Symetry

[gnx1987]

How does evolution explain symmetry? Nearly every species is symmetrical. Now just because there are a few that aren't, you can't use that as evidence because it ignores the fact that most are, and as evolution is just something based on random mutations how can it produce hundreds if not thousands of symmetrical species. Just because all species would be likely to survive better with a balanced body doesn't mean it's impossible for it to survive with an imbalanced body.

How could evolution "know" to sprout an identical body part on the exact opposite of the body? And don't give me any garbage about some body parts on people might be a little smaller or a little longer or slightly off symmetry, that's nit picking and fact of the matter is nearly identical is unlikely enough in regards to evolution.

 

[sfs]

How does evolution explain symmetry? Nearly every species is symmetrical. Now just because there are a few that aren't, you can't use that as evidence because it ignores the fact that most are, and as evolution is just something based on random mutations how can it produce hundreds if not thousands of symmetrical species.

There are millions of symmetrical species, not thousands. They're all symmetrical because they inherited that body plan from their common ancestor. (Or common ancestors -- animals with two-fold symmetry like us inherited that from one ancestor, while those with five-fold symmetry like starfish inherited that trait from a different ancestor.)

How could evolution "know" to sprout an identical body part on the exact opposite of the body?

The two sides of the body develop the same because they are produced by identical genes being expressed in the identical sequence, starting from an egg that is symmetric. (It's rather harder to develop asymmetry with this system than it is to develop symmetry.) No special mechanism is needed to make the two sides the same.

 

[AECellini]

There are millions of symmetrical species, not thousands. They're all symmetrical because they inherited that body plan from their common ancestor. (Or common ancestors -- animals with two-fold symmetry like us inherited that from one ancestor, while those with five-fold symmetry like starfish inherited that trait from a different ancestor.)

The two sides of the body develop the same because they are produced by identical genes being expressed in the identical sequence, starting from an egg that is symmetric. (It's rather harder to develop asymmetry with this system than it is to develop symmetry.) No special mechanism is needed to make the two sides the same.

this.

 

[Jamin4422]

How does evolution explain symmetry?

Symmetry was around before Evolution. It is explained by things like the Golden Ratio, Fibonacci Numbers. Some people say there is an association with gravity but that is not a popular theory right now.

 

[Trogool]

How does evolution explain symmetry? Nearly every species is symmetrical. Now just because there are a few that aren't, you can't use that as evidence because it ignores the fact that most are, and as evolution is just something based on random mutations how can it produce hundreds if not thousands of symmetrical species. Just because all species would be likely to survive better with a balanced body doesn't mean it's impossible for it to survive with an imbalanced body.

The key to the direction of evolution is the differential reproductive rate, not survival, as was stated in the first week of General Biology.

How could evolution "know" to sprout an identical body part on the exact opposite of the body?

Because populations that "do", achieve reproductive success at a higher frequency than those which do not.

And don't give me any garbage about some body parts on people might be a little smaller or a little longer or slightly off symmetry, that's nit picking and fact of the matter is nearly identical is unlikely enough in regards to evolution.

You know, in science, you actually have to be precise. "symmetry" isn't "symmetry with 10 centimeters of error".

 

[USincognito]

Hox gene - Wikipedia, the free encyclopedia

 

[Wiccan_Child]

There are millions of symmetrical species, not thousands. They're all symmetrical because they inherited that body plan from their common ancestor. (Or common ancestors -- animals with two-fold symmetry like us inherited that from one ancestor, while those with five-fold symmetry like starfish inherited that trait from a different ancestor.)

The two sides of the body develop the same because they are produced by identical genes being expressed in the identical sequence, starting from an egg that is symmetric. (It's rather harder to develop asymmetry with this system than it is to develop symmetry.) No special mechanism is needed to make the two sides the same.

Nothing I can say trumps this, so ^^^ this ^^^

 

[juvenissun]

There are millions of symmetrical species, not thousands. They're all symmetrical because they inherited that body plan from their common ancestor. (Or common ancestors -- animals with two-fold symmetry like us inherited that from one ancestor, while those with five-fold symmetry like starfish inherited that trait from a different ancestor.)

The two sides of the body develop the same because they are produced by identical genes being expressed in the identical sequence, starting from an egg that is symmetric. (It's rather harder to develop asymmetry with this system than it is to develop symmetry.) No special mechanism is needed to make the two sides the same.

This is new to me (quite common). I assume the arrangement of genes is linear. So how do they control the symmetry in another dimension?

 

[NailsII]

How does evolution explain symmetry? Nearly every species is symmetrical. Now just because there are a few that aren't, you can't use that as evidence because it ignores the fact that most are, and as evolution is just something based on random mutations how can it produce hundreds if not thousands of symmetrical species. Just because all species would be likely to survive better with a balanced body doesn't mean it's impossible for it to survive with an imbalanced body.

How could evolution "know" to sprout an identical body part on the exact opposite of the body? And don't give me any garbage about some body parts on people might be a little smaller or a little longer or slightly off symmetry, that's nit picking and fact of the matter is nearly identical is unlikely enough in regards to evolution.

Let's not get too far ahead of ourseves here - we may look like we are bilaterally symmetrical, but we are not exactly - only in general.
You have a heart which is touching your left lung, but not your right.
You have one liver which is not central; one spleen, the intestinal tract is not symmetrical - and your brain most certainly is not.
You may also note that your arms and legs can be measurably different lengths.

Evolution doesn't 'know' anything, it just 'does'.
If it works, (ie is reproductively successful, it carries on.

This is new to me (quite common). I assume the arrangement of genes is linear. So how do they control the symmetry in another dimension?

From someone wo claims to understand evolution, you have a very, very poor knowledge of biology.

