring species studies you refer to. Indeed one of the main points arising from the study of the greenish warbler ring species is that the variations in song seem to be stochastic, resulting primarily from either cultural or genetic drift, rather than a product of selection (Irwin et al, 2008).

There are of course many examples where natural selection acts on a single gene (eg the sickel cell anaemia gene that protects against malaria), but speciation has not yet been properly observed in such cases.

A single gene can have many alleles, even the sickle cell anaemia allele HbS is only one of 2 known haemoglobin alleles which offer some protection from malaria (Verra et al, 2007).

So, from what I can find it seems as though natural selection does usually select one trait or allele in favour of one competing trait or allele (or lack thereof).

I can't see how this relates to what you say about speciation and ring species. I also don't see any evidence for this claim and, as I pointed out previously, there is a staggering weight of genetic evidence countering it. Perhaps you are using some idiosyncratic definition of what constitutes an allele, or discounting all neutral or nearly neutral allelic variants?

And now you are conflating traits and alleles, which makes things even more confusing. To be clear, do you claim that most genes only have at most 2 alleles?

If you can find an example that bucks that trend i would be very happy to hear it.

So one example would be the Malaria resistant Haemoglobin variants (A,C and S)which currently forms a dynamic balance in the population. Heterozygotes of both AC and AS can be selected for in response to malarial pressures while for heterozygotes CC is very mild in terms of symptoms compared to SS. This also emphasises another another exception to your claim that natural selection will tend to favour one of two alleles, heterozygote advantage where heterozygotes have higher fitness than homozygotes of either allele.

TTFN,

WK


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