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Author Topic:   The dilution of the effects of genetic mutation.
RAZD
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Posts: 19759
From: the other end of the sidewalk
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Message 16 of 18 (522564)
09-04-2009 12:28 AM
Reply to: Message 12 by AndrewPD
09-03-2009 6:55 PM


zebras and stripes
Hi AndrewPD, welcome to the fray.

I'm suprised anything has survived this long.

Fortunately, reality is unaffected by your opinion.

And Why would a zebra without the stripes not survive also?

They have.

I get the impression that any feature that survives is attributed to fitness but it seems that any trait that survives is not intending to survive so could have survived simply because it didn't have a negative effect.

Google "neutral mutation" -- you are correct.

Would a striking feature such as the zebra's black and white stripes have occured in one mutation?

Does it need to?

http://en.wikipedia.org/wiki/Equus_(genus)

quote:

Click to enlarge

Quagga (now extinct)

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This message is a reply to:
 Message 12 by AndrewPD, posted 09-03-2009 6:55 PM AndrewPD has not yet responded

  
dwise1
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Joined: 05-02-2006
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Message 17 of 18 (522569)
09-04-2009 3:42 AM
Reply to: Message 1 by AndrewPD
07-23-2009 11:52 AM


Your talk of traits being diluted sounds so incredibly antiquated. Please tell us where you had gotten it from.

You see, when Darwin worked out natural selection, he still was faced with figuring out how a new trait arose and was inherited. Since he did not know about Mendel's work (even though Mendel's monograph was in his bookshelf; has everyone actually read every single book in one's library?), he could not have used it to try to solve the problem before him. From pages 56-57 of Blueprints: Solving the Mystery of Evolution:

quote:
During 1837 and 1838 Darwin wrestled with that dilemma. It brought him face to face with the so-called problem of dilution. Suppose (through some strange agency) an animal came along that was quite different from its fellows. If it were mated to a normal one and its offspring mated to another normal one, and so on, would not its original peculiarity gradually get eliminated in the great pool of normal animals? It would be as if an experimenter poured a half-beaker of dark-pink cranberry juice into a half-beaker of clear water. The result would be a paler pink liquid. Pour half of that into another beaker of water -- paler yet. After a while an observer would be able to detect no pink whatsoever. That, according to the wisdom of the time, was what enabled species to remain stable. An aberration that came along would be swamped by normality.

So why are you recycling an old discredited idea that's so much more than 100 years old? We've know for virtually all of the 20th century and beyond about genetics, that these genes are discrete and thus incapable of being diluted. That these genes can still be carried in individuals without actually being expressed in the carrier's phenotype.

Here's basically what happened. Darwin had worked out how natural selection would select for new traits, but he had no way to work out how those new traits could arise nor how they could establish themselves in a population. The conceptual model he used was pigments getting mixed into paint, in which case the new trait would be "diluted" out of existence, just as you had postulated.

So, what Darwin ended up doing was to come up with his "pangenetic" theory, which was basically neo-Lamarckian. It was quite obviously wrong. So as the scientific community became increasingly aware of Mendelian genetics, it also became increasingly aware of how wrong Darwin's pangenetic theory was. Creationists love to quote early 20th-century geneticists as disproving Darwin, but they neglect to tell you that those geneticists were only disproving Darwin's pangenetic theory and not natural selection.

It was the later study of population genetics that demonstrated that genetics answered Darwin's unanswered questions about heredity, which brought about the modern evolutionary synthesis and neo-Darwinism. It is through population genetics that your "dilution problem" is answered. We've known that answer since about 1940. Isn't it time you learned it too?


This message is a reply to:
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Dr Adequate
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Joined: 07-20-2006
Member Rating: 10.0


Message 18 of 18 (522745)
09-04-2009 5:07 PM
Reply to: Message 14 by AndrewPD
09-03-2009 9:11 PM


If the stripes were effective when there was a mass of Zebras together then just one Zebra becoming striped would have stood out like a sore thumb.

No, not necessarily. Even assuming, as you do, that there was a sudden leap from non-striped to striped, it is arguable that if you have a bunch of equids, only one of which is striped, dashing about in front of a bunch of lions which are also dashing about, then the striped zebra would be more visually confusing ... especially to lions who have not evolved to hunt striped zebras, and whose instincts are attuned to hunting zebras that are pure blocks of color.


This message is a reply to:
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