Macroevolution Observed?

soyou are saying that the macroevolution of the fish causes the level of the lake to drop thus magically seperating the two species into the two remaining bodies of water -- magically because not one of either species gets left in the wrong lake ...faxcicanating ...I've heard of magic koalas before, and now magic fish.wonderful.

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist

The usual hypothesis to explain how the populations become seperated is to start with geographic isolation. Given such a barrier the populations will diverge and if the isolation continues for long enough then they will diverge to the point where the two populations cannot interbreed. (An example where his appears to have almost happened is the salamander Ensatina - all of the subspecies of this "ring species" can interbreed with some of the others, but not all combinations are interfertile).So we have a seperation that happens before any evolutionary change. Once the seperation is in place you can get changes between the seperated groups that could not happen within an interbreeding group.In all cases the basic seperation happens first, and THAT leads to macroevolution. There is then no circularity and no difference in the processes involved - just circumstances that prevent the populations from successfully interbreeding.

You've almost put your finger on it here. The term "macroevolution" is a description of the result of large scale change in two populations. Macroevolution is NOT a cause - the cause is reproductive isolation of two populations. They don't even have to be necessarily physically separated - the isolating mechanism can be behavioral or sexual, temporal, habitat isolation (the geographic separation you and Paulk have been discussing), etc. It really doesn't matter how the incompatibility arises. The point is that speciation occurs when something happens to two populations - whether they're in contact or not - that causes them to diverge to a (relatively arbitrary) point where gene flow between the populations is minimized or eliminated. Once isolation occurs, divergence is inevitable as each population continues on its own evolutionary trajectory. Ultimately, over time more and more variance is seen in these two groups as the isolating mechanism (whatever it is) continues to operate and the separate populations are subjected to their individual selection pressures. The more divergeance, the greater the possibility that some "new" structure - like your sexual apparatus - is derived.Hope this helps.

Paul K
"The usual hypothesis to explain how the populations become separated is to start with geographic isolation."(You're basically making a proposition which is always true and somewhat "tautological", since it's pretty obvious that to isolate something is to separate it from something else.)"Given such a barrier the populations will diverge ( they will diverge because they are separated?) and if the isolation continues for long enough then they will diverge to the point where the two populations cannot interbreed.(And THIS is the question, WHAT is causing the divergence? Is it the geographic isolation or is it Macroevolution (which makes the interbreeding with the separated population impossible.) You're still confusing two ideas into one. Which is it, the "barrier" or "time", respectively the "geographic isolation" (which is a given barrier) or "Macroevolution (which requires time)? Or are you applying divergence to mean BOTH geographical isolation AND Macro changes. Divergence means what to you, their inability to interbreed anymore based on a Macro change or their inability to interbreed anymore based on a separation via geographical isolation. Which is causing the divergence?)"So we have a separation that happens before any evolutionary change. (Ok?) Once the separation is in place you can get changes between the separated groups that could not happen within an interbreeding group.""In all cases the basic separation happens first, and THAT leads to macroevolution."And HOW exactly does the separation lead to Macro? See here's the problem. I know what you guys are trying to say here that if you split ,or diverge, group A into 2 groups that each specific separated group will have (macro) changes occur that eventually makes it impossible for them to inerbreed if they were reintroduced later. But it's the CHANGES WITHIN those Separated Groups that is the issue. What you guys don't realize is that there's a smoke screen occurring because the idea of "separation first, leads to macro" still does not explain how a Large Change like Macro occurs. Just splitting the groups does not a Macro change make. However if you were to say that a Macro change happened FIRST which THEN CAUSED the separation or divergence then we're getting somewhere and we get back to my initial problem. But just to say that a group separated itself geographically first which then brought about macro changes avoids the real issue of how it is that in EITHER group a Macro change occurred.The separate circumstances are irrelevant to the question. Which is, again, WHAT CAUSES Macro changes? Putting a group in an isolated circumstance doesn't explain, show or otherwise make evident that Macro changes either Have, or Will occur.?

It seems that you're just not getting it. You assumed that there had to be macroevolution before populatiosn stopped interbreeding. I pointed out that geographic isolation can ALSO stop interbreeding.And then we're back to the fact that if there is no interbreeding between the populations then evolution is going to cause divergence.And divergence is how you end up with two species instead of one.If anyone is putting up any sort of smoke screen it's you. Maybe you're just confused in which case I repeat my suggestion that you actually think about the issues.

The thing I think you're missing is that macroevolution isn't an event, it's a result.To illustrate, let's count to ten. 1,2,3,4,5,6,7,8,9,10. Simple, right? Tiny little steps each time, right?Now, where in that sequence did we go from one to ten? We did, right? We started with one, and now we have ten. That's a big change, so where did it happen? The answer is that going from one to ten isn't an event of counting, it's a result of counting.Macroevolution is the result of a process that starts with reproductive isolation and is driven by incremental change over time. Eventually the accumulated change is sufficient that there are two separate species where before there were one. It's macroevolution, apparently, when the two groups pass some arbitrary measure of different-ness. (This ambiguity is why biologists don't generally use the term macroevolution; it's not very descriptive.)

That's very odd. Milagros replied to my post, but answered yours. I'm so confused...