Proteins are transcribed from genes, the DNA (or RNA) sequence is indeed two dimensional.
Proteins form 3-D shapes - such is the nature of the protein.
They can form weak or strong bonds to maintain these shapes, which can vary according to pH or temperature.

 

[Wiccan_Child]

This is new to me (quite common). I assume the arrangement of genes is linear. So how do they control the symmetry in another dimension?

Because one gene says "this is an arm", another says "put a gene at the shoulder joint, a leg at the hip, and both in this arrangement with the torso", and a final gene says "double everything".

It's like crystals. One arm on a snowflake doesn't know what the other arm is doing, but because they both obey the same rules and operate in the same conditions, they end up doing the same thing.

And as for the linearity and multi-dimensionality of genetic expression... you're thinking too literally - but you're a Creationist so that's understandable .

 

[juvenissun]

Proteins are transcribed from genes, the DNA (or RNA) sequence is indeed two dimensional.
Proteins form 3-D shapes - such is the nature of the protein.
They can form weak or strong bonds to maintain these shapes, which can vary according to pH or temperature.

So, what is the symmetry content of DNA? How does it develop a m/2 symmetry of most lives?

 

[juvenissun]

Because one gene says "this is an arm", another says "put a gene at the shoulder joint, a leg at the hip, and both in this arrangement with the torso", and a final gene says "double everything".

It's like crystals. One arm on a snowflake doesn't know what the other arm is doing, but because they both obey the same rules and operate in the same conditions, they end up doing the same thing.

And as for the linearity and multi-dimensionality of genetic expression... you're thinking too literally - but you're a Creationist so that's understandable .

Your explanation is good for kid.

I am trying to understand what sfs said: "The two sides of the body develop the same because they are produced by identical genes being expressed in the identical sequence, ". I can not picture what do those genes look like.

 

[The Engineer]

So, what is the symmetry content of DNA? How does it develop a m/2 symmetry of most lives?

Do you even bother to read what people write you?

There is no symmetry content of DNA! Not the way you picture it, at least.

I thought Wiccan Child's explanation was very good.

Your explanation is good for kid.

Considering you know little more about this than a kid, that's only fair.

I am trying to understand what sfs said: "The two sides of the body develop the same because they are produced by identical genes being expressed in the identical sequence, ". I can not picture what do those genes look like.

Two identical sets of genes work at two sides of the body. Guess what emerges? Symmetry. Two sides, built using the same blueprint and the same material. Symmetry is the only thing that can emerge out of this.

 

[NailsII]

So, what is the symmetry content of DNA? How does it develop a m/2 symmetry of most lives?

As large portions of our body are not symmetrical, I don't see how your question has any meaning.

Embryology explains the overall symmetry, maybe you should add that to your 'must read' set of subjects.

 

[gnx1987]

There are millions of symmetrical species, not thousands. They're all symmetrical because they inherited that body plan from their common ancestor. (Or common ancestors -- animals with two-fold symmetry like us inherited that from one ancestor, while those with five-fold symmetry like starfish inherited that trait from a different ancestor.)

The two sides of the body develop the same because they are produced by identical genes being expressed in the identical sequence, starting from an egg that is symmetric. (It's rather harder to develop asymmetry with this system than it is to develop symmetry.) No special mechanism is needed to make the two sides the same.

Obviously that's how it's done now. But how did symmetry first occur when there was nothing directing it. And if it was because of genes or dna or whatever, how did that start deciding symmetry?

 

[gnx1987]

You know, in science, you actually have to be precise. "symmetry" isn't "symmetry with 10 centimeters of error".

I don't know know anyone who has an ear that is out by 10 centimeters. If you cut someone in half, both halves would look identical unless you went and measured the location of every part.

 

[sfs]

I am trying to understand what sfs said: "The two sides of the body develop the same because they are produced by identical genes being expressed in the identical sequence, ". I can not picture what do those genes look like.

The genes just produce proteins when they're turned on. What turns them on is a cascade of signalling molecules in the developing embryo, starting with the fertilized egg. That's where the symmetries of the body plan are generated, not in the DNA for the genes. Roughly speaking, there is a gradient of a signalling molecule across the embryo. At the center of the embryo, the level of a signal is high enough that genes responsible for starting limb formation are turned off. Toward the edge of the embryo, they're low enough that those genes can be turned on -- provided other switches controlled by other signalling molecules say they should be. Those other signals tell how close the cells are to the head of the embryo, and whether they are near the front or the back, and probably lots of other things that I don't know about.

(Note: this is a cartoon version from someone who does not know developmental biology at all well. But that's the basic idea.)

 

[gnx1987]

Let's not get too far ahead of ourseves here - we may look like we are bilaterally symmetrical, but we are not exactly - only in general.
You have a heart which is touching your left lung, but not your right.
You have one liver which is not central; one spleen, the intestinal tract is not symmetrical - and your brain most certainly is not.
You may also note that your arms and legs can be measurably different lengths.

But random can't create symmetry. Flip a coin just 10 times and the second 5 results aren't going to mirror the first 5. And evolution has loads more room for error.

 

[gnx1987]

Because one gene says "this is an arm", another says "put a gene at the shoulder joint, a leg at the hip, and both in this arrangement with the torso", and a final gene says "double everything".

It's like crystals. One arm on a snowflake doesn't know what the other arm is doing, but because they both obey the same rules and operate in the same conditions, they end up doing the same thing.

But how can these rules come from something that is random?

 

[Wiccan_Child]

But how can these rules come from something that is random?

Short answer: natural selection.

Long answer: random variation in the genes that organise basic body shape will, naturally, alter the body plan. If these alterations are better than the original, then those genes will be more likely to be passed on.