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Author Topic:   Peppered Moths and Natural Selection
Percy
Member
Posts: 17645
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.9


Message 317 of 350 (670713)
08-17-2012 1:46 PM
Reply to: Message 311 by Big_Al35
08-17-2012 11:02 AM


Big_Al35 writes:

Populations and species are protected from the harsh dangers of natural selection.

I think what you're really trying to say is that detrimental alleles that are recessive can much more easily escape selective pressures than detrimental alleles that are dominant. I don't think anyone would argue with this.

Where we might believe that certain traits have been wiped of the face of the earth through "survival of the fittest", those attributes can live on, hidden and preserved, within the genome.

While not impossible, it is extremely unlikely for recessives to never be expressed in a population, though it is possible for a rare recessive allele to disappear. Say only one member of the population possesses this rare recessive allele and he dies before producing any offspring. The recessive allele is now extinct, which is the only way natural selection can remove an allele.

But say this individual reproduces. Half his offspring, on average, will carry the recessive allele, and a quarter of their offspring, and an eighth of their offspring, so on through all the generations that follow. Recessive genes propagate easily through a population, and soon many members will possess it, even though it began with just a single individual. If any two descendants of this individual who happen to possess the recessive allele should ever mate, 25% of their offspring will have two copies of the recessive gene and it will be expressed.

So you can see that even if a recessive allele is present in only a single individual, unless he dies without reproducing the odds say that the recessive gene will be expressed in descendants. The recessive gene cannot hide so completely that we're unaware that it exists. (Although of course the exception would be alleles that express themselves in such subtle ways that their effect goes undetected, but that's a separate issue.)

I am glad that we can "kind of" agree on this more modern definition of natural selection.

Me too. It's been plastered all over the Internet for years, including at this website.

--Percy


This message is a reply to:
 Message 311 by Big_Al35, posted 08-17-2012 11:02 AM Big_Al35 has responded

Replies to this message:
 Message 319 by Big_Al35, posted 08-17-2012 2:20 PM Percy has responded

    
Granny Magda
Member (Idle past 80 days)
Posts: 2372
From: UK
Joined: 11-12-2007


(2)
Message 318 of 350 (670715)
08-17-2012 2:03 PM
Reply to: Message 314 by Big_Al35
08-17-2012 1:14 PM


Let's use your definition ie "survival of the just good enough". If the environment was so harsh that a particular trait could not even survive long enough to reproduce, then only individuals who are actively expressing that trait would disappear.

Sure. But it would still continue to be expressed. It's just that those individuals would be less successful. That is hardly "hidden", just less widespread.

It is possibly worth noting that there can be other reasons why a gene might not be expressed. Birds, for example, still carry the genes necessary to create teeth, but these genes are not expressed in the phenotype. It's nothing to do with dominance/recessiveness, but to do with developmental factors.

The unexpressed allele would still linger on in the population at large. These harsh conditions could even continue for thousands or millions of years. In every generation where the allele is expressed, the individual would die.

Well, not every individual, not necessarily. But yes, those individuals that expressed the poorly adapted allele would become markedly less common, or die out. That is natural selection. That's what natural selection is. Everything you've said here supports the standard evolutionary understanding of natural selection.

However, after enough time had passed, circumstances or the environment might change. Individuals who are now expressing the gene may actually survive or even flourish. The example that I am thinking of is the peppered moths.

Yes. It's a rather beautiful piece of evidence in favour of natural selection. Every single thing you've said here supports natural selection. Not that I have a problem with that; I just want you to understand that none of this is an objection to natural selection, indeed, it's quite the reverse.

Mutate and Survive

Edited by Granny Magda, : No reason given.


This message is a reply to:
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Big_Al35
Member (Idle past 284 days)
Posts: 384
Joined: 06-02-2010


Message 319 of 350 (670717)
08-17-2012 2:20 PM
Reply to: Message 317 by Percy
08-17-2012 1:46 PM


Percy writes:

I think what you're really trying to say is that detrimental alleles that are recessive can much more easily escape selective pressures than detrimental alleles that are dominant. I don't think anyone would argue with this.

Not exactly, some alleles can be both dominant and recessive. Let's say we had alleles A, B and C. A might be dominant to B but recessive to C. B is recessive to A but dominant to C. And C is dominant to A but recessive to B. This might allow A, B and C to be bulletproof from being selected out of the gene pool.


