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#131
12-08-2006, 02:03 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] Magic_Man, I don't like the "mutated" vs. "not-mutated" disctinction. I think it's quite a bit harder to understand speciation if you think of it in this context. Think of a group that is comprised of individuals who are mutually fertile with one another. A very high percentage of this population can successfully mate with another individual of the opposite sex within this population. Not EVERY individual can, which I think is an important note. Some event occurs which splits this population in two. Say it's a physical barrier... It doesn't necessarily *have* to be physical, but it must be something that prevents gene flow. Now, population 1 continues to change over time due to mutation/selection. Population 2 does as well. But, because they are not exchanging genes, they are no longer "co-evolving" sexually (to use the term loosely). The longer they remain out of contact (in terms of number of generations) the less likely it is that the future generations can mate successfully with the opposite population. There is no selection for fertility BETWEEN the populations -- thus the random mutations introduced will tend to cause them to diverge. At some point, it becomes very difficult for members of population A to mate with population B. Then, voila, we have two new species in terms of the classical definition. Over time, because they do not experience gene flow, there will tend to be massive differences in morphology which is why species tend to "look" so different. [/ QUOTE ] Matt: A simple working definition is called for. If two individuals are potentially fertile with each other, they are of the same species. If not, they aren't. [/ QUOTE ] Now you're getting it! 
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#132
12-08-2006, 02:04 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] Magic_Man, I don't like the "mutated" vs. "not-mutated" disctinction. I think it's quite a bit harder to understand speciation if you think of it in this context. Think of a group that is comprised of individuals who are mutually fertile with one another. A very high percentage of this population can successfully mate with another individual of the opposite sex within this population. Not EVERY individual can, which I think is an important note. Some event occurs which splits this population in two. Say it's a physical barrier... It doesn't necessarily *have* to be physical, but it must be something that prevents gene flow. Now, population 1 continues to change over time due to mutation/selection. Population 2 does as well. But, because they are not exchanging genes, they are no longer "co-evolving" sexually (to use the term loosely). The longer they remain out of contact (in terms of number of generations) the less likely it is that the future generations can mate successfully with the opposite population. There is no selection for fertility BETWEEN the populations -- thus the random mutations introduced will tend to cause them to diverge. At some point, it becomes very difficult for members of population A to mate with population B. Then, voila, we have two new species in terms of the classical definition. Over time, because they do not experience gene flow, there will tend to be massive differences in morphology which is why species tend to "look" so different. [/ QUOTE ] Matt: A simple working definition is called for. If two individuals are potentially fertile with each other, they are of the same species. If not, they aren't. [/ QUOTE ] How does this apply in the A-->B-->C case? By your definition, A & B are the same species, and B & C are the same species, AND YET! A & C aren't the same species? This happens in the real world. Defining a "species" is a tricky pancake. ~MagicMan
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#133
12-08-2006, 02:06 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] Selection, like something else I won't mention, happens. It's the notion of speciation that's got issues with logic. [/ QUOTE ] But you said populations could become mutually infertile with each other. (That's what speciation is) And what's the something you won't mention? [/ QUOTE ] Actually, I totally agree with him. Speciation really is a logically meaningless distinction. I mean, unless 'species' only means EXACTLY cannot mate with any other species. But even thats iffy, they can mate, with varying success, some of the times. Calling two different things different species is a (nearly completely) arbitrary distinction. If that was Skidoo's point (I doubt it was) then I agree completely. [/ QUOTE ] That's what species are - reproductively isolated populations. they can interbreed with each thter and are infertile with other species. [/ QUOTE ] Hmmm. Its misleading at the very least, and it is pretty arbitrary. It just seems so...contrived. I understand that it IS contrived, and its meant as some sort of 'at the very least THIS different' type of line. But the amount of difference that might cause one particular set of groups, call them A and B, could be one single mutation. And in some other set, A' and B', they could accumulate hundreds of differences and still be able to reproduce if they were only reunited. And then they could be reunited. So they would be different species while they were on different islands, but the same species if we just moved them a few miles. I know those are pretty impractical examples, in that groups with many, many mutations aren't likely to choose to mate with each other, but as long as they fit and as long as not too many of the mutations were to the reproductive machinery, etc... I can buy it. I just don't like it. [/ QUOTE ] Speciation is certainly not a measure of genetic difference. It's what I said before about fertility. In your examples, the first would be different species, the second would not be - even when they are on different islands. [/ QUOTE ] Are you sure about that? I don't think thats correct. I was under the impression that mutual infertility didn't HAVE to be because of a morphological or developmental barrier, but could be because of a behavioral one. Imagine if instead of seperate islands they are on seperate mating season schedules instead. This is theoretically identical to islands, except they see each other and interact but don't mate. They can not mate with each other, because one mates in the Spring wheras the other mates in the Fall, even though they could if they just tried. These count as different species, by my understanding...is that wrong? And then what happens if one group switches back to mating at the same time?
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#134
12-08-2006, 02:06 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] [ QUOTE ] Magic_Man, I don't like the "mutated" vs. "not-mutated" disctinction. I think it's quite a bit harder to understand speciation if you think of it in this context. Think of a group that is comprised of individuals who are mutually fertile with one another. A very high percentage of this population can successfully mate with another individual of the opposite sex within this population. Not EVERY individual can, which I think is an important note. Some event occurs which splits this population in two. Say it's a physical barrier... It doesn't necessarily *have* to be physical, but it must be something that prevents gene flow. Now, population 1 continues to change over time due to mutation/selection. Population 2 does as well. But, because they are not exchanging genes, they are no longer "co-evolving" sexually (to use the term loosely). The longer they remain out of contact (in terms of number of generations) the less likely it is that the future generations can mate successfully with the opposite population. There is no selection for fertility BETWEEN the populations -- thus the random mutations introduced will tend to cause them to diverge. At some point, it becomes very difficult for members of population A to mate with population B. Then, voila, we have two new species in terms of the classical definition. Over time, because they do not experience gene flow, there will tend to be massive differences in morphology which is why species tend to "look" so different. [/ QUOTE ] Matt: A simple working definition is called for. If two individuals are potentially fertile with each other, they are of the same species. If not, they aren't. [/ QUOTE ] How does this apply in the A-->B-->C case? By your definition, A & B are the same species, and B & C are the same species, AND YET! A & C aren't the same species? This happens in the real world. Defining a "species" is a tricky pancake. ~MagicMan [/ QUOTE ] Most of the time it isn't. Now I'm definitely going to bed. Thanks for keeping me up, jerks. [img]/images/graemlins/grin.gif[/img]
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#135
12-08-2006, 02:07 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] [ QUOTE ] Magic_Man, I don't like the "mutated" vs. "not-mutated" disctinction. I think it's quite a bit harder to understand speciation if you think of it in this context. Think of a group that is comprised of individuals who are mutually fertile with one another. A very high percentage of this population can successfully mate with another individual of the opposite sex within this population. Not EVERY individual can, which I think is an important note. Some event occurs which splits this population in two. Say it's a physical barrier... It doesn't necessarily *have* to be physical, but it must be something that prevents gene flow. Now, population 1 continues to change over time due to mutation/selection. Population 2 does as well. But, because they are not exchanging genes, they are no longer "co-evolving" sexually (to use the term loosely). The longer they remain out of contact (in terms of number of generations) the less likely it is that the future generations can mate successfully with the opposite population. There is no selection for fertility BETWEEN the populations -- thus the random mutations introduced will tend to cause them to diverge. At some point, it becomes very difficult for members of population A to mate with population B. Then, voila, we have two new species in terms of the classical definition. Over time, because they do not experience gene flow, there will tend to be massive differences in morphology which is why species tend to "look" so different. [/ QUOTE ] Matt: A simple working definition is called for. If two individuals are potentially fertile with each other, they are of the same species. If not, they aren't. [/ QUOTE ] How does this apply in the A-->B-->C case? By your definition, A & B are the same species, and B & C are the same species, AND YET! A & C aren't the same species? This happens in the real world. Defining a "species" is a tricky pancake. ~MagicMan [/ QUOTE ] Yes, the ring species are a MUCH better example of my beef with the whole concept of speciation, I really should have just gone with this from the beginning. Then Rduke would have agreed with me from the start and I could have saved myself the embarassment.
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#136
12-08-2006, 02:08 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] Magic_Man, I don't like the "mutated" vs. "not-mutated" disctinction. I think it's quite a bit harder to understand speciation if you think of it in this context. Think of a group that is comprised of individuals who are mutually fertile with one another. A very high percentage of this population can successfully mate with another individual of the opposite sex within this population. Not EVERY individual can, which I think is an important note. Some event occurs which splits this population in two. Say it's a physical barrier... It doesn't necessarily *have* to be physical, but it must be something that prevents gene flow. Now, population 1 continues to change over time due to mutation/selection. Population 2 does as well. But, because they are not exchanging genes, they are no longer "co-evolving" sexually (to use the term loosely). The longer they remain out of contact (in terms of number of generations) the less likely it is that the future generations can mate successfully with the opposite population. There is no selection for fertility BETWEEN the populations -- thus the random mutations introduced will tend to cause them to diverge. At some point, it becomes very difficult for members of population A to mate with population B. Then, voila, we have two new species in terms of the classical definition. Over time, because they do not experience gene flow, there will tend to be massive differences in morphology which is why species tend to "look" so different. [/ QUOTE ] Matt: A simple working definition is called for. If two individuals are potentially fertile with each other, they are of the same species. If not, they aren't. [/ QUOTE ] How does this apply in the A-->B-->C case? By your definition, A & B are the same species, and B & C are the same species, AND YET! A & C aren't the same species? This happens in the real world. Defining a "species" is a tricky pancake. ~MagicMan [/ QUOTE ] Most of the time it isn't. Now I'm definitely going to bed. Thanks for keeping me up, jerks. [img]/images/graemlins/grin.gif[/img] [/ QUOTE ] Damn, I was actually hoping to get a response to my last post before I too go to bed.
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#137
12-08-2006, 02:10 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] Selection, like something else I won't mention, happens. It's the notion of speciation that's got issues with logic. [/ QUOTE ] But you said populations could become mutually infertile with each other. (That's what speciation is) And what's the something you won't mention? [/ QUOTE ] Actually, I totally agree with him. Speciation really is a logically meaningless distinction. I mean, unless 'species' only means EXACTLY cannot mate with any other species. But even thats iffy, they can mate, with varying success, some of the times. Calling two different things different species is a (nearly completely) arbitrary distinction. If that was Skidoo's point (I doubt it was) then I agree completely. [/ QUOTE ] A larger point is that speciation, defined as the production of a new group with which the original is not fertile, is essential to the supposed process of evolution. [/ QUOTE ] Are you saying its sufficient as well as necessary? [/ QUOTE ] It's at least necessary. I'm not so sure about sufficient.
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#138
12-08-2006, 02:10 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] Selection, like something else I won't mention, happens. It's the notion of speciation that's got issues with logic. [/ QUOTE ] But you said populations could become mutually infertile with each other. (That's what speciation is) And what's the something you won't mention? [/ QUOTE ] Actually, I totally agree with him. Speciation really is a logically meaningless distinction. I mean, unless 'species' only means EXACTLY cannot mate with any other species. But even thats iffy, they can mate, with varying success, some of the times. Calling two different things different species is a (nearly completely) arbitrary distinction. If that was Skidoo's point (I doubt it was) then I agree completely. [/ QUOTE ] That's what species are - reproductively isolated populations. they can interbreed with each thter and are infertile with other species. [/ QUOTE ] Hmmm. Its misleading at the very least, and it is pretty arbitrary. It just seems so...contrived. I understand that it IS contrived, and its meant as some sort of 'at the very least THIS different' type of line. But the amount of difference that might cause one particular set of groups, call them A and B, could be one single mutation. And in some other set, A' and B', they could accumulate hundreds of differences and still be able to reproduce if they were only reunited. And then they could be reunited. So they would be different species while they were on different islands, but the same species if we just moved them a few miles. I know those are pretty impractical examples, in that groups with many, many mutations aren't likely to choose to mate with each other, but as long as they fit and as long as not too many of the mutations were to the reproductive machinery, etc... I can buy it. I just don't like it. [/ QUOTE ] Speciation is certainly not a measure of genetic difference. It's what I said before about fertility. In your examples, the first would be different species, the second would not be - even when they are on different islands. [/ QUOTE ] Are you sure about that? I don't think thats correct. I was under the impression that mutual infertility didn't HAVE to be because of a morphological or developmental barrier, but could be because of a behavioral one. Imagine if instead of seperate islands they are on seperate mating season schedules instead. This is theoretically identical to islands, except they see each other and interact but don't mate. They can not mate with each other, because one mates in the Spring wheras the other mates in the Fall, even though they could if they just tried. These count as different species, by my understanding...is that wrong? And then what happens if one group switches back to mating at the same time? [/ QUOTE ] That's where the other definitions come in. Try the "cannot produce fertile offspring" idea.
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#139
12-08-2006, 02:11 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] Selection, like something else I won't mention, happens. It's the notion of speciation that's got issues with logic. [/ QUOTE ] But you said populations could become mutually infertile with each other. (That's what speciation is) And what's the something you won't mention? [/ QUOTE ] Actually, I totally agree with him. Speciation really is a logically meaningless distinction. I mean, unless 'species' only means EXACTLY cannot mate with any other species. But even thats iffy, they can mate, with varying success, some of the times. Calling two different things different species is a (nearly completely) arbitrary distinction. If that was Skidoo's point (I doubt it was) then I agree completely. [/ QUOTE ] That's what species are - reproductively isolated populations. they can interbreed with each thter and are infertile with other species. [/ QUOTE ] Hmmm. Its misleading at the very least, and it is pretty arbitrary. It just seems so...contrived. I understand that it IS contrived, and its meant as some sort of 'at the very least THIS different' type of line. But the amount of difference that might cause one particular set of groups, call them A and B, could be one single mutation. And in some other set, A' and B', they could accumulate hundreds of differences and still be able to reproduce if they were only reunited. And then they could be reunited. So they would be different species while they were on different islands, but the same species if we just moved them a few miles. I know those are pretty impractical examples, in that groups with many, many mutations aren't likely to choose to mate with each other, but as long as they fit and as long as not too many of the mutations were to the reproductive machinery, etc... I can buy it. I just don't like it. [/ QUOTE ] Speciation is certainly not a measure of genetic difference. It's what I said before about fertility. In your examples, the first would be different species, the second would not be - even when they are on different islands. [/ QUOTE ] Are you sure about that? I don't think thats correct. I was under the impression that mutual infertility didn't HAVE to be because of a morphological or developmental barrier, but could be because of a behavioral one. Imagine if instead of seperate islands they are on seperate mating season schedules instead. This is theoretically identical to islands, except they see each other and interact but don't mate. They can not mate with each other, because one mates in the Spring wheras the other mates in the Fall, even though they could if they just tried. These count as different species, by my understanding...is that wrong? And then what happens if one group switches back to mating at the same time? [/ QUOTE ] That's where the other definitions come in. Try the "cannot produce fertile offspring" definition. [/ QUOTE ] Ok. Cannot under any circumstances? Like even if we harvest gametes, etc? Because I have a suspicion if we narrow it that far, someone is gonna have to rewrite some textbooks.
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#140
12-08-2006, 02:14 AM
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Re: What prevents evolution?
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] Selection, like something else I won't mention, happens. It's the notion of speciation that's got issues with logic. [/ QUOTE ] But you said populations could become mutually infertile with each other. (That's what speciation is) And what's the something you won't mention? [/ QUOTE ] Actually, I totally agree with him. Speciation really is a logically meaningless distinction. I mean, unless 'species' only means EXACTLY cannot mate with any other species. But even thats iffy, they can mate, with varying success, some of the times. Calling two different things different species is a (nearly completely) arbitrary distinction. If that was Skidoo's point (I doubt it was) then I agree completely. [/ QUOTE ] That's what species are - reproductively isolated populations. they can interbreed with each thter and are infertile with other species. [/ QUOTE ] Hmmm. Its misleading at the very least, and it is pretty arbitrary. It just seems so...contrived. I understand that it IS contrived, and its meant as some sort of 'at the very least THIS different' type of line. But the amount of difference that might cause one particular set of groups, call them A and B, could be one single mutation. And in some other set, A' and B', they could accumulate hundreds of differences and still be able to reproduce if they were only reunited. And then they could be reunited. So they would be different species while they were on different islands, but the same species if we just moved them a few miles. I know those are pretty impractical examples, in that groups with many, many mutations aren't likely to choose to mate with each other, but as long as they fit and as long as not too many of the mutations were to the reproductive machinery, etc... I can buy it. I just don't like it. [/ QUOTE ] Speciation is certainly not a measure of genetic difference. It's what I said before about fertility. In your examples, the first would be different species, the second would not be - even when they are on different islands. [/ QUOTE ] Are you sure about that? I don't think thats correct. I was under the impression that mutual infertility didn't HAVE to be because of a morphological or developmental barrier, but could be because of a behavioral one. Imagine if instead of seperate islands they are on seperate mating season schedules instead. This is theoretically identical to islands, except they see each other and interact but don't mate. They can not mate with each other, because one mates in the Spring wheras the other mates in the Fall, even though they could if they just tried. These count as different species, by my understanding...is that wrong? And then what happens if one group switches back to mating at the same time? [/ QUOTE ] That's where the other definitions come in. Try the "cannot produce fertile offspring" definition. [/ QUOTE ] Ok. Cannot under any circumstances? Like even if we harvest gametes, etc? Because I have a suspicion if we narrow it that far, someone is gonna have to rewrite some textbooks. [/ QUOTE ] As in if even if we took sperm from this species and an egg from that one and combined them, we would not get fertile offspring. That's one of the most common definitions. I don't see what the issue is with it.
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