Re: Scientific theory

Randy Isaac wrote:

"I think that out of a number of tests [of the theory of evolution], there are two that I find striking:
1) the theory of common descent predicts that all living organisms have DNA based on the same four, and only these four, nucleotides.
2) it also predicts that all naturally occurring DNA will have the same (left-handed as it turns out for unknown reasons) chirality."

I'm going back to this because, if you use these arguments as significant "proofs" of the theory of evolution, you at least need to be aware of the questions you are begging. Since no one with more competence in the field has addressed this, I take on the responsibility.

Test 1 (four nucleotides) would be meaningless unless DNA could function with different nucleotides than the known four. But nobody knows this. Given all the churning of genetic codes that must have gone on over the billions of years, it would be surprising if no instances of different nucleotides ever occurred. If they haven't, a likely implication is that DNA can't function with different nucleotides. If so, DNA of all organisms would have the four nucleotides whether or not all organisms had a common origin.

The chirality result (Test 2) is harder to argue against on this basis. However, if life originated only a few times, chances of starting with the same handedness in every case would be pretty good, so handedness still would not necessarily imply a common origin.

These predictions address the question of whether all life had a common origin. But if we extend the question into the theological realm, which we like to do, then satisfaction of neither prediction is necessarily of any value: For example, a creationist who believed that different life forms were specially created at different times could say that (1) God determined beforehand that DNA with the four nucleotides was the preferred solution and (2) God likes left-handed rotations.

I claim it's difficult or impossible to make a good case for evolution purely on the basis of DNA. Without the fossil evidence, such arguments would merely generate breeze. They have limited merit because there is fossil evidence.

Don

  ----- Original Message -----
  From: Randy Isaac<mailto:rmisaac@bellatlantic.net>
  To: asa@calvin.edu<mailto:asa@calvin.edu>
  Sent: Tuesday, December 07, 2004 6:19 PM
  Subject: Re: Scientific theory

  "Not to argue with you, Randy, as I believe in evolution in a Christian
  context, but can you discuss a test of the theory of evolution which it
  has passed, thus demonstrating for all to see that it has been
  scientfically proven?

  Thanks,

  --Bill Yates"

  I think that out of a number of tests, there are two that I find striking:

  1) the theory of common descent predicts that all living organisms have DNA based on the same four, and only these four, nucleotides.
  2) it also predicts that all naturally occurring DNA will have the same (left-handed as it turns out for unknown reasons) chirality.

  To my knowledge, no instance has been found that violates either one of these. And I don't know of any other theory of origins that would make the same definitive prediction, though one might rationalize why it should be so. No, Darwin didn't know about DNA structure so this prediction came later, but there's an incredible amount of data that's been collected since DNA was discovered and it all seems to fit--so far.

  I'm not saying whether I believe in evolution or not. But let's not reject it on the grounds that it isn't scientific or that it isn't testable.

  Randy
Received on Fri Dec 10 03:59:45 2004