What prevents evolution?

[Sephus]

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Wonderful, but as a given member of A1 diverges in terms of reproductive compatibility from A, it simultaneously diverges from the other members of A1. Thus, A1 becomes internally infertile.

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how does a "member" diverge from the group in terms of reproductive compatibility?

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According to the same process causing all successive generations to tend to diverge: genetic drift.

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i assumed "member" referred to a single organism. it refers to a subgroup of A1? oh, it must refer to a "lineage." the reason it doesn't "drift" away from A1 is that it's not isolated from the rest of A1. A1 keeps on interbreeding.

if organisms from group A1 all live together and interbreed, if they "drift" they drift together, right? what's the pressure causing them to split into A1a and A1b?

the only reason A became A1 and A2 is that they became isolated from each other, right?

[Skidoo]

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Some individual in A1 undergoes a mutation that makes them infertile with the rest of A1. They die.

This repeats endlessly until A1 is extinct.

This doesn't make any sense. If this could happen, why would it wait until the groups are separated to start occurring? Under this assumption, every species on earth should go extinct by becoming internally infertile.


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Yes, in exclusive terms of the process of mutation of the genome without some mechanism of repair.

As for A becoming A1, it does not matter how small the increments are. Your first bone fide instance of "speciation" in A1 is where your problem lies.

The propagation of alleles per se is not the issue, rather it is how a new group A1 can be developed from A. It's no use trying to sneak anything through using gradualism. What remains a necessity under all conditions is the continuity between parent and offspring such that the latter is reproductively compatible with (the other offspring of) the former. Otherwise, what has been produced is itself incapable of having offspring.

You are still faced with the problem of the reproductive discontinuity necessary for one mutually fertile group to develop into another.

[Skidoo]

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Wonderful, but as a given member of A1 diverges in terms of reproductive compatibility from A, it simultaneously diverges from the other members of A1. Thus, A1 becomes internally infertile.

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how does a "member" diverge from the group in terms of reproductive compatibility?

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According to the same process causing all successive generations to tend to diverge: genetic drift.

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i assumed "member" referred to a single organism. it refers to a subgroup of A1? oh, it must refer to a "lineage." the reason it doesn't "drift" away from A1 is that it's not isolated from the rest of A1. A1 keeps on interbreeding.

if organisms from group A1 all live together and interbreed, if they "drift" they drift together, right? what's the pressure causing them to split into A1a and A1b?

the only reason A became A1 and A2 is that they became isolated from each other, right?

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A member is a single organism, but the same reasoning would apply to a subgroup as well.

The capacity of a group to genetically drift as a unit is key to the entire problem, and what makes or breaks either side of the argument.

Thanks for that contribution, as it represent a clarification of the entire issue making all the back-and-forth worthwhile.

I'll consider it.

[Sephus]

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Your first bone fide instance of "speciation" in A1 is where your problem lies.

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it's not in A1, it's between A1 and A2.

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Yes, in exclusive terms of the process of mutation of the genome without some mechanism of repair.

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there's no need for "repair" in the sense of "returning to the original configuration." the population just needs to stay fit.

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What remains a necessity under all conditions is the continuity between parent and offspring such that the latter is reproductively compatible with (the other offspring of) the former. Otherwise, what has been produced is itself incapable of having offspring.

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you can't be serious. each population stays homogenous enough to continue reproducing. A1 breeds with A1 just fine. A2 breeds with A2 just fine. but they're isolated from each other, so there's nothing keeping them the same.

[Skidoo]

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Yes, in exclusive terms of the process of mutation of the genome without some mechanism of repair.

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there's no need for "repair" in the sense of "returning to the original configuration." the population just needs to stay fit.

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Not "repair" necessarily in those terms. The group must remain fit with respect to its environment, true enough, but each member must also remain reproductively compatible with other members of the group. There are two considerations.

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What remains a necessity under all conditions is the continuity between parent and offspring such that the latter is reproductively compatible with (the other offspring of) the former. Otherwise, what has been produced is itself incapable of having offspring.

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you can't be serious. each population stays homogenous enough to continue reproducing. A1 breeds with A1 just fine. A2 breeds with A2 just fine. but they're isolated from each other, so there's nothing keeping them the same.

