A question about evolution

Did it? It's not clear that the two groups of birds aren't part of the same population to begin with.If they were, then no, evolution did not occur because allele frequencies didn't change as a result of selection.Really it comes down to what is meant by "original population."

Well, what would you call it if my sister drives down from Minneapolis and nobody gets killed along the way?I mean, did my family just get larger? No, she was part of the family all along, just a geographically distant part of it.We don't know where these additional birds came from. The fact that they're so easily absorbed into the main population in the first place indicates to me that we're not supposed to view them as different species or different populations merging - merely, it's a goofy explanation for why there's homozygous individuals for both traits but no heterozygotes.It was all one population to begin with. Since allele frequencies weren't changed by the storm, no selection happened. So no evolution happened.

No, it doesn't, because the only difference between a human and some pond scum is different genes. Genes make the organism.Hence, any natural feature that can change the contents of genes is sufficient to result in pond scum eventually giving rise to humans, because all it takes is changing genes over time.

How so? It seems to me that the definitions are being supplied by the question.If they can so easily merge then it seems ridiculous to assert that they were ever seperate in an evolutionary sense. They're no more seperate populations, and evolution is no more occuring, than if I take all the brown-eyed people over here for ten minutes and then bring them back to the group. What seperation existed between these two groups was illusory and temporal, not a meaningful period of genetic seperation relevant to an evolutionary question. If they weren't part of the original population, they aren't part of the new one. If it was two seperate populations in the beginning then it doesn't make any sense to treat them as two seperate populations throughout, and in that case, there's still no evolution because the populations haven't been in proximity long enough for any gene flow to occur. Either they're a population throughout, or they're two seperate populations throughout. There's no description of any kind of mating activity and it doesn't make sense to treat two groups of the same species as two populations "merging" into one just because they came within geographic proximity. Still no evolution, because they're not part of the same population now. There's absolutely no indication of any gene flow between members of these two groups in the timeframe of the question. They're apparently different allotypes of the same species in momentary geographical proximity. The fact that they're in proximity to each other is meaningless, evolutionarily speaking.I think your problem is that you're treating the populations as real things, rather than seeing that it's the individual birds who are real, and that you don't suddenly join another individual's species simply because you're standing next to them. You don't suddenly become an African-American just because you moved to Harlem.

"Specie" is money. "Species" is the term for a reproductive community of organisms. It's its own plural. This is not the merging of two populations because calicos and tabbys are part of the same population - Felis sylvestris catus.

How? Just by proximity? That doesn't make any sense. How are they any suddenly part of the same gene pool simply because their members are standing next to each other? To suit our own arbitrary purpose? No, I don't think we can. Species has a definition, gene pool already means something, and I don't think allele frequencies change just because two birds are suddenly flying next to each other. Only if those individuals were part of the gene pool. For that to be the case, gene flow had to be occuring between those individuals and the other individuals in the gene pool.My point is pretty simple - either the new birds were always part of the gene pool, or else they're not a part of it at all. They don't just become part of the pool simply by physical proximity to other individuals. Otherwise you'd be a zebra every time you went to the zoo.

Then we can control evolution with our minds, just by marks on paper.That's incoherent to me. The question is not about what we consider a population, the question asks about whether or not evolution happened, where evolution is a change in allele frequencies as a result of random mutation and natural selection.I don't see any mutation or selection in the example. The storm isn't a selective force in the context of the question (though storms certainly could select certain traits over others.) So we can discount evolution right there. "Melding" populations - that is, us redrawing the lines - isn't a selective force either.There's no change in allele frequencies due to selection here. There may not be a change in frequencies at all - under 2 of the three reasonable interpretations of the situation, there's no reason to consider a shift in allele frequencies. There's simply a shift in our perception. That's not evolution; that's basically a Jedi mind trick.Just because you can imagine a map where south is at the top doesn't change the orientation of the Earth. Just because you can imagine a line that moves to encompass these new individuals doesn't mean that the individuals have, in any objective way, become part of the population. Until they're involved in gene flow with the larger population they're irrelevant to it, except as part of the environment that might be involved in selection (i.e. as competition for food or mates.) Yeah. "Bullshit."No, seriously. I'm not aware of any term for that, and it would be incoherent for there to be one. That's not the evolution of a species; it's just humans changing their mental models. It's no more significant to the physical reality of the species than it is when species names get changed. It's just humans changing marks on paper, not a reflection of a changing physical reality. By gene flow. A species represents a reproductive community. If these new individuals aren't reproducing with the old ones, they're not a part of the population - any more than you become part of the anthill when you step on it. But you're already involved with gene flow with the people at the zoo. Perhaps some of your distant relatives are there. If your family has long-term ties to the community, that's certainly the case.So the fact that you went to the zoo doesn't change the allele frequencies of any population; you were already a part of the population that is here at the zoo before you came. Evolution doesn't happen simply because you walk into the room and change the "allele frequencies" represented by the population in the room. That simply doesn't make any sense. It doesn't make any sense to draw a boundary there.Similarly, it doesn't make any sense to draw a boundary between the aa individuals who were over here and the bb individuals who were over there, unless that boundary represents a species-defining lack of interfertility. Even if we want to consider these two populations as re-combining proto-incipient subspecies, they don't actually become part of the same population until they start mating and there's gene flow between them. Until then, they're just in physical proximity.Evolution doesn't happen just because birds get close to each other. That doesn't make any sense! Maybe after the storm, the bb individuals go on their merry way, so there never was any gene flow between them. What possible basis would we have then for concluding that they were ever part of the same population, the same species? That we should consider their alleles as a sum rather than in seperate domains? None whatsoever. So why on Earth does it make any sense to try to do that now, well before we have any indication that such an approach would even make sense?Edited by crashfrog, : No reason given.

We don't know that. We don't even know they're the same species. All we know is that two flocks met each other and came into physical proximity right before a storm.That strikes me as a pretty flimsy basis to conclude that there's a sudden introduction of a bunch of new alleles. We have absolutely no indication that any gene flow between the two groups has occured or will occur. If no gene flow ever happens then the bb individuals were never a part of the same gene pool as the aa individuals. That's a great new word that I didn't know. Thank you very much. That's what I've been saying all along, if we assume they're the same species (as the question implies but does not state.) Sure. But the introduction of new alleles doesn't happen until mating season. Until then we're looking at two seperate demes, physically superimposed. No more significant than walking into a room. If they do mate, we might retroactively describe the migration event as the instant when the two populations became one.But if they don't ever mate, then it doesn't make any sense to refer to the migration event as the joining of anything. Does that make sense?

Sure. But when something comes in from "out of the frame", as it were, that should not confuse us into thinking that evolution is happening just because somebody walked into the room. If they're not part of the same reproductive community, then by definition, it's two different species.I don't mean to imply that it's always cut-and-dry whether or not two individuals are in the same reproductive community. How this is tested, practically, is a large area of debate among biologists. Because that could be what's going on here. This could be two seperate species.You're not an ant, yes. You'll never be in the ant species. The reason for this is not because you lack the "ant essence", it's because you'll never be part of a reproductive community of ants.You don't, obviously, join the community just because you're near an anthill. You don't join any other communities just by physical proximity either. You have to be part of the reproductive community. That is to say, mating with members of that community. Until you're mating in it, your claim to be part of it is tenuous. We might give you a bogey on it in a practical situation. As a human being we might assume you're going to be mating with humans sometime in the future.It's not stipulated that these are the same species. It's not stipulated that they aren't but I find that a tenuous basis to go off assuming a massive introduction of new alleles into a population. They're called "airplanes." There's nowhere in the world you can go where you aren't part of that reproductive community. I don't see that there are any evolutionarily-relevant populations that don't include you in an age of easy intercontinental travel. And I think that would be pedantic and dumb. If I lost points on such a question because I wasn't willing to be pedantic, I'd certainly argue it with the prof. (During office hours.) Welcome to biology, I guess. Things are fuzzy. Species boundaries cannot be rigidly drawn. In a real sense, there may not even be species or reproductive communities. In a sense, there is just the individual and the environment, and they interact.I think it can be argued either way and I think you've done a great job advancing your position. I think there's basically no wrong answer to this question because it's framed so poorly. I'd like to know what the person who wrote it thought the right answer was.

Well, I agree with you. But I'm sure you know what the problem is. The universe is continuous; our words are discreet. For instance we might say "hot" and "cold" are temperatures, but actual temperatures can be anywhere in between hot and cold. So we get more precise - we say "degrees Celsius." But you can have a temperature between 91 and 92 degrees. So we say we can have decimal degrees. But between any two points on the thermometer, you can have an intermediate temperature.We apply discreet labels, like "species" or "evolution", to phenomena in the universe that vary continuously and in infinite directions. It's no surprise at all that we should find phenomena that meet dictionary definitions of our words, but that we intuit aren't actually examples of what we were trying to describe in the first place. Well... it depends on what you mean by "reproductive community."Sorry. That wasn't made explicit in the OP, but it has been since, so I'll consider it stipulated that all these birds are conspecifics. I agree. Part of the problem is that the creation/evolution debate is always kind of in the background, biology instructors know that a fair number of their students are sitting there looking for an opening that looks like a failing of biology or any kind of hand-waving, and so they portray a certainty or a rigidity that isn't really supported by the facts. Another part of the problem is that no expert wants to look like there's something major he doesn't know. How much respect could biology unjustly lose because it looks like we all have our heads up our asses and we don't even know what a species is?I mean, everybody thinks they know what a species is, if you ask them, they'll even give examples. "Squirrels." "Dogs". etc. To the layperson, "species" simply means "all the organisms of the same type." But the dirty little secret (and the reason creationism is wrong) is that organisms aren't typed. They don't come with serial numbers that tell you what species they're an individual of. It's not stamped on their fur or under a leaf. It's not even encoded in their genetics.We just have to guess what species they are, based on what other organisms they're similar to. "Similar" could mean many things - similar in shape, color, or other physical characters, or similar in terms of their genetics. Similar in form gets tricky when you realize that individuals vary in form. Males are different than females, but in the same species. (Of course, what's a "male"? What's a "female"? Sometimes that means different things for different organisms.)There's an exception to every rule, and exceptions to the exceptions. Things in the natural world mostly make sense, but there's no framework you can develop where an organism hasn't evolved that doesn't fit neatly inside it.But it wouldn't be any fun, otherwise!Edited by crashfrog, : No reason given.Edited by crashfrog, : No reason given.