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Author Topic:   How can evolution explain body symmetry?
jar
Member (Idle past 394 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004


Message 61 of 284 (112185)
06-01-2004 7:08 PM
Reply to: Message 57 by CrackerJack
06-01-2004 5:04 PM


Re: If you want to make a case for the rightness
CrackerJack writes:
I am making a case out of the general observed bilateral external symmetry of animals.
Okay, let's look at that and see if there is anything reasonable there.
First, since ALL life Evolved from something earlier, we can not seperate plants from animals. But to humor you as you begin your search for understanding, let's begin by looking at animals.
The first step is to see if you agree that the basic symmetry was a result of life first appearing in a water environment.
Do you agree with that as a starting point?

Aslan is not a Tame Lion

This message is a reply to:
 Message 57 by CrackerJack, posted 06-01-2004 5:04 PM CrackerJack has not replied

  
nator
Member (Idle past 2170 days)
Posts: 12961
From: Ann Arbor
Joined: 12-09-2001


Message 62 of 284 (112243)
06-01-2004 9:20 PM
Reply to: Message 37 by CrackerJack
06-01-2004 6:32 AM


Re: Once more slowly
quote:
To define precisely how often it would occur, I would have to collect data on what is the ratio between symmetrical and asymmetrical mutations, then we have to decide on what the mutation rate is when evolution is occurring and do some calculations. Being that current biologists are tending towards rapid mutations in a short time, followed by long periods of stability, I assume the mutation rates they are expecting during the evolutionary steps are quite high. The higher the mutation rate, the more frequent you will see multiple mutations piggybacking on the main mutation(s) responsible for the step. Being we don't observe this type of mutation happening (at least not quick enough to measure), we have no way of knowing what exactly is the mutation rate at the point of these evolutionary steps. Thus no way of calculating it precisely.
You seem to be talking about Puntuated Equilibrium, but doing so inaccurately.
PE has nothing to do with mutation rates.
Mutation rates are more or less constant, barring exposure to chemical mutagens, etc.
You are also under the mistaken impression that any, or every, given mutation is likely to spread throughout the population as a whole.
Only those mutations that confer a strong adaptive benefit are likely to spred through a population.
quote:
From an evolutionary perspective and from your perspective they may be fundamentally the same, but they are certainly not the same from mine.
Since we are discussing science, your personal perspective is irrelevant.
quote:
But it really doesn't matter as you say. I was referring to animal symmetry, and not to plants or microscopic organisms and I was not the one who brought up plants.
But you are the one that is making a genetic, evolutionary distinction between plants and animals where there isn't one.
Plant and animal DNA and RNA are made of exactly the same molecules (A,G,T,C), and mutations and meiosis and mitosis happens the same way.
The reason we see more asymmetry in plants compared to animals is because they do not locomote and they don't sexually select.
Why do you refuse to consider plant evolution other than because it weakens your argument, just like your refusal to consider internal asymmetry in animals weakens your argument.
What you are doing is ignoring 99% of Earth's life forms by considering only the external appearance of land animals.
Most life is in the ocean, most land life is not animal.
Furthermore, you are even ignoring more than 50% of the bodies of those land animals because you refuse to consider internal asymmetry.
quote:
Then why do you and everyone else keep harping on selection for symmetry based on sexual attraction and locomotion?
Because for the VERY narrow slice of life you're talking about; the skeletal plan and external surface of land vertebrates; these are known to be important selection pressures. These do NOT hold universally. Locomotion is not an important pressure for non-motile organisms (sponges and corals, plants, fungi), and not all life exhibits sexual selection for symmetry. Both of these are important for all or nearly all land vertebrates, however.
quote:
On the one hand you are saying that evolution is selecting for symmetry for these reasons, and on the other hand saying it is selecting for the environment.
Sexual selection and locomotion are the environment.
I think maybe you might want to read a basic explanation of Evolutionary Biology, such as the one found here:
http://www.talkorigins.org/faqs/faq-intro-to-biology.html
quote:
Well you are trying to take both sides of the fence and it doesn't work that way. Pick one side or the other and stick to it.
That's rich!
You have basically claimed that every example of symmetry AND every example of asymmetry proves your point.
quote:
Your showing of these asymmetrical features proves that sexual attraction does not always work.
I never said it did in every single case.
Visual symmetry is not important in ALL animals for sexual selection, just like not all femalse are attracted to vivid external coloring in the males.
Symmetry is important in humans, however.
quote:
If it didn't work in these cases, you specified, then we first should assume it never works unless it can be proven otherwise.
It has been shown in many animals.
Why do you require that it be all?
quote:
It is certainly proven in humans that it can be a factor, but I have seen no evidence that it is effective in any of the lower life forms.
Sexual selection is one of at least three reasons why symmetry may be maintained.
We know it's true in some cases, and we don't know if it is true in other cases. It is a hypothesis that can be tested, however, unlike the Intelligent Desihner idea, which cannot be tested at all.