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Concerning these and similar comments of yours, I have the following response. Each mutation effecting fertility between A and A1 passed throughout the descendant group also contributes a gradual degradation in fertility within that group just as it diverges each member individually from reproductive compatibility with the progenitor group (speciation). The isolated offspring become mutually infertile simultaneous with their collective divergence in fertility from the original group.

[Sephus]

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Each mutation effecting fertility between A and A1 passed throughout the descendant group also contributes a gradual degradation to the mutual fertility within that group just as it diverges each member individually from reproductive compatibility with the progenitor group (speciation).

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i'm sure this thread has made a complete circle by now.

all the small changes brought about by mutations/natural selection are passed around A1. after lots of generations, many small changes have occurred within the population. taken individually, these changes generally don't harm the reproductive ability of the organisms, otherwise they wouldn't stick. taken as a whole, though, A1 has changed too much to breed with (you're calling it A, i like to call it A2).

you can choose not to believe it, a lot of people do that, but the only way for you to defend the position that it can't/doesn't happen is to do it with scientific knowledge about reproduction/DNA. intuitively, it makes sense that an arbitrarily large number of small changes can add up to a big change. i can't go very far beyond that because it's not my area.

[Sephus]

basically, if what you're saying is true, you could take a population of organisms and have them all interbreed for a trillion generations in a variety of habitats and if, after all that, they were still around, they would still be similar enough to the originals to breed with them.

it's possible you're right, but it looks like we've finally reached the point where we're just stating opinions. what's your background in biology like?

[Skidoo]

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taken individually, these changes generally don't harm the reproductive ability of the organisms, otherwise they wouldn't stick.

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The changes accumulate, with no one in itself being necessarily decisive. So they stick.

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taken as a whole, though, A1 has changed too much to breed with (you're calling it A, i like to call it A2).

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The compatibility between A and A1 is what is matters to speciation. What happens with A2 is a corollary.

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you can choose not to believe it, a lot of people do that

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What's arbitrary here is assuming that randomly occurring mutations effecting fertility within a group are somehow different than their equivalents when the observed population consists of individuals from different groups.

[Nielsio]

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This is a question for NotReady and anyone else who would care to answer. In another thread NotReady claimed that "atheistic" evolution wasn't science (I'm not sure what "atheistic" has to do with it--is that like atheistic gravity or atheistic plate tectonics?).

So let me pose this question. If you have:

a) Self-replicators organisms whose phenotype (i.e. their internal and external structures, organs, behaviors, etc) depends on their genotype (a genetic code that contains the "recipe" for growing the organism), and

b) The fidelity of their genetic replication is good but not perfect (i.e. errors are made), and

c) Small difference in the genetic codes of two similar organisms can lead to small differences in phenotype (not that all small difference in genetic code must necessarily lead to small difference in phenotype; some small difference in genetic code lead to huge differences in phenotype, and some small, and even large, differences in genetic code do not lead to any phenotypic difference at all), and

d) The differential reproductive success of individuals replicators within the population depends to any extent on phenotype, then

Evolution is inevitable.

So, what prevents evolution from occuring? If if it does occur, how can you claim that it "isn't science" ?

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It is inexplicably presumptuous and foolish to believe that the above in any way necesitates 'evolution' as most on this forum understand it.

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"I don't accept your logic, and you suck"

[Rduke55]

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Wonderful, but as a given member of A1 diverges in terms of reproductive compatibility from A, it simultaneously diverges from the other members of A1. Thus, A1 becomes internally infertile.

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how does a "member" diverge from the group in terms of reproductive compatibility?

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According to the same process causing all successive generations to tend to diverge: genetic drift.

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i assumed "member" referred to a single organism. it refers to a subgroup of A1? oh, it must refer to a "lineage." the reason it doesn't "drift" away from A1 is that it's not isolated from the rest of A1. A1 keeps on interbreeding.

if organisms from group A1 all live together and interbreed, if they "drift" they drift together, right? what's the pressure causing them to split into A1a and A1b?

the only reason A became A1 and A2 is that they became isolated from each other, right?

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That and this:

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you can't be serious. each population stays homogenous enough to continue reproducing. A1 breeds with A1 just fine. A2 breeds with A2 just fine. but they're isolated from each other, so there's nothing keeping them the same.

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are really the main relevant points here. I think Skidoo is not taking this into account. Genetic drift is the change of gene frequencies in a population.

Well put Sephus.