This message is a reply to:
 Message 317 by Percy, posted 08-17-2012 1:46 PM Percy has responded

Replies to this message:
 Message 320 by Percy, posted 08-17-2012 6:03 PM Big_Al35 has responded

    
Percy
Member
Posts: 17645
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.9


(1)
Message 320 of 350 (670728)
08-17-2012 6:03 PM
Reply to: Message 319 by Big_Al35
08-17-2012 2:20 PM


Hi Big Al,

So what about your main point? Everyone who responded is still completely puzzled as to why you're using a prime example of natural selection at work to argue that some alleles are protected against natural selection.

You are correct that some parts of the genetic code *are* protected against natural selection (but not against mutation), but recessive alleles are not an example of this. A better example would be disabled genes that cannot be selected for or against because are not expressed, but the disabled gene is understood to be yet another mechanism of evolution, through further mutation and eventual re-enabling.

--Percy


This message is a reply to:
 Message 319 by Big_Al35, posted 08-17-2012 2:20 PM Big_Al35 has responded

Replies to this message:
 Message 321 by RAZD, posted 08-17-2012 7:36 PM Percy has acknowledged this reply
 Message 327 by Big_Al35, posted 08-19-2012 10:22 AM Percy has responded
 Message 333 by Big_Al35, posted 08-20-2012 4:21 AM Percy has responded

    
RAZD
Member
Posts: 19544
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.3


Message 321 of 350 (670730)
08-17-2012 7:36 PM
Reply to: Message 320 by Percy
08-17-2012 6:03 PM


so is it summary time?

if anyone wants, I'll be happy to start a thread on sickle-cell and natural selection.

or perhaps one on "protection" of unexpressed genes from natural selection

Enjoy

Edited by RAZD, : .


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
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This message is a reply to:
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pandion
Member (Idle past 893 days)
Posts: 166
From: Houston
Joined: 04-06-2009


(2)
Message 322 of 350 (670741)
08-18-2012 1:48 AM
Reply to: Message 308 by Big_Al35
08-17-2012 3:52 AM


I have supplied you with two definitions for natural selection.

Neither of which is adequate, one being fundamentally erroneous.
An old darwinian definition "survival of the fittest"

But that isn't Darwinian by any means. Darwin only used that term in the 5th edition (of six) of "On The Origin Of Species," published some 9 years and 3 months after the original publication of the book (Nov. 1859 to Feb. 1869). Darwin never liked the term and never used it without making a reference to his theory, natural selection. The phrase, "survival of the fittest," was coined by the socialist philosopher, Herbert Spencer, after he had read Darwin's book. Darwin finally used the phrase after it had become common as a reference to his theory. He only did so after convincing by T.H. Huxley.

So you are wrong. "Survival of the fittest" isn't an old Darwinian definition but an incorrect understanding of Darwin's theory that was forced on him by a social theorist whose idea was accepted by the populous.

and another which I have conjured up myself.

I have to wonder why you thought that was necessary. Why do you not think that the biological definition of natural selection, used by evolutionary biologists everywhere and the one that I learned more that 40 years ago is sufficient?
I am totally bemused as to how you have chosen to define natural selection, as "screening process" doesn't really tell me anything.

Nor does your definition tell anyone anything. Let's see. What did you say?
quote:
Natural selection, rather than being defined as "survival of the fittest" might be better viewed as "allele domination under significant environmental and sexual selection pressures".

Well, at least you seem to recognize that "survival of the fittest" is a totally erroneous definition of natural selection. However, your definition is unnecessary and extraneous. Why not go with the definition used by evolutionary biologists? Looking at natural selection as a screening process is a pretty good understanding of the concept.
Perhaps you would be kind enough to offer your own definition.

I would be happy to. This is the definition that I learned more than 40 years ago and that is still used by evolutionary biologists today.

Natural selection is the differential reproductive success of organisms that possess benificial genetic traits (that lend a reproductive advantage).

I added the parenthetical phrase in order to clarify for you. That parenthetical phrase is actually redundant.

And as for mutation, I didn't even mention mutation once in my post. Does mutation have anything to do with this topic?

As noted, mutation is one of the sources of genetic diversity upon which natural selection acts. Mutation and natural selection are but 2 of the 9 recognized mechanisms of evolution. Would you like to learn about them?
This message is a reply to:
 Message 308 by Big_Al35, posted 08-17-2012 3:52 AM Big_Al35 has responded

Replies to this message:
 Message 323 by RAZD, posted 08-18-2012 5:58 AM pandion has not yet responded
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RAZD
Member
Posts: 19544
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.3


Message 323 of 350 (670742)
08-18-2012 5:58 AM
Reply to: Message 322 by pandion
08-18-2012 1:48 AM


new topic? current topic drift? current topic summary mode?
Hi pandion,

I note two things:

(1) the topic is starting to drift away from peppered moths as an example of natural selection into a general discussion of natural selection, and

(2) the topic is at the point where admins usually instigate summary mode posting.

