A question about evolution

They were reproductively isolated from one another. Let us say some short range migratory birds are blown off course. Most of them die, and the survivors are forced to ground on a remote volcanic island.No other members of their species arrive and it stays that way for 10,000 years. This population of geographically isolated birds has 100% frequency of a certain allele - and they are effectively reprodctively isolated since they can't physically get to the other birds without a storm to blow them that way (and vice versa)After 10,000 years another ragtag group of birds gets to the island. They alter the allele frequencies. The question in the OP throws in a bit of selection too. This new allele seems a bit better at weathering certain types of storm. Yes - and demes have their own definition - geographically isolated populations. This island population has next to zero gene flow with the mainland variety. They are following their own evolutionary path, with a very rare (or even unique) allele making it in from elsewhere. It is likely they will eventually drift to the point of speciation (much like Darwin's finches).The question then is: has evolution occurred if the allele frequencies of a deme change, but the allele frequencies of the entire potential reproductive community hasn't?I say it is evolution, because one of the driving factors behind evolution is reduction in gene flow from sections of a population which allows the sections of the species to evolve in different directions leading to diversity. They were all part of a potential gene pool (much like lions and tigers are part of a potential gene pool), however there is some isolation between them (due to geography) which hinders gene flow. They can produce viable offspring if/when they come in contact.As can the birds, they are isolated but could reproduce if only there wasn't some barrier between them (unlike humans and zebras (though I've never personally tested this)). Migration into otherwise isolated populations is defintely part of evolution - and is one of the wonders of sexual recombination.Demes can evolve. I contend that demes can evolve due to sexual migrants inserting an occasional new allele (or just increasing the frequency of certain alleles) thus increasing the deme's diversity.

Heh - if we want to be over literal about it. It would render the structure of the question unnecessary. We could just say: Some guy walks into a room full of dogs, is this evolution? To even ask the question is absurd. No probs, I don't use it often enough - but I like it nevertheless. Perhaps. However, I think that would be perhaps looking at the question too literally. When the animals migrated into a population, it is implied by the word population that they formed a reproductive community.Unless the new birds were too old to reproduce (have already been effectively selected out), then evolution is taking place. Some new alleles are now present in the deme's pool which are subject to selection. The new birds may never get to mate (their allele might be strongly selected against in the environment), but it would still be evolution.Since the answer to the question is 'Yes', we can safely make the assumptions that they meant this. Without the context we'd have to list our assumptions. It certainly does make sense, I just don't completely agree. It's a minor technical point, of course, but what else can otherwise like minded people find to disagree on?

A bit out of the blue for this thread But yes, they are excellent material. Long long long, but filled with an interesting and wonderful exchange of ideas.

http://beyondbelief2006.org/Watch/