This message is a reply to:
 Message 37 by CrackerJack, posted 06-01-2004 6:32 AM CrackerJack has not replied

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 63 of 284 (112343)
06-02-2004 7:03 AM
Reply to: Message 44 by CrackerJack
06-01-2004 6:51 AM


crackerjack writes:
Then why is the external body not symmetrical, and why are there minor, not easily seen, asymmetries of the external body which you already agree exist?
There are a couple of reasons for this. One is that development is a stochastic process and there is always a possibility that some initial gradient or other probabilistic factor will not be set up or operate quite as it should ideally. The other closely related reason is that development is highly sensitive to environmental factors, fluctuating asymmetry which was reffered to in one of Crashfrog's references is a random deviation from normal symmetry and is a result of the interplay of environmental factors and natural random variations in development with the regulatory mechanisms of the developmental system. FA can be used as a measure of the precision of a developmental mechanism. FA can be affected by stress, interbreeding, hybridisation and heterozygosity.
This paper discusses the difficulty in determining devlelopmental stability through studying FA due to many confounding factors, it offers some hope however that improved knowledge of developmental systems and improved statistical tools will make the job easier.
The other question of how symmetry breaking comes about in the internal organs is a much more interesting and complicated one.
TTFN,
WK

This message is a reply to:
 Message 44 by CrackerJack, posted 06-01-2004 6:51 AM CrackerJack has not replied

  
arachnophilia
Member (Idle past 1344 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 64 of 284 (112354)
06-02-2004 8:13 AM
Reply to: Message 6 by CrackerJack
05-30-2004 11:26 PM


dunno if this has been pointed out before.
know someone who has one extra digit on their right hand, but only the normal five on their left. The same with his mother, grandfather, etc. back through his family history. So his body is not symmetrical.
so from your earlier argument, your friend could not have been intelligently designed.
These sorts of mutations that cause asymmetry are quite common, so why haven't many such asymmetries propagated throughout the history of evolution?
answer: THEY ARE.
take a picture of yourself looking STRAIGHT into a camera. cut the photo in half in some photoshop-like program, and make two pictures. one of only right sides, and one of only left. compare.
human beings are not symmetrical.
if you want to go farther, take an anatomy class. we have three lobes on one lung, two on the other. our heart is offset to one side. in fact, MOST of our internal organs are assymetric, including the brain.
studies have also shown that people rate perfectly symmetrical images of people (photoshopped as above) as more attractive than asymmetric ones. therefor, symmetry is a property selected for, via natural selection.

This message is a reply to:
 Message 6 by CrackerJack, posted 05-30-2004 11:26 PM CrackerJack has not replied

  
crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 65 of 284 (112418)
06-02-2004 1:52 PM
Reply to: Message 52 by CrackerJack
06-01-2004 8:35 AM


But I don't agree it is due to sexual selection because I've still not seen the proof of it.
I've shown you several studies where individuals - of a number of species - prefer more symmetric mates. What else do you need, exactly?
You're going to need to find an example where animals can detect general asymmetric mutations at any random point, and not one at some specific point that it being used for sexual selection.
Why? If they can see the symmetry in a sex comb, you don't think they can see it anywhere else?
Saying "seem able" seems to say they are not sure that it is absolutely true.
So, you'd prefer the explanation involving the designer we can never see, never find, and never ever know anything about, just because I can't honestly tell you that I know the scientific explanation is "absolutely true"? If you think scientific tentativity is the place you're going to be able to squeeze in God, I'm not even sure you're capable of understanding scientific conclusions.
So everytime it doesn't use the shortcut there should be a chance for asymmetries.
And there is. The fiddler crab, and others. Again, showing you that symmetry isn't universal has been the subject of some ten posts to you so far.
Christ it's like you forget our posts the second you're finished reading them. You do know that you're supposed to remember our arguments, right?

