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Author | Topic: A question about evolution | |||||||||||||||||||
RAZD Member (Idle past 1432 days) Posts: 20714 From: the other end of the sidewalk Joined: |
... What abut the merging of two populations? <-- questions
A sub-specie. Think of what you would produce if you crossed a Calico and a Tabby. Would you get a new specie? No. Seeing as you are starting within one species to begin with why do you think interbreeding would necessarily produce new species? That is not what the theory of evolution says. It is only when the two sub-species mix and then fail to interbreed that speciation has occurred. Enjoy. we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist
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RAZD Member (Idle past 1432 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Answer: Yes. "Before migration the frequency of allele a was 100%, after migration it was 90%, therefore evolution happened. The storm was not an evolutionary process and therefore did not change the allele frequency." The storm is a straw man in the question as posed. Break it down into three parts (1) Before migration, population is 100% aa, (2) After migration and before storm, population is 90% aa and 10% bb, (3) After migration AND after storm, population is 90% aa and 10% bb. The migration did change the frequency of alleles -- IN the specific population in question. However both populations existed before: thus in a larger context evolution did NOT occur. The population can only be said to change if there were no continued communication between populations in the specific area and other surrounding ones. The storm did not change the frequency of alleles in the specific population in question.If there had been a change then natural selection in favor of one allele over the other would have occurred - and then it would qualify as well.
I don't understand how the mere movement of different alleles is an evolutionary process. In the larger context it isn't. Only when movement is generally prevented or restricted can it influence specific populations. This is where population dynamics come into play - when populations choose not to intermix due to a number of factors. I agree with Crash that the "original population" must be a species definition population for the question to make any sense, in which case no evolution occurred, there was just a movement within the total population of where the aa and bb alleles occurred, not a change in proportions. If we are talking about a variety population then the answer is still no, because there was no change within the aa variety population or the bb variety population, other than loss in numbers due to the storm - there was no interbreeding within the context of the question. I'd be interested in what your professor says to these criticisms. Enjoy. we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist
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RAZD Member (Idle past 1432 days) Posts: 20714 From: the other end of the sidewalk Joined: |
... That would indicate that they cannot even change on the species level. Aside from which, evidence of beneficial mutations are so rare, and have yielded almost nothing in the realm of evidence,... Speciation has been observed, so obviously changes can occur on the species level. Whether they are rare or not is immaterial as long as they exist, as natural selection will filter the results. Natural selection is the driving element of change, mutation just provides the resources for natural selection to act on. we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist
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RAZD Member (Idle past 1432 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Why does you example talk of two different species when exemplifying two populations of the same species? I can never become a part of the ant population but it is possible for the new individuals to flow genes with the old ones. I'm reading a book, an old book - "The Forest and The Sea" by Marston Bates (Random House 1960) - and in it he describes his early research into malaria and mosquito's (although the book is more generally about ecology in layman terms). He does this to exemplify the problems with the concept of species (starting on page 133 near the bottom):
quote: Thus there were seven populations with distinct alleles - aa, bb, cc, dd, ee, ff and gg - and their overlapping in areas did not constitute evolution by changing the proportions of alleles in the "original" population. They had already speciated. Enjoy. Edited by RAZD, : typo compare Fiocruz Genome and fight Muscular Dystrophy with Team EvC! (click) we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist ... to learn ... to think ... to live ... to laugh ... to share.
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RAZD Member (Idle past 1432 days) Posts: 20714 From: the other end of the sidewalk Joined: |
2) They must be together for awhile (geographic isolation --> different populations). I have two problems with this: (1) is that, as presented the bb population just got there and had not had time to interbreed -- therefore "for awhile" does not readily apply, they weren't there long enough, and (2) the bb population could just as easily be a migratory variation to a non-migratory aa population -- they could pass through every year on their migratory route, but still never interbreed because they aren't there during breeding season, whether they could "potentially interbreed and give fertile offspring" or not. There are behavior barriers to mating that prevent interbreeding even if it is possible. The best example of this is the "ring species" the asian greenish warbler: Greenish warblers
quote: Each variation breeds with the neighboring one except at the northern overlap in Siberia where the viridanus and plumbeitarsus varieties ignore each other.
quote: Different behavior affecting breeding. The alleles in the area of overlap between viridanus and plumbeitarsus are in different proportions than in the rest of the habitat for each subspecies , but they are not interbreeding so it doesn't matter.
Forget the storm - It was just an obvious diversion for those students who didn't do their homework. Agreed. BUT if one variety had survived more than the other then it would have been natural selection changing the frequency of alleles in the combined population (if we agree that they now make one population, otherwise it is just survival preference for one population over another).
BTW: How would you define a population that "breeds" asexually. A very good question. What makes a sexually breeding population 'special' is the population dynamics of gene flow between individuals within a species. This can act to hold a species in stasis where it is adequately adapted to its habitat to survive, as sexual pressure can tend to direct the population as a whole towards an average. In asexual populations the gene flow is only in one direction, and as each individual organism picks up mutations those will only be passed to their offspring. It very well could be that what we see as single cell "species" are the remains when interconnecting variations have been removed by natural selection. Genetics can measure the DNA and see how closely related populations are, behavioral and ecological studies can show how they have same reactions to chemicals and habitat, but this may only be an artifact of removal of intermediates to other single cell species. Certainly such populations are isolated from other similar ones -- in many cases (but not all). I did a google and found: (1) http://members.aol.com/darwinpage/mayrspecies.htm
quote: He also talks about other definitions of species that are more historical, but which would have been in effect when asexual species were first type cast. (2) Observed Instances of Speciation
quote: That seems fairly reasonable. This would be the same kind of difference that is used in paleontology to seperate fossils into different species over time when there is no way to see if {organism 1 million years ago} can breed with {organism 5 million years ago}. (3) http://www.msu.edu/course/plb/418/speciesconcepts.htm
quote: This is the only one they list for asexual (they also list BSC - biological species concept - and some others) (4) Birky Lab Home
quote: Asexual organisms are also not constrained by the population gene sharing of sexual species so they can have more variation within a population and the only thing holding that in check is survival of those individuals. From these it looks like asexual species are populations of organisms with similar characteristics that have become isolated by natural selection and time. This is more of an "amoeba" in time description that what remains after selection over time is a species... That's the best I've got at this time. Enjoy. we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist
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RAZD Member (Idle past 1432 days) Posts: 20714 From: the other end of the sidewalk Joined: |
I need a specific question to ask. See Message 37 Do the temporarily temporally coincident groups with aa and bb genes really constitute a "population" if
The best example of this last situation is the "ring species" the asian greenish warbler: the two end species do not interbreed even thought they share a habitat and breed with other varieties that complete a ring of breeding.Greenish warblers we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ... to share.
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RAZD Member (Idle past 1432 days) Posts: 20714 From: the other end of the sidewalk Joined: |
where's the link mod?
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