What prevents evolution?

[Alex-db]

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because dna changes over time, A is "more similar" to B than to C.

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The DNA can't somehow coordinate its changes to retain fertility WITHIN each generation while at the same time producing infertility BETWEEN generations. What do you suggest as an additional mechanism, remembering the objections I have already raised?

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I haven't read that book, but I guess it says something like this, since it seems fairly straight forward:

Assume the parents are representative of an 'average' of the offspring. So 90% reproductivity with the parents means an average of 90% with each other as well. Say the true range is 80% to 100%

Since reproducing requires reproduction, in this question of inheritance it is only sensible to consider the members of a generation who actually reproduce.

Therefore:

When considering a generations' parents, the reproductive % between those parents appears to tend towards 100%, even though the range within that generation was 80-100% and had a difference from its parents of 90%.

(THE ONES THAT COULDN'T REPRODUCE DIDN'T REPRODUCE!)

This no logical basis for expecting reproductivity within a generation to reduce.

This is actually beautifully intuitive if you take a moment to understand it. The simplicty is what makes evolution almost certainly inevitable.

[Hopey]

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When considering a generations' parents, the reproductive % between those parents appears to tend towards 100%, even though the range within that generation was 80-100% and had a difference from its parents of 90%.

(THE ONES THAT COULDN'T REPRODUCE DIDN'T REPRODUCE!)

This no logical basis for expecting reproductivity within a generation to reduce.

This is actually beautifully intuitive if you take a moment to understand it. The simplicty is what makes evolution almost certainly inevitable.

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It *is* beautifully intuitive if you take a moment to understand it...as long as you don't believe accepting it constitutes a sin. That's where Sharkey/Skidoo's hang-up is -- he *can't* accept evolution, as he believes accepting it would go against his religion's teachings. So he fights tooth and nail to ignore the evidence, and keeps moving the goal-posts so that he never has to admit that he could be wrong.

There can be no other explanation as to why he continues to be so obtuse.

[Skidoo]

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So 90% reproductivity with the parents means an average of 90% with each other as well. Say the true range is 80% to 100%

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That's about right. As the capacity to reproduce with the reference generation approaches zero, its few remaining descendants are no longer fertile amongst themselves either and so die out. If you're implying that those closer to 100% fertility within generations will find each other and so maintain the group, that's not enough. Any net accumulation of errors not corrected for, which selection doesn't do either, leads to the same inevitable outcome.

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Since reproducing requires reproduction, in this question of inheritance it is only sensible to consider the members of a generation who actually reproduce.

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There are fewer such individuals as the generations progress due to the said tendency of the genetic basis of reproductive capacity to diverge. Considering only a fertile subset of each subsequent population doesn't remove the constant erosion to the underlying mechanism. Saying divergence is always being selected against doesn't provide a corrective to random change. It only realizes the consequences.

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(THE ONES THAT COULDN'T REPRODUCE DIDN'T REPRODUCE!)

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Yeah.

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This no logical basis for expecting reproductivity within a generation to reduce.

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Of course there is: exactly the same process causing reproductive capacity between generations to be reduced.