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Author | Topic: Does microevolution logically include macroevolution? | |||||||||||||||||||||||||||
robinrohan Inactive Member |
This topic may have already been discussed in the past ad naseum, so if Admin. wants to reject it on the grounds of staleness, I certainly understand.
I don't know a lot about TOE, so the claim I am making is very tentative. With this topic, I am here to be instructed more than to argue. But here's my idea: The system of labelling various life forms by dividing them into different species is merely a classificational scheme and is not meant to set forth the idea of essential characteristics of any given species. It is difficult to pinpoint along some evolutionary line precisely when a new species appears. I suppose in the past classification schemes were based on physical characteristics until somebody decided it made more sense to classify according to isolated gene pools. But even with this scheme, there appear to be some exceptions (dogs/wolves), which shows us that the classification scheme is merely a convenience, though perhaps the one that makes the most sense. So what happens is that the life form continues to change and after a while one group of life forms becomes insolated in terms of breeding from another group. When this isolation occurs, for whatever reason, the two groups continue to evolve separately and after a long time we can notice a difference in physical traits. The distinction between "microevolution" and "macroevolution" sounds fishy to me. Isn't all evolution "microevolution" since the changes are so gradual? It's not like there's some definite line of demarcation that is crossed where what was microevolution suddenly becomes macroevolution, is there? There are just these continuous small changes, caused by imperfect replication and mutation, and influenced by the environment, and this gradual change has to be continuous. There is no logical reason for the changes to stop within a certain circle of possible changes beyond which the life form cannot change--at least not that I can see. I conclude, therefore, that if you accept microevolution you also have to accept macroevolution. This message has been edited by robinrohan, 06-13-2005 01:38 PM This message has been edited by robinrohan, 06-13-2005 01:40 PM This message has been edited by robinrohan, 06-13-2005 01:44 PM This message has been edited by robinrohan, 06-14-2005 04:44 AM
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Admin Director Posts: 13042 From: EvC Forum Joined: Member Rating: 2.3 |
Thread moved here from the Proposed New Topics forum.
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.3 |
I can't see any inherent contradiction in the view that organisms exist in what are, essentially, viable islands in the sea of possible genomes. So that a cat, for example, could evolve to be bigger, smaller, more aggressive or blacker but not evolve into an aquatic mammal akin to a seal because there exists no gradual pathway between the two possible organisms.
Of course the evidence contradicts this view; but I can't see any logical reason it couldn't be that way.
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PaulK Member Posts: 17828 Joined: Member Rating: 2.3 |
It is worth noting that the distinction between macroevolution and microevolution varies depend on who you are talking to,
Biologists usually define macroevolution as evolutionary change at the species or higher taxonomic levels (e.g. speciation and the founding of higher taxonomic groups). Creationists typically define microevolution as "within a kind" but offer no clear way to determine what is a kind or not. Often it is claimed that all individuals with a common ancestor are automatically within the same kind, which would mean that all evolution is "microevolution", no matter how great the change.
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robinrohan Inactive Member |
The whole concept is a little slippery to me. A species is defined as an isolated gene pool. But how did the life form get isolated? If we are talking about geographical isolation, then that in itself hardly seems enough to call it a separate species.
Which comes first, the isolation of the gene pool or the physical changes?
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robinrohan Inactive Member |
Of course the evidence contradicts this view; but I can't see any logical reason it couldn't be that way. The evidence contradicts what view?
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PaulK Member Posts: 17828 Joined: Member Rating: 2.3 |
Species isn't that simple at all there are a number of species concepts in use - and for good reason (we can't apply ideas based on interbreeding to species which do not sexually reproduce or to fossil species for instance). I do know of one case of two recognised species which DO interbreed now that they have come into contact - but their appearance is distinct enough that that is also a factor. I am not aware of any case where geographical isolation alone is considered sufficient.
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.3 |
The view that the existing lifeforms exist in seperated pools of viability with the posible genomes. I.e. that there is no possible pass path between an animal and a very different sort of animal (clearly we're not talking about a cat evolving into a seal, 'cos that isn't what evolution proposses, but that a cat could evolve into something like a seal).
The evidence overwhelming supports a strong evolutionary position that all life on earth evolved from a tiny number of common ancestors (probably, but not yet certainly, one) and, in particular, that all birds, mammals, reptiles and amphibians share a common ancestor.
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robinrohan Inactive Member |
The evidence overwhelming supports a strong evolutionary position that all life on earth evolved from a tiny number of common ancestors (probably, but not yet certainly, one) and, in particular, that all birds, mammals, reptiles and amphibians share a common ancestor. So given enough time, anything can evolve into anything, I guess. But would you say that microevolution automatically leads to macroevolution--unless, of course, a life form dies out?
