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I have a question that maybe the folks here can help me with. In school the focus of the study of evolution is on how animals evolve. Do plants evolve the same way? Is there any evidence (fossil record) of plant evolution? Or is the process confined to us animals?
Is there any evidence that animals evolve? (That is beyond small variations within the same genus).
I would say no. I word I use for what you said is adaptation. From what I have heard, though, is that there is nothing that could even be construed as evolution in the plant kingdom. There are things out there that people could construe as evidence of animal evolution, but if there is absolutely no evidence pointing to plant evolution then where did they come from? I guess that is all I am asking.

Brian
Quote:I word I use for what you said is adaptation

I would not. The reason is that many cases of genetic variety have little or nothing to do with adaptation; for example, the original Darwin's observation about different types of birds on different islands was not an example of either evolution or adaptation. Genetic variety in fresh-water fish in different river systems is again not adaptation. While adaptation most certainly exists, it is not clear at all what %-age of genetic divergence is attributable to it.

As for plants, there is no evidence of evolution either.

However, your question was actually a good one. While it is easy to see why, for example, mammals could not possibly not evolve from fish, I don't have an immediate easy argument why trees could not evolve from moss (does not mean that one does not exist, of course).
Oculus Wrote:...the focus of the study of evolution is on how animals evolve. Do plants evolve the same way?

Theory of evolution treats all living beings in the same way. Bacteria, plants, animals, it's all the same on the DNA replication level. And comparison of DNA of extant species is used to reconstruct phylogeny rather than comparing fossils. This method has some limitations, but appears to be the best thing so far.

Oculus Wrote:Is there any evidence (fossil record) of plant evolution?

Sure. Coal is the most abundant. But classic fossils are found as well.
[Image: fossilplants-200.jpg]

As far as I know, phylogenetics of plants is still less known than of animals, genome projects are focused on animals at the moment. Currently phylogeny of plants therefore mostly sits on a comparison of a small number of genes.

mv Wrote:While it is easy to see why, for example, mammals could not possibly not evolve from fish

Double negation. Man.

mv Wrote:As for plants, there is no evidence of evolution either.

Well, there is (same as for animals), but just on a microevolution scale. Anything going on above subspecies level is a theory. So far, it seems to be a good theory.
COS Wrote:Sure. Coal is the most abundant. But classic fossils are found as well.

I have seen fossils of plants before.....and they look the same then as they do now. I admit that I am no scientist, but I am curious. The only thing these fossils do is prove that plants existed a long time ago. They do not show a flower evolving into a tree over eons of time.

COS Wrote:And comparison of DNA of extant species is used to reconstruct phylogeny rather than comparing fossils.

Please explain this to me. How do we decide what the DNA of a plant from many years ago looked like by looking at DNA from plants today. Wouldn't that be mere speculation?

When studying the theory of evolution they always show, "here is how this microbe evolved into this tadpole-thingy, then into this fish, then into this frog etc, etc." but I have never seen anyone show the series involved in plant evolution. What did an oak tree evolve from? Either it had to evolve from something or is spontaneously appeared.
Oculus Wrote:
COS Wrote:And comparison of DNA of extant species is used to reconstruct phylogeny rather than comparing fossils.

Please explain this to me. How do we decide what the DNA of a plant from many years ago looked like by looking at DNA from plants today. Wouldn't that be mere speculation?

Speculation? Not entirely, some things can be tested, but in the absence of time machines, speculations, as you call them, are the only thing we have. Science theories are all build on a certain number of assumptions. A good theory has less assumption and can explain most of things. Preferably all.

So to explain more about this. Phylogeny is based either on fossils or on DNA. In the case of DNA, you don't care what plants looked like ages ago. Forget it. You take a gene that can be found in all plants and is conserved (low mutation rate). You collect samples of an oak, rose, pine tree, moss, the more the better. You isolate DNA from all samples and sequence the gene in all of them.

And then you put all these sequences in a computer program that calculates a phylogenetic tree from these sequences. There are several different concepts of calculating this kind of tree. The easiest way to explain the principle is that 2 sequences that have less differences are placed more closely, they are more closely related.

The assumption made here is that when you compare many conserved sequences, the phylogeny of sequences will correspond phylogeny of species. The most difficult thing here is to chose an appropriate sequence to study (present in all species, low mutation rate, no horizontal transfer and other things).

There are some things here that are tricky to explain, I am trying to simplify it.

from here
Quote:Molecules and fossils, with their different strengths and weaknesses, are best viewed not as competing forces or equal characters to be blended but rather as complementary sources of information for evolutionary history.
Quote:
mv Wrote:While it is easy to see why, for example, mammals could not possibly not evolve from fish
Double negation. Man.