I would like to see this discussion continue, but feel that this really should be a new topic, especially as it might go long and might need many baby steps to explain individual points.

As noted, mutation is one of the sources of genetic diversity upon which natural selection acts. Mutation and natural selection are but 2 of the 9 recognized mechanisms of evolution. Would you like to learn about them?

9 recognized mechanisms of evolution would be a great new topic.

Enjoy

abe: or if you want, you could join me (or im me to discuss) on Introduction to Evolution

Edited by RAZD, : ps


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
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NoNukes
Inactive Member


(1)
Message 324 of 350 (670748)
08-18-2012 9:58 AM
Reply to: Message 308 by Big_Al35
08-17-2012 3:52 AM


Plonk
Discussion with you isn't worth the effort.

I don't need a definition of natural selection. I know what natural selection is. What I don't understand is what sequence of events you are attempting to call natural selection or your references to Mendel's work.

I asked questions because I hoped you'd make your position more clear. Instead you elected to deal out insults to a complete stranger.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

The apathy of the people is enough to make every statue leap from its pedestal and hasten the resurrection of the dead. William Lloyd Garrison.

Choose silence of all virtues, for by it you hear other men's imperfections, and conceal your own. George Bernard Shaw


This message is a reply to:
 Message 308 by Big_Al35, posted 08-17-2012 3:52 AM Big_Al35 has responded

Replies to this message:
 Message 326 by Big_Al35, posted 08-19-2012 10:05 AM NoNukes has not yet responded

  
Big_Al35
Member (Idle past 284 days)
Posts: 384
Joined: 06-02-2010


Message 325 of 350 (670802)
08-19-2012 10:02 AM
Reply to: Message 322 by pandion
08-18-2012 1:48 AM


pandion writes:

Natural selection is the differential reproductive success of organisms that possess benificial genetic traits (that lend a reproductive advantage).

Classic evolutionary tautology. The reproductive success of organisms that have traits which promote reproductive success. The reason this is nonsense is because it contains no information. Reproductive success (not quantified) used twice and traits (quantified only by reproductive success which remains undefined).

Sorry but your definition is garbage.


This message is a reply to:
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Replies to this message:
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 Message 329 by pandion, posted 08-19-2012 12:57 PM Big_Al35 has not yet responded
 Message 332 by crashfrog, posted 08-19-2012 2:58 PM Big_Al35 has not yet responded

    
Big_Al35
Member (Idle past 284 days)
Posts: 384
Joined: 06-02-2010


Message 326 of 350 (670803)
08-19-2012 10:05 AM
Reply to: Message 324 by NoNukes
08-18-2012 9:58 AM


Re: Plonk
NoNukes writes:

I asked questions because I hoped you'd make your position more clear. Instead you elected to deal out insults to a complete stranger.

Ok...I might have been a little harsh with you but no harsher than others have been with me. I suggest you grow a pair.


This message is a reply to:
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Big_Al35
Member (Idle past 284 days)
Posts: 384
Joined: 06-02-2010


Message 327 of 350 (670804)
08-19-2012 10:22 AM
Reply to: Message 320 by Percy
08-17-2012 6:03 PM


Percy writes:

So what about your main point? Everyone who responded is still completely puzzled as to why you're using a prime example of natural selection at work to argue that some alleles are protected against natural selection.

I think everyone accepts that natural selection occurs but it's the nature of natural selection and the sequence of events that we are discussing here. I have used the example of the peppered moths. Two or more types of moth (namely dark and light existed prior to the event ie industrialization) and two or more types existed after the event. It was simply a case of which type of moth flourished when.
Therefore I wouldn't view this is as an example of evolution. Others might disagree.

You and some others here have introduced mutation into the equation. This may account for genuine micro-evolution but has nothing to do with the example I was discussing.


This message is a reply to:
 Message 320 by Percy, posted 08-17-2012 6:03 PM Percy has responded

Replies to this message:
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Dr Adequate
Member
Posts: 16035
Joined: 07-20-2006
Member Rating: 3.8


(2)
Message 328 of 350 (670806)
08-19-2012 10:55 AM
Reply to: Message 325 by Big_Al35
08-19-2012 10:02 AM


Classic evolutionary tautology. The reproductive success of organisms that have traits which promote reproductive success. The reason this is nonsense is because it contains no information. Reproductive success (not quantified) used twice and traits (quantified only by reproductive success which remains undefined).

