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Author | Topic: Macroevolution Observed? | |||||||||||||||||||
Loudmouth Inactive Member |
Milagros,
Let's use some real observations here. The following is from Observed Instances of Speciation
In 1964 five or six individuals of the polychaete worm, Nereis acuminata, were collected in Long Beach Harbor, California. These were allowed to grow into a population of thousands of individuals. Four pairs from this population were transferred to the Woods Hole Oceanographic Institute. For over 20 years these worms were used as test organisms in environmental toxicology. From 1986 to 1991 the Long Beach area was searched for populations of the worm. Two populations, P1 and P2, were found. Weinberg, et al. (1992) performed tests on these two populations and the Woods Hole population (WH) for both postmating and premating isolation. To test for postmating isolation, they looked at whether broods from crosses were successfully reared. The results below give the percentage of successful rearings for each group of crosses. WH WH - 75%P1 P1 - 95% P2 P2 - 80% P1 P2 - 77% WH P1 - 0% WH P2 - 0% They also found statistically significant premating isolation between the WH population and the field populations. Finally, the Woods Hole population showed slightly different karyotypes from the field populations.
These two populations of a once interbreeding population were separated for about 30 years. When brought back together, the two populations were not able to produce offspring. The last sentence from the above quote: "Finally, the Woods Hole population showed slightly different karyotypes from the field populations." The karyotype of a genome is the morphological characteristics of the chromosomes. The Woods Hole group shows different chromosome characteristics, and therefore a change in DNA structure. The reason why both populations did not have this change in chromosome morphology is because they were kept separate. Now, did keeping them separate CAUSE the change in the chromosomes? No, this is due to mutation. Did keeping the populations separate cause this change in chromosomes only to happen in one population? YES. Speciation is caused by changes in the DNA AND breeding isolation. If you only have one of these ingredients, speciation will not occur. The changes in the DNA is macroevolution, since such a drastic change is the cause for speciation in isolated populations. However, it was small, incremental steps (microevolution) that led to the overall differences. Therefore, macroevolution is just the accumulation of microevolutionary events. Does this clear things up? (not meant to be sarcastic, BTW. We really want you to understand where we are coming from).
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Corkscrew Inactive Member |
the "evolutionist" version of the pledge of allegiance:
I pledge allegianceTo the flag Of the United States of America And to the republic For which it stands One nation Who used to be tadpoles Indivisible With liberty And justice for all.
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Intruder Inactive Member |
messenjaH of oNe writes: Could macro evolution occur without man's intervention? If so, any naturally occuring ones you know off hand? I believe the terms micro-e and macro-e are terms set by creationists. When you speak of evolution just refer to the "TOE" and the specific mechinism you have a problem with. For example, I believe you are having a problem with mutation, so, maybe you should research mutation. Now in the past I have found that their are no limitations on mutation, and as such, the development of new species/genra would be very likly considering all the evidence we have. p.s. (my opinion) Dont let people with no scientific authority(degree) set limitations with simple terms. I will say they can be very confusing, if you want too check into evolution don't use the goggles provided by creationists. [This message has been edited by Intruder, 03-26-2004] You got intruded. Evolution = chance? = irrelevant.
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
the enlightened version:
I pledge allegiance to the flagOf the United States of America And to the republic for which it stands One nation, indivisible, With liberty, justice and equality for all. we are limited in our ability to understand by our ability to understand RebelAAmerican.Zen[Deist
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
I believe both Gould and Dawkins have used the terms, Gould in his paper on punctuated equilibrium. It does need to be defined to use: currently it is drifting above speciation for most creationists ... Several instances of speciation have been shown, so that would be why.
we are limited in our ability to understand by our ability to understand RebelAAmerican.Zen[Deist
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Intruder Inactive Member |
AbbyLeever writes: currently it is drifting above speciation for most creationists You are right. Macroevolution would be: speciation events and above. I was trying to help "messenjaH of oNe". If he wants to understand Evolution, he needs to use the goggles for lack of a word, that evolutionst wear not the goggles that creationist wear. That was my point. When evolutionst speak together we do not refer too micro and macro, we refer to the "TOE" mechinism, atleast in my experiance. [This message has been edited by Intruder, 03-27-2004] You got intruded. Evolution = chance? = irrelevant.
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
By drifting above I mean that speciation is being moved into micro-evolution and the evidence for it gets too overwhelming ...
Prediction: "macro" will continue to move up the cladistic levels as evidence accumulates so that creationist can continue to say it has not been observed. This is like the definition of "kind" ... if fact they are essentially the same distinction. we are limited in our ability to understand by our ability to understand RebelAAmerican.Zen[Deist
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Intruder Inactive Member |
AbbyLeever writes: By drifting above I mean that speciation is being moved into micro-evolution and the evidence for it gets too overwhelming ... Correct.
AbbyLeever writes:
Prediction: "macro" will continue to move up the cladistic levels as evidence accumulates so that creationist can continue to say it has not been observed. My point exactly, the terms are used by Creationist. I also want to add, why dont creationist stick too the first definition they charted, instead of changing it, or, they could just use the terms accepted, Natural Selection, Mutation, etc.. [This message has been edited by Intruder, 03-27-2004] You got intruded. Evolution = chance? = irrelevant.
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PaulK Member Posts: 17822 Joined: Member Rating: 2.2 |
THis is really quite simple.
We have two populations of a single species which are geographically seperated so that they cannot interbreed. I say that these groups will tend to diverge and that there is nothing to stop a divergence that will lead to an inability to interbreed even if they were brought together again. Ring species are evidence that this is indeed possible. So microevolution can accumulate to the level of macroevolution,
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Quetzal Member (Idle past 5872 days) Posts: 3228 Joined: |
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,
That's exactly what I am trying to get at. That "SOMETHING". 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: quote: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.
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)? 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.
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