My bad. Take out one not. "not possible evolve".
The first fish that, due to some mutation, could breath air (even for a short time) and enjoyed it probably was considered a freak by fellow fishes. :lol:
ag Wrote:The first fish that, due to some mutation, could breath air (even for a short time) and enjoyed it probably was considered a freak by fellow fishes. :lol:

Actually, I did not mean breathing air. This is no big deal, as it happens a number of current fish species can do it. For example, Gouramis, which is a large family of tropical fresh water fish, do this; so you can keep them in a tank without much oxigen in the water. I suspect that there are a number of other unrelated families that can do this too, and that the *ability* may be "programmed" but inactive in most fish. (Darn useful ability in limited and less stable freshwater environments).

(What goes below is not the proof I promised last summer, but a related weaker argument).

The big deal is the sex selection. Some factoids: while the mammals use the XY/XX scheme, this is not what the fish have; in fact it is generally unknown what are the schemes. (Asacr, some seem to follow the reptile scheme, which is determination based on temperature). The problem is that you cannot switch from one mechanism of sex determination to another, there is a point of discontinuity, where you need to see the same mutation appearing in both parents.

This is what kills evolution. Wink1
mv Wrote:The problem is that you cannot switch from one mechanism of sex determination to another, there is a point of discontinuity, where you need to see the same mutation appearing in both parents.

This is what kills evolution. Wink1

You went deep in genetics and I find it hard to provide a short answer. It doesn't kill evolution. In short, there are some (if not only 1) "sex determining" genes, these regulate the expression of a larger number of genes all over genome. There are different mechanisms about how they are activated/suppressed. In some reptiles and fish, this is regulated by temperature. So, XY can be either male or female, same for XX.

The difference between a temperature regulated sex and purely chromosome determined sex is just in the loss of temperature regulation. So, a minor mutation that alters the sex determining gene, enough just in one parent, that can be passed on to offspring, and original gene subject to temperature regulation lost from the gene pool in the following generations can result in a purely XY/XX determined sex.

Killing evolution is not an easy task.
Not so quick.

Quote:There are different mechanisms about how they are activated/suppressed. In some reptiles and fish, this is regulated by temperature. So, XY can be either male or female, same for XX.

Yes, but there are no XX/XY in temp. regulated species.

Quote:and original gene subject to temperature regulation lost from the gene pool in the following generations can result in a purely XY/XX determined sex

The problem is that there is no XX/XY determination in the offspring generation--yet. There are no XX/XY chromosomes yet.

Thus, you need two events to occur at once: old mechanism (temp. regulated) to fail and new one to form. This is difficult to imagine.
If you are right (about reptiles actually having sex chromosomes), this is a good rebuttal, there will be no discontinuity, and the picture would make sense (temp. based mechanism is likely to break down in case of massive climate changes and the incident of turning it off would be a huge evolutionary advantage).

However, there other discontinuities which are difficult to bridge.

For instance, how can you bridge the change in the number of chromosomes between species? There is a discontinuity point where the parents have N chromosome pairs, while the offsprings have M (!=N).
mv Wrote:The problem is that there is no XX/XY determination in the offspring generation--yet. There are no XX/XY chromosomes yet.

Thus, you need two events to occur at once: old mechanism (temp. regulated) to fail and new one to form. This is difficult to imagine.

Possible scenario to produce sex chromosomes:

An organism that has sex determining gene on an chromosome named X. Gene is regulated by temperature, causing that XX can be female or male.

A mutation (chromosome rearrangement) happens on one of the X (say... a loss of a 80% of the chromosome). The new variant is called Y with some remaining function in sex determination. Since one X is still completely functional, temperature still regulates sex. Y, if not a lethal mutation, is calmly passed to offspring. So, you have XX and XY, both can be male or female. Now happens the lost of temperature regulation on X mentioned above.

OK, so minimum requirements would be: one chromosome rearrangment, one point mutation.
mv Wrote:For instance, how can you bridge the change in the number of chromosomes between species? There is a discontinuity point where the parents have N chromosome pairs, while the off springs have M (!=N).

Like chimps and humans (one pair less)?

OK, providing that both N (=2n) and M (=2(n+1)) variants have otherwise all genes functioning, you have two possibilities:

1- mutant with 2n+1 number of chromosomes that can reproduce with 2n and have fertile offspring. After several generations, now more numerous 2n+1 mate and produce fertile 2(n+1) offspring

2- curiously enough, some types of chromosome rearrangements are very frequent (e.g. philadelphia chromosome). Imagine that always the same type of rearrangement occurs in such a way, that only mutants with exactly the same chromosomal rearrangement can reproduce among themselves. In this way, there is only a question of time to when two such mutants will appear in the same time and place.

added: hm, I tried to delete and rewrite one of my posts, it seems that I managed to change their order somehow.
Some holes to plug:

Quote:A mutation (chromosome rearrangement) happens on one of the X (say... a loss of a 80% of the chromosome).