Quetzal:
"The point is that speciation occurs when something happens to two populations"That's exactly what I am trying to get at. That "SOMETHING".
I can only assume that that "something" is Macroevolution because it's the "something" that causes the separate populations to no longer be able to interbreed (which happens to be one of the definitions used to define one species from another). But you can't say that the initial "separation" was the "something" that caused the divergence, THEN turn around and say the "Macro change" was the "something" that caused the divergence. These are 2 different ideas and what's happening is that they are being looked upon as 1 idea or they are trying to be infused to mean the same thing. You get what I'm saying here? Basically what made the new species (what diverged them?), the fact that they were separated or the fact that macro occurred?If you simply say it was the separation causing the divergence itself that doesn't explain Macroevolution per se at all. If you say Macro caused the divergence THEN the question is how can Macro include things that CANNOT happen to Micro changes (which was my initial question based on what the paragraph I cited stated)?

What it means it that populations which are sepparated has different things happening to them. Any changes in one of the new populations *can not* be moved to the other, since they can't interbreed.So, in the start, the differences are very small. Changes will affect only one of the two groups, so as time passes, you'll see more and more distinct differences.If this goes far enough, you can say that macroevolution has occured, because you compare the two groups and say that they are different enough, but were exactly the same before.The macroevolution is the sum of the previous small evolutionary steps that happened.So to sum up the answer for your last paragraph: Sepparation leads to sepparated microevolution which leads to macroevolution.[This message has been edited by Melchior, 03-26-2004]

Crash
That's how I've always understood it to be as well. The small or Micro changes occur until so many have occurred causing a Macro change because of the fact that the species can no longer interbreed with it's initial population. But the paragraph is saying that what happens to Macro include things that CANNOT happen to the Micro ones.Macro is a result of millions of mutations as apposed to Micro being the result of some mutations. In either case mutations are the cause for BOTH. We're just talking a matter of amount. Walk only a mile, walk 1000 miles, we're still just walking except that I've advanced to another city while you're still stuck in the same city. Right? Why does it even matter if a population has been isolated for these Macro occurrences to happen? In other words Why should it matter if you walked from Chicago and I walked from Detroit (we're separated) for me or you to "have the ability" to walk to Las Angeles? Some are saying it's because we were "separated" that I was able to walk to Las Angeles and at the same time saying that the mere fact of me walking so long "separating" myself further is the reason I was able to walk to Las Angeles. But which is it, Me "being" separated by moving to Detroit or the fact that I've walked so far which makes me separate? In essence is it me being isolated that will get me to Las Angeles or the continual micro changes causing me to get to Las Angeles? You can't use both as the reasons.

Macroevolution is not an event, as Quetzal was trying to communicate. Macroevolution is a point reached by numerous microevolutionary steps. To use an analogy, microevolution is the straw on the camels back, and the straw that breaks the camels back is the macroevolutionary event, or speciation event. To use another analogy, there is an obvious difference between day and night. However, it is hard to determine the exact point where day transfers to night. There is an incremental change from light to dark, but the actual transfer of one into the other is ambiguous.To put it frankly, there is only microevolution. Macroevolution is just the accumulation of microevolution.

Ah, I see what you are wondering about.Sepparation isn't needed for macroevolution itself.You can have a single group and still get changes in the genetic code.However, that group won't split into two different species since any changes would be 'spread' out in the whole group.

Now you're asking two separate questions. "What causes drastic change" and "what gives rise to new species" are two different questions with different answers.In your analogy, what separates us is the fact that you walked to Detroit (the drastic change stemming from accumulating mutation) and the fact that I didn't go with you (the reproductive isolation).Us being separated didn't get you to Detroit. Reproductive isolation doesn't cause adaptation, of course. What it does cause is noninterfertility. If the populations hadn't separated - if I had gone with you to Detroit - speciation wouldn't have happened, no matter how drastic the change was. No matter how far you go, if I went with you, we're still in the same place as each other.Does that make it any clearer? It's the changes that get you to Detroit. But it's the fact that you went there alone that makes you a new species.

Melchoir
By George (Melchoir)I think you've got it! "You can have a single group and still get changes in the genetic code.
However, that group won't split into two different species since any changes would be 'spread' out in the whole group. "Now we're talking.And that's the question, WHY won't they split into two different species? Well, we're told because they're still part of the same group. So...we separate them. Now we have 2 separated groups. So that now any changes occurring will be separate. But you see, Houston, we still have a problem. You have just "doubled" the REAL issue. Because even in the second separated group the changes, micro ones, will be spread into THAT group as well, albeit different changes from the initial group. What we REALLY want to know is WHEN or HOW does a Macro result occur in EITHER group? I've always read that it's through many many micro changes a Macro result is achieved. So... HOW could the resulting Macro change include things that CANNOT happen to the "lesser groups" of which micro changes are occurring that eventually lead up to the resulting Macro change? If you say by "seperating" them you've just completed a circular argument.

try this posting by Quetzal:http://EvC Forum: What is your favorite example of speciation? speciation occurs when two varieties of a species become so different from accumulated change that they no longer are capable of interbreeding.and yet each level of change that occurs is your "micro" evolutionary change"macro" = sum (enough "micro")

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist