What prevents evolution?

[vhawk01]

You are entirely positive that, for example, a human egg and a chimpanzee sperm could not be competent? And if that IS obvious, it is equally obvious for ALL groups that we currently consider different species? The vast majority of 'cannot breed' is really just 'does not ever breed for various reasons, morphological and behavioral being primary ones.;

[Rduke55]

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You are entirely positive that, for example, a human egg and a chimpanzee sperm could not be competent? And if that IS obvious, it is equally obvious for ALL groups that we currently consider different species? The vast majority of 'cannot breed' is really just 'does not ever breed for various reasons, morphological and behavioral being primary ones.;

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They are not competent.
The overwhelming majority of what we call species are infertile with each other - as in cannot produce fertile offspring.

[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.

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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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That's good because I like pancakes, with coffee in a roadside dinner after hiking down the mountainside rocky white with snow.

There is no A-->B-->C case, or even a truly A-->B case. That's the whole point.

[vhawk01]

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You are entirely positive that, for example, a human egg and a chimpanzee sperm could not be competent? And if that IS obvious, it is equally obvious for ALL groups that we currently consider different species? The vast majority of 'cannot breed' is really just 'does not ever breed for various reasons, morphological and behavioral being primary ones.;

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They are not competent.
The overwhelming majority of what we call species are infertile with each other - as in cannot produce fertile offspring.

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Ok. I'm willing to accept it, thanks for spending the time. Now go to bed!

P.S. I still win the argument though, because of MagicMan's point about ring species! [img]/images/graemlins/tongue.gif[/img]

[Rduke55]

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You are entirely positive that, for example, a human egg and a chimpanzee sperm could not be competent? And if that IS obvious, it is equally obvious for ALL groups that we currently consider different species? The vast majority of 'cannot breed' is really just 'does not ever breed for various reasons, morphological and behavioral being primary ones.;

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They are not competent.
The overwhelming majority of what we call species are infertile with each other - as in cannot produce fertile offspring.

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Ok. I'm willing to accept it, thanks for spending the time. Now go to bed!

P.S. I still win the argument though, because of MagicMan's point about ring species! [img]/images/graemlins/tongue.gif[/img]

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Well played then. [img]/images/graemlins/tongue.gif[/img] [img]/images/graemlins/grin.gif[/img]

[vhawk01]

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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.

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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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That's good because I like pancakes, with coffee in a roadside dinner after hiking down the mountainside rocky white with snow.

There is no A-->B-->C case, or even a truly A-->B case. That's the whole point.

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You've managed to talk in a full circle now. Are you seriously saying that a dog and a cat aren't different species? Or simply that they 'always were'? I figured this was the typical micro/macro evolution fallacy, but you did a good job of veiling it until now.

[Matt R.]

Magic_Man,
Interesting scenario.

I think it certainly is possible, yet extremely difficult and unlikely. Basically, it requires a lot of assumptions.

First, you are assuming that this recessive mutation with "no other noticeable effects" can make the individual fertile (or more fertile) with other carriers of the gene and less fertile with non-carriers. It is really unlikely that a single mutation could have such a large impact on the overall reproductive process. It could make them infertile, sure. It could also make them more fertile with respect to some other members of the population. But for it to make them fertile ONLY with other carriers would take quite a mutation. At the very least I would think a phenomena like this would take dozens of interacting genes, probably a lot more. Also note that when you throw in those interactions it increases the complexity exponentially. One mutation can have thousands of potential phenotypic effects, depending on the genetic background.

And even if you have this one mutation, or series of mutation, which increases fertility only with "carriers" of this mutation, you have to consider what happens when the carriers inevitably mate with others of the "non-carrier" set. Now the gene is simply increasing in frequency throughout the population. If the gene is advantagous, it will tend to continually increase in frequency in the population... if it is neutral then random genetic drift is the deciding factor. Therefore this one gene that you're hypothesizing will cause speciation is no longer in just the little subset of carriers. In fact, the "subset" is somewhat ill-defined since they CAN still mate with non-carriers... if they couldn't then we'd already have another species! [img]/images/graemlins/tongue.gif[/img]

Basically, what tends to happen in your scenario is the gene tends to increase in frequency (if advantageous... if not then decrease in frequency) and it causes the ENTIRE population to change. For it to really cause speciation, it would pretty much have to cut that subset off (reproductively) from the rest of the population... which is the barrier to gene flow that I alluded to earlier. I think it would be extremely unlikely for a single mutation or a small set of mutations to cause something like this.

[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.

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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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That's good because I like pancakes, with coffee in a roadside dinner after hiking down the mountainside rocky white with snow.

There is no A-->B-->C case, or even a truly A-->B case. That's the whole point.

[/ QUOTE ]

You've managed to talk in a full circle now. Are you seriously saying that a dog and a cat aren't different species? Or simply that they 'always were'? I figured this was the typical micro/macro evolution fallacy, but you did a good job of veiling it until now.

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No veils necessary. Evolution, as defined above, has issues with logic. That's what's been presented.

[Matt R.]

This could lead to some difficulties, but I will try anyway.

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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.

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I don't like this definition. I think Rduke may chastise me on this one [img]/images/graemlins/blush.gif[/img].

I think a better way to think of it is that ALL individuals are *potentially* fertile with each other. The classificiation of species has nothing to do with potentially fertile. Its useful classification is in terms of probability of being fertile. For instance, if we choose a random human male and human female the probability of them being fertile with one another is pretty high. Much greater than 50% if they have access to modern technology... probably an extremely conservative estimate but you get my point anyway.

If we take two separate species, as a biologist would classically classify it, the probability of them being able to produce fertile offspring is extremely close to zero. But it is non-zero. There is always a chance that if we select one member from species A and one member from species B they can produce fertile offspring. They would have to be of extremely closely related species and probably have high deviations from the "normal" or "average" genotype of the species, but it is at least possible. I think what a biologist typically does is ignore these tiny overlaps because... well they are tiny. It isn't really necessary to consider these occurances when doing research, for instance. A species is a species due to classification purposes... I think it is a mistake to consider it an absolute. I think this may be the issue vhawk is having. But, for a biologist it isn't really necessary to consider the 10^-whatever chance that a random gorilla can mate with a random chimp.

Edit -- the gorilla/chimp example may even be stretching the possibility. But I'm sure there are "separate species" which exist that CAN mate with one another... like with the whole ring species example that was tossed about.

[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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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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That's good because I like pancakes, with coffee in a roadside dinner after hiking down the mountainside rocky white with snow.

There is no A-->B-->C case, or even a truly A-->B case. That's the whole point.

[/ QUOTE ]

You've managed to talk in a full circle now. Are you seriously saying that a dog and a cat aren't different species? Or simply that they 'always were'? I figured this was the typical micro/macro evolution fallacy, but you did a good job of veiling it until now.

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No veils necessary. Evolution, as defined above, has issues with logic. That's what's been presented.

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Even if speciation had issues with logic, (it doesn't - many of the issues here are semantic or other problems of definition), that doesn't mean that evolution has problems. Evolution does not require speciation.

~MagicMan