|
Register | Sign In |
|
QuickSearch
EvC Forum active members: 65 (9162 total) |
| |
popoi | |
Total: 915,817 Year: 3,074/9,624 Month: 919/1,588 Week: 102/223 Day: 13/17 Hour: 0/0 |
Thread ▼ Details |
|
|
Author | Topic: How can evolution explain body symmetry? | ||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: Language in humans evolved to be processed in the left hemisphere of the brain. This is an asymmetry that is shared by nearly all humans today. Your premise is shown to be false.
quote: That is an unwarranted, giant non sequitur. I found the following information in about 2 minutes after doing a quick google on "asymmetrical animals". Maybe you forgot to try to find out if there actually were asymmetries before declaring that there weren't?
quote: It's not all that common.
quote: Why would this trait be selected for? We do see some selection for polydactylism in cats, because more digits with claws on them results in better ability to catch prey, as long as the number of "extra" toes doesn't encumber or endanger the cat before it can reproduce.
quote: But we do see such creatures. Crabs and lobsters tend to have one claw that is larger than the other. In some crabs, this is extremely pronounced, which is used to communicate with other crabs.
Flounder and other flat fish are quite asymmetrical, because they have evolved to lie flat on the ocean floor.
Sponges have no axis in their body plans.
Snail shells coil either to the right of left. One ear on an owl is set higher than the other so they can pinpoint sounds better. A bit more can be found here:
BBC - 404: Not Found
This message has been edited by schrafinator, 05-30-2004 11:14 PM
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
What is so special about symmetrical mutations that makes them beneficial and asymmetrical mutations not? Vertebrates all evolved from water dwelling, swimming creatures, and there is VERY good reason for a swimming creature to be symmetrical. Once the symmetry is established, why do you expect it to be abandoned so much? And of course, when there's a good reason, it is abandoned (see the pics in previous post).
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: 1) Many creatures are not extrenally symmetrical, as I illustrated. 2) Why do you discount internal asymmetry as evidence of evolution producing asymmetry? Internal structures evolve in exactly the same way as external, so it makes no sense for you to treat them differently. 3) Evolution has been shown to proceed by random processes combined with selection, but the selection is done by the environment. No intelligent "designer" needed.
quote: No offense, but your own personal observations are statistically meaningless. We call such information "anecdotal evidence", and it is quite unreliable, because your sample size is tiny and non-random.
quote: I have a mutation that caused both of my lower wisdom teeth to never develop, and that was symmetrical. A woman my husband knew in high school has corckscrew-like pinky fingers and that is symmetrical. Polydactylism in cats is symmetrical.
quote: You have made a factal claim here. Please provide reliable evidence to support it.
quote: If by "animals", you mean "vertebrates", I have already explained that all vertebrates evolved from sea-dwelling creatures, so therefore follow the same basic body plan.
quote: Exactly, but not in all cases, as my photographs showed you.
quote: Right. All the asymmetries I showed are adaptive. You seem to think that non-adaptive assymmetries (you limit your requirement to only in humans and only external, for some strange reason) should be widespread in a population. Evolution doesn't make that prediction.
quote: All animals exhibit clear assymetry, you just want to ignore the internal ones. Why do you insist that we ignore internal asymmetry?
quote: That is exactly what I am saying. There are, however, evolutionary pressures to cull out most asymmetries.
quote: We still have them. They are mostly internal. Why do you ignore them? As for external symmetry in humans, it has been empirically shown that symmetry is strongly sexually selected. IOW, asymmetry reduces a human's chance of mating.
quote: 1) Evolution does select them out, which is why we don't see them. 2) We have plenty of asymmetries, they are just internal. Why don't they count to you?
quote: You're right, it is absurd. That's why the above is not what evolution says. There is nothing in the ToE which requires only one beneficial mutation to become dominant in a population before another occurs. If this were true, the entire human population would be genetically identical.
quote: But they are here. Humans are FUNDAMENTALLY asymmetrical in nearly all respects EXCEPT for basic body plan, alterations to which are likely to strongly negatively affect either locomotion, sexual attractiveness, or both.
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: But once you set up embryonic development in which all vertebrates are symmetrical in their basic body plan, how long do you think it should take to change it, particularly since there is no great evolutionary pressure to be asymmetrical? Furthermore, creatures ARE fundamentally asymmetrical, except for basic body plan, alterations to which may detrimentally affect sexual attractiveness and locomotion.
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: Why should this happen "very often"? Also, please define "very often"; how often is "very often?".
quote: Alterations to the external body may reduce sexual attractiveness and may impede locomotion.
quote: Actually, mutations affecting basic body plan do strongly tend to affect the individually symmetrically, because that is how embryonic development occurs.
quote: No, plants and animals are not fundamentally different life forms. Fundamentally, they are the same. The same system of DNA and RNA is found in both plants and animals. Why does it matter, anyway?
quote: NO IT DOESN'T! Evolution does not predict that every single creature be symmetrical. Nor does it predict that every single creature be asymmetrical. It predicts that populations will, over time, adapt to their environments or go extinct.
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: If you can't make any testable predictions about how the designer might design something, the ID is useless as science. Also, you have been saying all along that suchandsuch is evidence for a designer, but now you say it is impossible to know what or how the designer designed anything. Which is it? Do you know, or is it impossible to know? This message has been edited by schrafinator, 05-31-2004 10:09 AM
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: Symmetry is useful for walking on land, too. Try walking with one leg shorter than the other. Also, Why do you think that asymmetrical mutations should have become dominant long ago if they are not adaptive?
