From: lamoran@gpu.utcs.utoronto.ca (L.A. Moran)
Subject: Molecular Homologies
Organization: UTCS Public Access
Date: Tue, 13 Oct 1992 03:37:25 GMT


Alan M Feuerbacher wrote,

     "Indeed, in a larger perspective, the close resemblance of human
      and chimp DNA really represents another evolutionary problem,
      rather than a solution.  Comparisons of DNA in frogs show that
      there is much greater DNA variation among them than there is
      between the bat and the blue whale; yet the world's three
      thousand species of frogs are all much more similar to each
      other than man is to any of the other primates, to say nothing
      about comparing bats and whales."

I believe that Alan is referring to an old problem in molecular biology that
goes by the name of the "C-value paradox". The so-called paradox is that
oraganisms that are very similar morphologically can have very different
amounts of DNA (the amount of DNA in one complete set of chromosomes is
called the C-value). Some of the most obvious examples are seen with frogs
that differ in DNA content by factors of two or four even though they look
pretty much the same. The explanation is that some organisms have doubled
the size of their genome and that this does not have much effect on their
overall morphology. Another explanation of the "paradox" is that much of
the DNA in some organisms is junk.

Alan's suggestion that the world's three thousand species of frogs are all
much more similar to each other than man is to any of the other primates
is a classic example of anthropomorphism. Most biology books will have 
pictures of some of the strange and exotic species of frogs - they sure look
different to me! I wonder if these frogs see much of a difference between
us and monkeys?

Loren I. Petrich also responed to this point by saying,

     "Good grief!!!

      In macroscopic features, the batrachians (frogs and toads) are 
      more similar in overall appearance than our species and the great
      apes. There was even an article in _Science_ some years back that  
      reported on comparing human and chimp skeletons by the same kinds of
      measurements as are used to classify frogs. The result: more
      difference."

I don't agree. It seems to me that the tree frogs of the South American rain
forest are very different from the bullfrogs that I am familiar with, even
though they share many features. It's a silly argument in any case.

Alan M Feuerbacher expands on the point that there are greater differences
at the molecular level between species of frogs and species of primates. 

      "... The author of virtually every contemporary book supporting 
       evolution trots out the human-chimp DNA comparison, but very few 
       mention the frogs or another discovery of microbiology that has 
       been known for some time."

Species of frogs diverged from each other a long time before humans and chimps
had a common ancestor. Therefore, evolution predicted that frogs would differ
at the molecular level by a greater amount than primates. The prediction 
turned out to be correct. Alan does not understand evolution. BTW, the 
differences that I am referring to are not the same as the C-value differences
mentioned above. 

Laurence A. Moran (Larry)

Newsgroups: talk.origins