This message is a reply to:
 Message 52 by CrackerJack, posted 06-01-2004 8:35 AM CrackerJack has not replied

  
jar
Member (Idle past 394 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004


Message 66 of 284 (112419)
06-02-2004 2:03 PM


Crackerjack
there is a question on the table.
Can you respond to Message 61 please?

Aslan is not a Tame Lion

  
crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 67 of 284 (112423)
06-02-2004 2:40 PM
Reply to: Message 54 by CrackerJack
06-01-2004 9:36 AM


But that is still much better than any human built machine
There's a clock in Winnsboro SC that's been running continuously for 160 years. I'm not sure how much replacing of parts you could do on a running clock, so I imagine that the movement, at least, is all original parts.
And the fact that the death rate is so high or that diseases and old age play a part says nothing about the designer's abilities or intentions.
I disagree. It's a well-understood principle of engineering that engineers must take into account potential points of failure.
Engineers don't rely on elevator cables to never break. They design elevators to stop themselves in the event of a fall. You're telling me that your hypothetical designer doesn't know as much as an Otis engineer?
I have read both sides of the argument.
Both sides of what argument? The human retina is upside-down. The light sensitive cells are at the bottommost layer, under/behind the structural cells and circulatory capillaries.
If it was right-side up, you'd be able to see in the dark a lot better. There's no advantage to an upside-down retina. I don't understand what "other side" you think you've heard, because there is no other side. There's just the fact that human retinas are upside-down, and they either evolved that way, or were designed that way.
Evolution makes sense, because the retina still works well enough the way it is that it's not maladaptive. The design hypothesis is just incoherent. It offers no explanation except "obviously, it's supposed to be that way for reasons we don't understand."
Take my word for it. We don't reject your ideas about a designer because we hate God and all that is good and holy. We reject them for the simple reason that your explanations don't make sense. They don't allow for useful predictions. They just don't take us anywhere, or help us make sense of the universe.
Evolution does all that. That's why creationists in the 1800's came up with it - they were better scientists and more honest than any of you creationists today.

This message is a reply to:
 Message 54 by CrackerJack, posted 06-01-2004 9:36 AM CrackerJack has not replied

Replies to this message:
 Message 73 by arachnophilia, posted 06-09-2004 3:02 AM crashfrog has not replied
 Message 76 by Dr Jack, posted 06-17-2004 11:15 AM crashfrog has not replied

  
fnord
Inactive Member


Message 68 of 284 (112457)
06-02-2004 4:05 PM
Reply to: Message 54 by CrackerJack
06-01-2004 9:36 AM


But that is still much better than any human built machine, and no comparison to something a junior highschool student could build.
But not as good as you'd expect from a God.

This message is a reply to:
 Message 54 by CrackerJack, posted 06-01-2004 9:36 AM CrackerJack has not replied

  
Brad McFall
Member (Idle past 5033 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 69 of 284 (112480)
06-02-2004 7:23 PM
Reply to: Message 1 by CrackerJack
05-29-2004 11:59 PM


when is a ring inside Gould's straint but outside GG's time?
That a tough one. I am still thinking on it.
A neat case would be a symmetrical grade CAUSE for any class transition between the type herp such that snake=cecilian, lizard=salamder and frog=turtle. Things get messy in Figi once one realizes that aligators in China are not Tuatar's third eye.

This message is a reply to:
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nator
Member (Idle past 2170 days)
Posts: 12961
From: Ann Arbor
Joined: 12-09-2001


Message 70 of 284 (113563)
06-08-2004 9:09 AM


There's a very good chance that CrackerJack has run away.
Too bad, he seemed pretty smart.
Hey, B2P, keeping track of how many Creationists run away because they wish to remain ignorant of the evidence?

Replies to this message:
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1.61803
Member (Idle past 1504 days)
Posts: 2928
From: Lone Star State USA
Joined: 02-19-2004


Message 71 of 284 (113713)
06-08-2004 11:19 PM
Reply to: Message 70 by nator
06-08-2004 9:09 AM


I am beginning to suspect perhaps some Creos go on quote mining sabbaticals and return in congnito newly armed.

