What prevents evolution?

[Matt R.]

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.

[Rduke55]

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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.

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Nice!

[Skidoo]

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The mutual infertility of the individuals within group B increases according to the same genetic drift that underlies the development of mutually fertile group A into (prospectively) mutually fertile group B.

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Infertility with respect to whom?

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Each other.

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Each other at the individual level?

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Yes.

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Are you being vague on purpose?

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No.

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Then who do they mate with?

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That's just my point.

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How many generations would you say this infertility takes to get to?

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About the same number of generations separating the mutual fertility of group A and group B.

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So you have a group of individuals where none of them can mate with each other?

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Unfortunately.

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And in the 2nd response, where do you get that idea from?

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To coin a phrase (with apologies): what would stop it from happening?

[Skidoo]

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Selection, like something else I won't mention, happens.

It's the notion of speciation that's got issues with logic.

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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?

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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.

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A larger point is that speciation, defined as the production of a new group with which the original is not mutually fertile, is essential to the supposed process of evolution.

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but you've been preaching on the development of infertility the whole thread.

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Let's not get carried away with metaphors.

[Rduke55]

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So you have a group of individuals where none of them can mate with each other?

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Unfortunately.

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Each individual? How the hell does that happen?

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And in the 2nd response, where do you get that idea from?

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To coin a phrase (with apologies): what would stop it from happening?

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I was asking how do you know how many generations it takes but if you're talking about individuals within a population being infertile with each other then we've got some educating to do.

I'm interested how you put these snippets together into a point of view.

The whole thread you've been talking about speciation yet saying it doesn't happen.

I'm off to bed.

[vhawk01]

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Selection, like something else I won't mention, happens.

It's the notion of speciation that's got issues with logic.

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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?

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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.

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That's what species are - reproductively isolated populations. they can interbreed with each thter and are infertile with other species.

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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.

[vhawk01]

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Selection, like something else I won't mention, happens.

It's the notion of speciation that's got issues with logic.

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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?

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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.

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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.

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Are you saying its sufficient as well as necessary?

[Magic_Man]

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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.

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That certainly makes sense. Obviously if gene flow is disrupted, speciation follows. But can't it within a group by some mechanism I've described? Say a mutation creates a recessive gene in an individual, and has no other noticeable effects. That individual will most likely produce some offspring, so we'll have a few individuals running around with this recessive gene. On the offchance that two of them mate, the gene will manifest itself. Perhaps it makes them fertile only with the carriers, with some difficulty. Their pairings will give us more offspring that have the trait, and that new generation will be more likely to mate with each other than with the carriers...and so it goes. Can speciation happen this way?

~MagicMan

[Skidoo]

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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.

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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.

[Rduke55]

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Selection, like something else I won't mention, happens.

It's the notion of speciation that's got issues with logic.

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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?

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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.

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That's what species are - reproductively isolated populations. they can interbreed with each thter and are infertile with other species.

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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.

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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.