Hmm,...is not is peculiar that we don't see this happening with non-sex chromosomes? In your picture, X and Y are still pretty much non-sex when this occurs.

Quote:The new variant is called Y with some remaining function in sex determination

Some remaining function: ??? Your Y either has the sex-determination gene or does not; please say which.

Quote:So, you have XX and XY, both can be male or female.

And some YY's too, therefore, I assume they all die right away? What a waste.

Quote:Now happens the lost of temperature regulation on X mentioned above.

Lost of temp regulation means that all X' are locked in one state.

Let me understand this, again:

Quote:So, you have XX and XY, both can be male or female.

We have 6 variations, assuming + means Female form of Sex-Gene activation, and Y does not have the Sex-Gene:

X+X+ -- female?
X+X- -- female?
X-X- -- male?
X+Y -- female?
X-Y -- male?

Is not this a bit too complex?
COS Wrote:
mv Wrote:For instance, how can you bridge the change in the number of chromosomes between species? There is a discontinuity point where the parents have N chromosome pairs, while the off springs have M (!=N).

Like chimps and humans (one pair less)?

Exactly what I meant. Actually, 48=(2*24) is the number for all great apes.

Quote:OK, providing that both N (=2n) and M (=2(n+1)) variants have otherwise all genes functioning, you have two possibilities:

1- mutant with 2n+1 number of chromosomes that can reproduce with 2n and have fertile offspring. After several generations, now more numerous 2n+1 mate and produce fertile 2(n+1) offspring

Prob 1: We assume that the common-ancestor was a great ape, so it is down from 48->46. Prob 2: And how is this extra chromosome passed?

Quote:2- curiously enough, some types of chromosome rearrangements are very frequent (e.g. philadelphia chromosome). Imagine that always the same type of rearrangement occurs in such a way, that only mutants with exactly the same chromosomal rearrangement can reproduce among themselves. In this way, there is only a question of time to when two such mutants will appear in the same time and place.

The answer is probably here somewhere; but I find it extremely difficult to believe that such rearrangements will repeatedly happen in the same time and place.---unless there is a mechanism that causes them. Such mechanism is currently unknown.

Quote:added: hm, I tried to delete and rewrite one of my posts, it seems that I managed to change their order somehow.

Actually, your previous (deleted) post had a stronger argument; good that you deleted it S1
mv Wrote:
Quote:A mutation (chromosome rearrangement) happens on one of the X (say... a loss of a 80% of the chromosome).
Hmm,...is not is peculiar that we don't see this happening with non-sex chromosomes? In your picture, X and Y are still pretty much non-sex when this occurs.

We do. Pretty often, chromosomal rearrangements are found in 1 out of 300 people according to what I was learned. Sex chromosome is the one that has sex determing gene(s).

mv Wrote:
Quote:The new variant is called Y with some remaining function in sex determination
Some remaining function: ??? Your Y either has the sex-determination gene or does not; please say which.

Must have some remaining, otherwise it wouldn't be called sex chromosome. See also below.

mv Wrote:
Quote:So, you have XX and XY, both can be male or female.
And some YY's too, therefore, I assume they all die right away? What a waste.

If Y is a truncated form of X, it has most genes missing. YY combination would have no working copy of some genes, yes, it would die right away before first cell division.

mv Wrote:
Quote:Now happens the lost of temperature regulation on X mentioned above.
Lost of temp regulation means that all X' are locked in one state.

Not if Y would keep "some remaining function in sex determination" as I put earlier. Totaly needless genes/chromosomes tend to get lost anyway.

mv Wrote:Is not this a bit too complex?

Please don't go intelligent design here. I am just trying to think of a possible scenario here.
Quote:Please don't go intelligent design here. I am just trying to think of a possible scenario here.

I'm not doing intelligent design (yet).

I'm only pointing out that your scenario is overly complex: if seems to require 5 reptile sexes (even if they appear as only two). And I still fail to understand what is the sex functionality in the Y chromosome within your model (human Y chromosome has some genes involved in sperm mobility, asacr).
Shit. Italy leads 1:0





mv Wrote:Prob 1: We assume that the common-ancestor was a great ape, so it is down from 48->46. Prob 2: And how is this extra chromosome passed?

When gametes are produced, one copy of each homologous chromosomes is pulled into each gamete. Extra chromosome could be passed if it is possible that it is pulled into one gamete even if it has no pair.

I don't know if that is possible.
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