Macroevolution Observed?

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.

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

I think loudmouth may have already covered this, but I wanted to clarify my response. I guess I didn't articulate it well. You say, If you'll look back at the post to which you responded, you'll see that I DID indicate what that "something" was: reproductive isolation that arises between two populations (or within one population occasionally). I used "something" to generically describe the various isolating mechanisms I listed:

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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.

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The way I used the term wasn't intended to indicate ambiguity - it was a catchall reference to the mechanisms I listed. The point being that the specific mechanism is unimportant to this particular discussion, once such mechanisms are active, divergence occurs.IOW, the "something" isn't macroevolution - which is a term used for a result, not a mechanism. The "something" IS the mechanism - one or another (or sometimes multiple) isolating mechanism. Why not? Let me try to simplify a rather complex process (to all pop geneticists: please don't send me hate mail ). In the first place, evolution doesn’t proceed by sudden leaps — saltation or instantaneous macroevolution — in major morphology. The basic reason is that the larger the effect of a given mutation, for example, the more likely it will be deleterious — and kill the mutant. In addition, the "hopeful monster" scenario (where a "freak" appears in a population that has no mate, for instance) has been effectively falsified. That’s not to say small mutations can’t have a deleterious effect on the organism, just that large ones would be almost invariably fatal. What normally happens is that a small mutation occurs in a population, and over several generations is passed down to the offspring of the original mutant. This MAY split the population into two different varieties (for the sake of this discussion, let's assume that's what happened). Now if these two varieties lived close by one another, the odds are that they would interbreed, and the mutation would be suppressed or eliminated over time. Allele frequency tends to be pretty hard to budge once fixed in a population. However, what do you think would happen if a portion of the population carrying the mutation were to become geographically (or behaviorally, or temporally or "something" ) isolated from the parent population? The mutation, if it provides a net survival advantage in the new area, will rapidly become fixed in the new population. In addition, both populations continue to change due to environmental conditions, or even chance (genetic recombination, additional mutations, etc leading to changes in allelic frequency in both populations). If the two populations are reunited eventually, and they don’t interbreed, then we can say they are in fact two distinct species. The longer they are apart, the more differences we would expect. Natural selection operates on both populations - but the selection pressures (and hence adaptive landscape) is going to be different for both. Over time, selection can even "co-opt" genes, combinations of genes, or even macrostructures that are useful for one thing in the parent population to another function in the new one based on the adaptive landscape. Voila: macroevolution.