This message is a reply to:
 Message 70 by nator, posted 06-08-2004 9:09 AM nator has not replied

  
jar
Member (Idle past 394 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004


Message 72 of 284 (113715)
06-08-2004 11:27 PM
Reply to: Message 70 by nator
06-08-2004 9:09 AM


Or that just stick around saying the same thing even after it's refuted and refusing to answer questions. It's sad.

Aslan is not a Tame Lion

This message is a reply to:
 Message 70 by nator, posted 06-08-2004 9:09 AM nator has not replied

Replies to this message:
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arachnophilia
Member (Idle past 1344 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 73 of 284 (113757)
06-09-2004 3:02 AM
Reply to: Message 67 by crashfrog
06-02-2004 2:40 PM


There's no advantage to an upside-down retina.
isn't that statement more in favor of "stupid design" ?
i think should propose that theory, that some finitely-wise demi-god designed everything, badly.

This message is a reply to:
 Message 67 by crashfrog, posted 06-02-2004 2:40 PM crashfrog has not replied

  
Brad McFall
Member (Idle past 5033 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 74 of 284 (113869)
06-09-2004 11:30 AM
Reply to: Message 72 by jar
06-08-2004 11:27 PM


Jar, I would like to thank you for recognizing my signature etc and will continue to point out, without break, that the issue of BODY SYMMETRY as per Sharf's nice pics etc etc that this issue seems to be a matter of the difference of FORMATIVE IMPULSE vs FORMATIVE POWER where any asymmetry is (or would be if I was followed) due to an overwhelming of the impulse IN THE POWER of the formationing.
So while someone might think there are some intersting CONSEQUENCES for sticky web vs the spider that spins it non-sticky the recent induction of the existence of ecological inheritance (in "Niche Construction") seems not only to violate something Maxwell wrote but also SO THAT A PART FROM THE NOVELTY INTRODUCED in the science of biological change PROPS up Darwin with a different (NEW SIC!) casaulity that Kant held out between blind chance and teology not diffderent INFLATIONS in the students cost to appreaciate any depreciation of actual entropy calculations. It all depends on how much investment of semantics is possible the appearence but then without a thing in itself it appears that even Gladyshev's NONCREATIONIST CLASSICS can not be afforded to the same class of students, at least not those PAYING at the present elite US insitutions WHERE indeed the symmetry is not missed for alegbra it might entail. The cuprit IS LESS CREATIONISM than the failure to clearly cognize Gladyshev's clear statement to me (I mean it is in public print) that S' is NOT S and that along with anthother reviewer of ENTROPY (the journal) Dissemination Kinetic Entropy of Prigogine is NOT WITH the 2nd LAW.
In order to follow all of this past paragraph it would be much easier just for arguments sake to accept that the impulse is thermal contact and the power the thermal current for showing the DOUBLE faulty reasoning in the use Maxwell's demon I probably can not express here on EVC before you all start saying I am crazy- the Brad McFall zone- etc etc etc.
SOOOOO perhaps it is not in the formation I said but it would cost a lot less to educate biologists if people just learned what I was saying. Sure I perfer to look at sticky web than talk about the pest it has become but that is not what communication is for NOR IS IT FOR LEISURE SCIENCE. For it MAY indeed have to be here in US where we ALREADY HAVE WRITTEN in the power of this people that we might hope for humanity to our chimps that do not HAVE language or Charoltte's Web for that reason.

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Saviourmachine
Member (Idle past 3554 days)
Posts: 113
From: Holland
Joined: 01-16-2004


Message 75 of 284 (116020)
06-17-2004 11:10 AM
Reply to: Message 1 by CrackerJack
05-29-2004 11:59 PM


Why symmetry
Sorry, maybe every point is already mentioned, but I've four things why symmetry can exist in combination with evolution:
  • If a mutation for the left side is selected for, the same mutation for the right side is probably also beneficial.
  • Genetic material probably codes for both sides of the body at the same time.
  • Not only for our swimming ancestors, but also for our flying companions and for us - walking - will symmetry easify movements.
  • To keep balance.

This message is a reply to:
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Replies to this message:
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