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Hrun Inactive Member |
I really would suggest that somebody define first what macro-evolution is. I'm certain that this debate will otherwise succumb to the same problem as similar discussions: you can't properly debate a topic when the main concepts ar not properly defined.
That is: if different people understand different things under the term macro-evolution, then the debate becomes meaningless.
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.3 |
So given enough time, anything can evolve into anything, I guess. Depends on what you mean by that. Given time anything can evolve to fit pretty much any niche (assuming the right conditions/competition/etc.) but an aquatic filter feeder evolved from a penguin is not going to be a whale.
But would you say that microevolution automatically leads to macroevolution--unless, of course, a life form dies out? I dislike the terms micro and macro evolution they're too sloppily defined. But yes, I'd say it does. But that's not the same thing as saying it must; which is why proving the occurance of microevolution is not enough to demonstrate the whole theory of evolution.
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robinrohan Inactive Member |
but an aquatic filter feeder evolved from a penguin is not going to be a whale. I see what you're saying, I think. Given a simple life form, the possibilities for change are much greater than if we "start off" with a complicated life form, which already has restrictions built in.
But yes, I'd say it does. But that's not the same thing as saying it must I was thinking that, in a logical sense, it must because it is bound to change--that is if we assume imperfect replication.
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EZscience Member (Idle past 5183 days) Posts: 961 From: A wheatfield in Kansas Joined: |
RR writes: A species is defined as an isolated gene pool. But how did the life form get isolated? If we are talking about geographical isolation, then that in itself hardly seems enough to call it a separate species. There are various ways in which reproductive isolation can be brought about. One is geographic isolation - this leads to allopatric speciation. Over time, geographic isolation means species become more and more different, due partly to differences in selection and partly to random drift. This was touted by Mayr to be the primary and most important way species form, but that view is probably outdated now. Another way you get speciation is parapatric speciation. Here there exist contiguous, adjoining populations that experience different selective forces in their different regions, so that different genotypes are advantageous in each. At some point, both populations benefit by avoiding mating with individuals from the other, so behavioral mechanisms evolve to prevent it and favor those individuals that adopt them. Think different courtship rituals. Finally, there is sympatric speciation where the process occurs within a contiguous population. The 'host-plant fidelity' model in herbivorous insects is an example here. Some individuals start feeding on a new plant species and leave viable offspring. Once they orient to this new plant to find mates, they no longer cross-breed with the parental population and embark on their own evolutionary trajectory. The term 'macroevolution' is typically used by evolutionary biologists to refer to cladistics and phylogenetics - the construction of trees to explain relationships between species and genera within higher order taxa. Since these higher order taxa are not objectively defined like 'species', the term 'clade' is often used to refer to a particular group of genera/species that are monophyletic (can be shown to share a single common ancestor). The combination of modern molecular techniques with conventional morphologically-based taxonomy has recently produced some really powerful inferences in cladistics. This is because the two independent approaches frequently converge on a very similar 'tree', as for example here. If you compare the Figures 1 through 4 you will see that entirely different 'branching rules' nevertheless converge on a very similar tree, the composite hypothesized in Figure 5. This is a macroevolutionary analysis.
RR writes: Which comes first, the isolation of the gene pool or the physical changes? The reproductive isolation (whether accomplished geographically, behaviorally or ecologically) would logically come first. However, this applies specifically to amphimicitic (sexually outcrossing) species. For species with asexual reproduction there is no need for any specific isolating mechanism - all clones diverge independently and there is no real 'gene pool' at all unless sexual forms produced (as they often are on a seasonal basis, for example in aphids).
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EZscience Member (Idle past 5183 days) Posts: 961 From: A wheatfield in Kansas Joined: |
RR writes: So given enough time, anything can evolve into anything, I guess. Not necessarily. The more complicated the organism and the more specialized its ecological niche, the more 'constraints' will limit its evolutionary possibilities.
RR writes: But would you say that microevolution automatically leads to macroevolution--unless, of course, a life form dies out? Bascially, yes. The distinction between the two is merely one of convenience as we try and look back in time to decifer the divergence of higher taxa. All macroevolution begins with microevolutionary changes within populations, but not all microevolutionary changes necessarily lead to macroevolutionary consequences. Good enough? This message has been edited by EZscience, 06-15-2005 11:28 AM This message has been edited by EZscience, 06-15-2005 11:30 AM
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robinrohan Inactive Member |
And you call yourself "EZscience"! But I think I picked up the main drift. If we concentrate on sexual, not asexual species, isolation occurs before physical changes, and there are various ways a life form can be isolated (geographical, behavioral, or change in physical environment, like a new food). After a period of time in isolation, we can label this group a "new species."
All macroevolution begins with microevolutionary changes within populations, but not all microevolutionary changes necessarily lead to macroevolutionary consequences. Good enough? Why would not all microevolutionary changes necessarily lead to macroevolutionary consequences, given enough time? What's to stop the process of change?
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