Classic creationist blunder. The reproductive advantage of traits can be assessed a priori, not merely a posteriori: for example, it is evident that the better-camouflaged moth has a trait which promotes reproductive success, namely better camouflage, which we would expect to keep it from being eaten by predators.

The statement that such traits will in fact spread through the gene pool is not at all tautologous, since we can imagine circumstances (such as the miraculous intervention of a vengeful god with a grudge against mutants) under which this would not occur, despite our a priori judgement that the trait is favorable.

Edited by Dr Adequate, : No reason given.


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pandion
Member (Idle past 893 days)
Posts: 166
From: Houston
Joined: 04-06-2009


(1)
Message 329 of 350 (670808)
08-19-2012 12:57 PM
Reply to: Message 325 by Big_Al35
08-19-2012 10:02 AM


Well, I added the parenthetical phrase at the end because I knew that you didn't understand the concept. Anyone who furnishes "survival of the fittest" as a substitute for Darwin's theory of natural selection doesn't understand the subject. The definition, "survival of the fittest," is most definitely a tautology. Differential reproductive success of individuals with beneficial genetic traits isn't - unless, of course, you intentionally misrepresent what it says.
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Dr Adequate
Member
Posts: 16035
Joined: 07-20-2006
Member Rating: 3.8


Message 330 of 350 (670809)
08-19-2012 1:35 PM
Reply to: Message 329 by pandion
08-19-2012 12:57 PM


The definition, "survival of the fittest," is most definitely a tautology.

Not necessarily, and for the same reason --- we can assess fitness a priori. Other things being equal, the well-camouflaged moth is fitter than the poorly-camouflaged moth, the more streamlined fish is fitter than the less streamlined fish, the faster gazelle is fitter than the slower, the bacterium resistant to our antibiotics is fitter than the one that isn't.

And again we can imagine a world in which a malevolent deity (or some other hypothetical mechanism) thwarts our a priori expectations of their relative likelihood of success and failure.


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RAZD
Member
Posts: 19544
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.3


(2)
Message 331 of 350 (670810)
08-19-2012 2:19 PM
Reply to: Message 327 by Big_Al35
08-19-2012 10:22 AM


once more around the bend ...
Hi Big_Al35

... Two or more types of moth (namely dark and light existed prior to the event ie industrialization) and two or more types existed after the event. It was simply a case of which type of moth flourished when.
Therefore I wouldn't view this is as an example of evolution. Others might disagree.

You and some others here have introduced mutation into the equation. This may account for genuine micro-evolution but has nothing to do with the example I was discussing.

Let me see if this helps:

The diagram is simplified, as breeding variations can exist through several generations (being due to existing mutations plus new mutations), as is the case with the peppered moths such that some with less the favorable camouflage still survive to breed in either ecological condition.

Therefore I wouldn't view this is as an example of evolution. Others might disagree.

Correct:

Evolution involves a full cycle of the loop, so no, natural selection alone is not and example of evolution per se. This is a common creationist mistake: when you walk you don't only use one leg, but alternate from one to the other, and the cycle of evolution is a similar process.

Micro-evolution is evolution within breeding populations. Macro-evolution is the continued evolution of populations looked over many generation cycles and many breeding populations of the same species. There is no difference in the mechanisms involved other than time scale and the focus of the observation (the occurrence of variations versus the accumulation of variations).

If you want to discuss micro vs macro, I suggest another thread as that will definitely be off topic on this thread that is about part of (micro) evolution. see MACROevolution vs MICROevolution - what is it? for example (note you will need to define what YOU think they are in order to form a basis for discussion). You may also want to read Introduction to Evolution (still a proposed topic so not open for comments).

... Two or more types of moth (namely dark and light existed prior to the event ie industrialization) and two or more types existed after the event. It was simply a case of which type of moth flourished when.

Exactly:

  • prior to the industrialization the population consisted of two variations within a species, with breeding and gene flow between the varieties (because varieties are a division below species due to interbreeding), with a higher proportion of light (say 80%) than dark (20%)
  • during the industrialization event the proportion shifted to higher proportion of dark (say 80%) than light (20%) due to the change in advantage of dark camouflage on dark ecologies from and advantage of light camouflage on light ecologies -- and
  • when the industrialization event ended and the ecology switched back so did the proportions of light and dark moths.

This is because the ecologies in either case did not prevent the less advantaged camouflage group to survive at a low level so they were not all killed and eaten.

Natural selection does not necessarily involve wiping out one variety in favor of another, but in changing the proportion of the different varieties that survive to breed (lower right box). The frequencies of the different hereditary traits change.

Enjoy


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

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