What prevents evolution?

[hmkpoker]

Question for Rduke:

Are the premises and logic in the OP sufficient, in your opinion, to conclude that evolution is fact?

[vhawk01]

This is the reason I objected to the term speciation in the first place. It causes people to believe there actually are lines, and while it usually appears there are lines in SPACE, when we consider whether there are lines in TIME it becomes obvious. Clearly, the line of generations between human/chimp ancestor and me has NO lines. At no point does one change into a different species. Its just because all the intermediate groups are dead that it APPEARS there is a line. Skidoo is then free to attempt to use these imaginary lines to make his arguments. They don't exist. Just like piles don't exist, at least not if you want to make the argument that a grain of sand can't turn into a pile.

[Rduke55]

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Question for Rduke:

Are the premises and logic in the OP sufficient, in your opinion, to conclude that evolution is fact?

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I would say so, and you could do one for drift too. (which I guess, has been dominating the thread recently)

[Phil153]

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Question for Rduke:

Are the premises and logic in the OP sufficient, in your opinion, to conclude that evolution is fact?

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I would say so

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[arahant]

Skidoo - You seem to be treating 'fertility' as an all or nothing proposition, which it isn't. The following is a more detailed explanation of how two groups (initially identical) can become infertile with each other, while maintaining their own fertility within the group.

I will number the steps, so that if you have an objection to this process, you can easily isolate the step you object to.

This is long, but apparently neccessary. (I'm probably wasting my time, but I'm going to take some pleasure in explicating the mechanism, and maybe someone here can use it to help teach a bio class or something [img]/images/graemlins/smile.gif[/img] ...ANYWAY>>>

1) Let's start at the point where the group has separated into swamp and dessert, and call the new groups A and B. Group B lives in an area with no ambient radiation, and never, ever mutates.
2) For the sake of specificity, WLOG, let's use mammals for this example.
3) At the beggining of this process, all individuals are essentially identical, genetically.

4) Reproduction occurs through standard intercourse...a male deposits sperm into a female...one of these sperm comes into contact with an egg, and using proteins on the suface of the sperm and egg, they merge.

5) Now consider a change in population A, currently located in the desert, and next to a uranium ore deposit (for humor only). Let's say that on average, there are 2 basepair substitutions that affect the coded proteins in each member of A in every generation. They occur in the production of sperm and eggs, and don't affect the parent's phenotype, and they occur randomly.

6) Each substitution results in a change in a single amino acid in the resulting protein.

7) One of the males in the population develops the following 2 mutations, with the following effects:
7a) A single amino acid in the 1000AA surface protein on his sperm is replaced. This makes the likelihood of successful mating 95% of the previous level because the protein is not as compatible with the female protein,making it less effective in 'latching on' to the females eggs.
7b) A single amino acid in a protein responsible for kidney function reduces the amount of water excreted by the animal by 20%. WLOG, this increases the ability of the offspring to make it to adulthood by 20%.

8) The male does his thing, attempting to impregnate 100 females (these are very slutty animals)

9) Again, WLOG, let's say that before he was always successful, and each child had a 50% chance of reaching adulthood. So before his mutations, he would have had 50 children in the next generation.

10) But now, we have mutations...he only fathers 95 children, but because they excrete less water, 59 of them become adults.

11) Note that at this point, we have an animal that is 'less fertile' but MORE successful at reproduction.

12) So these two mutations spread through the population...after 100 years, all the males have the same sperm, and both males and females excrete less water.

13) Now a female has a few mutations...One mutation makes her egg proteins more compatible with the new male mutation, and one makes the offspring have less fur. Similar to the prior example, she is more likely to breed, and more likely to have offspring that survive.

14) This process continues ad infinitum. After it has occured 100 times, the sperm and egg proteins of population A are still well-suited for each other. They hook up nicely, and the sperm enters the egg.

15) But because each protein has 100 amino acids of difference with the group B proteins, Group A males are totally incapable of getting their sperm to penetrate the eggs of Group B females.

16) QED.....

[Rduke55]

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Question for Rduke:

Are the premises and logic in the OP sufficient, in your opinion, to conclude that evolution is fact?

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I would say so

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?
Maybe fact is a bad word.
Are you more comfortable with the term "inevitability"?

[Sephus]

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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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i want to kick you in the nuts for this reply. A has split into two populations, A1 and A2, remember? there's no reason to talk about A1's compatibility with A1.

[Rduke55]

And "phenotypes are heritable" can be up there (although I'm assuming that's an assumption since we are talking about the units of heredity).

[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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The issue I'm raising only deals with the relationship between A1 and A2 indirectly, but since it keeps coming up, I'll address them. In order for A1 and A2 to be mutually infertile (the sense of "speciation" used here), either or both of them must become infertile with A. The logic of that is plain enough, I hope. In any case, group A still has to produce a descendant group with which it is infertile. That is why it is only necessary for me to address A to A1, while ignoring A1 to A2, to make my point.

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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.

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My use of the term "genetic drift" was actually not quite correct in that it's too narrow for what I'm trying to get at. Substitute random mutation, often effecting fertility. Maybe I was a bit hasty, but it should be easy to clarify.

The principle at play here is akin to isotropic expansion. If A1 diverges in it's reproductive compatibility from A, what would stop the same tendency from operated within A1? If you say the propagation of such mutations within the isolated group will preserve its homogeneity, that's fine. However, if a mutation carries with it a tendency to reduce fertility without otherwise improving adaptation (and there's little reason to assume otherwise), merely duplicating the basis of that tendency in a potential reproductive partner does not necessarily correct the problem. In other words, two wrongs don't make a right. A mutation tending to produce infertility or, generally, reproductive incompatibility is only in the most extremely improbable case going to be compensated for by its duplication in the opposite member. Thus, the same process pulling A1 from A also pulls apart A1 and prevents true speciation.

[Rduke55]

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what would stop the same tendency from operated within A1?

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Yes, because the group drifts together.

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However, if a mutation carries with it a tendency to reduce fertility without otherwise improving adaptation (and there's little reason to assume otherwise)

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OK! Now I'm seeing why you're confused.
This is not the case. We are not talking about these mutations reducing fertility on its own or as a whole. Mutations cause infertility between the groups because of the effects these changes have on gene alignment etc.
Their genomes become incompatible with each other.

You can have mutations in a group that increase fertility within that population yet reduce the fertility with the other group. In fact, you would expect this to happen.

So this:

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Thus, the same process pulling A1 from A also pulls apart A1 and prevents true speciation.

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is wrong.