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: No, but if it had one leg a lot shorter than the others, it would have a pretty hard time of it.
quote: No, but it may impede your ability to grasp and hold things in your hand, like food, weapons, tools or prey. Hands, BTW, are unique to certain primates. They are an extremely recent evolutionary development. Potential mates would probably be less likely to be attracted to you due to your birth defect, too.
quote: One leg is shorter than the others. One foot is larger than the others. Your big toe is tiny on one foot and big on the other. You are under some mistaken impression that a mutation has to cause a creature to not be able to walk at all to be tetrimental. My husband is bow legged and flat footed, which is fine now because he is an academic, but a million years ago, on the savannah, he would be at a pretty big disadvantage.
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: Right. This is because we evolved from aquatic creatures in which symmetry is very advantageous. Symmetry continues to be advantageous in MOST cases.
quote: Why? You can't see the inside of other creatures, so sexual selection in favor of internal symmetry cannot happen.
quote: You have shown it? Where?
quote: Really? Are you typically sexually attracted to people with significant facial deformities? That makes you pretty rare.
quote: When your basic body plan is externally symmetrical from embryonic development, and external symmetry is sexually selected for, why do you expect asymmetry to become widespread at all?
quote: At last, you are doing some research. Now, perhaps you might consider doing all of your research before you make exterme claims instead of after.
quote: So? The ToE doesn't say that it has to be.
quote: That's what we've been saying all along, you know.
quote: Why?
quote: Why?
quote: Why? Where is the selection pressure for asymmetry?
quote: Why?
quote: Why? Where is the selection pressure for asymmetry?
quote: SEXUAL SELECTION and LOCOMOTION selects in favor of external symmetry, as well as our basic body plans being derived from sea-dwelling creatures in which external symmetry was also highly advantageous.
quote: Why? It might not be a disadvantage at all. In fact, for it to become fixed in a population, it would have to tend to be advantageous in some way, to some population.
quote: Since we already sexually select FOR external symmetry, an obvious external asymmetry is not likely to become widespread in the first place.
quote: Actually, our ability to reason is why people with facial deformities and other external asymmetries are able to get mates. Unlike animals, we are able to be attracted to a personality and overlook the physical. Anyway, why do you think that animals don't reject deformed offspring or potential mates? My friend's cat just had kittens, and there was a malformed one in the litter. The mother ate it.
quote: Why? Why would it be selected for in the first place?
quote: The majority of selective pressures favor external symmetry. A minority do not.
quote: They are less likely to reproduce, thus they do not pass on the mutation.
quote: They are, in the form of failed implantation, reabsorbed, miscarried, and stillborn offspring, etc.
quote: No, that's why we see them today.
quote: The opposable thumb isn't human in origin. We got that from our primate ancestors. Anyhow, haven't you been reading what we have been telling you about how embryonic development occurs?
quote: Like what?
quote: Because they are actively selected against due to our preference for external symmetry in mates, mostly. If they conferred an advantage in some way, though, we'd still have them.
quote: I haven't seen this. Where have you done this? Did you know that there are many studies which show that symmetry of facial features is the most important factor in someone finding a face attractive?
quote: Don't be silly. You don't have to see and you don't have to be able to count to tell if another of your species is symmetrical or not. And, symmetry is not as important in other creature's sexual habits as ours, anyway.
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: If you reject all evidence for evolution (of which there is a VERY GREAT DEAL more that the tiny bit we have been discussing here), then you have to explain what we see with another scientific theory. That theory must have positive evidence to support it, make testable predictions, and be falsifiable.
quote: You cannot make a scientific claim based upon a lack of evidence. Nor can you make a scientific claim based upon another theory's faults or shortcomings. Nor can you make an Argument from Personal Incredulity. Nor can you make a God of the Gaps argument. OK, you CAN make all of these claims and arguments, but none of them are valid arguments. Here is a question for you... How can we tell the difference between an Intelligently Designed system and a natural one that we; 1) don't currently understand but may in the future, and/or 2) may not ever understand?
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: 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: Since we are discussing science, your personal perspective is irrelevant.
quote: 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: 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: 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: That's rich! You have basically claimed that every example of symmetry AND every example of asymmetry proves your point.
quote: 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: It has been shown in many animals. Why do you require that it be all?
quote: 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.
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
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?
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: There exists a mass of evidence to indicate that indoctrination has occured: folk are told that the Earth is a sphere is a fact for from their formative years upwards, long before they have been equipped (if ever they truly could be) to establish the facts for themselves. Note: whether the indoctrination is ultimately true or false matters not. It's still indoctrination.
quote: Tell me, just what do you think the practice of science was like in Darwin's day? What was the leading professional journal, for example? What were the PhD requirements?
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: How about children being indoctrinated in the idea that the Earth is a sphere long before they have the ability to examine the data for themselves?
quote: What is a physics "lecturer"? Does he have a degree in Physics?
quote: Almost without fail, such qualified people in those fields who do not accept the evidence for Evolution do so upon a religious, not scientific, basis. Scientific advancement progresses through consensus. For an idea to become widely accepted, it must survive many repeated tests by many disinterested parties. IOW, it has to be useful, and it has to be consistent. The theory of evolution has survived, and so we accept it tentatively as the best current explanation of the change in alleles in populations over time.
|
||||||||||||||||||||||||||
nator Member (Idle past 2170 days) Posts: 12961 From: Ann Arbor Joined: |
quote: Your father is a physics lecturer and he hasn't taught you anything about gravity? How long, exactly, has your father been studying Physics?
|
|
|
Do Nothing Button
Copyright 2001-2023 by EvC Forum, All Rights Reserved
Version 4.2
Innovative software from Qwixotic © 2024