The California Collection/TheCaliforniaCollection.cdr/his065/homology.arj/HOMOLOGY.DOC

Text File | 1991-01-13 | 7KB | 164 lines

                      HOMOLOGY - Evidence For Evolution?

                        David N. Menton, October 1987

     Since the time of Darwin, the argument from similarity comprises much
of the case for the general theory of evolution.  It is assumed that
similarity proves an evolutionary relationship and the degree of similarity
shows its proximity in time.  This argument has been applied from the gross
anatomical level to the molecular level.

     Creationists argue that similarity is consistent with a common creator
and, moreover, is what one might expect from organisms that live in similar
environments and metabolize similar foods and gases.

EXAMPLES OF GROSS HOMOLOGY:

Sir Gaven de Beer in his book 'Homology, An Unsolved Problem,' points out
that homologous structures can come from entirely different embryonic
origins.  Structures as obviously homologous as the alimentary canal in all
vertebrates can be formed from:

     roof of the embryonic gut cavity - sharks.

     floor of the gut cavity - lampreys.

     roof and floor - frogs.

     lower layer of the embryonic disk, the blastoderm - reptiles & birds.

     "Therefore, correspondence between homologous structures cannot be
     pressed back to similarity of position of the cells of the embryo or
     parts of the egg out of which these structures are ultimately
     differentiated."

de Beer adds that homologous structures are not controlled by homologous
genes except in closely related species.  He concludes:

     "It is now clear that the pride with which it was assumed that the
     inheritance of homologous structures from common ancestors explained
     homology was misplaced."

The use of common ancestry to explain homologous organs can not explain all
homologies:

     The hands and feet on the left are obviously homologous to those on
     the right but surely one didn't evolve from the other.


PROTEIN AND DNA HOMOLOGIES:

     Evolutionists have increasingly despaired of relying on the fossil
record to document the evolutionary descent of organisms.  Molecular
homology is seen as the virtual savior of evolutionary biology.

     Gel electrophoresis -     the proteins of human and chimpanzee are
     about 99% identical.  Does this show common descent through evolution?
     The building materials in a small brick home and the Empire State
     building may also be over 90% homologous; what does this mean?

      There are at least 26 species of the protozoan Tetrahymena, all
      of which are nearly identical in structure, BUT there are
      enormous differences between their homologous proteins.  The same
      is true of the more than 2000 species of fruit flies.

     Comparing selected proteins, evolutionists hope to show not only
phylogenetic relationships but also a "molecular clock" that will provide a
relative time table for evolution. For example:

     alpha chain of hemoglobin differs between horse and man by about 20
     amino acids.  Evolutionists believe that the horse and man "diverged"
     about 100 million years ago THEREFORE, the evolutionary rate of
     hemoglobin is ONE amino acid per 5 MILLION years.    This rate is then
     extrapolated to other differences and in this way a "phylogenetic
     tree" is established complete with DATES!

The National Academy of Sciences in their anticreationist tract "Science
and Creationism" claim:

     "Each of the thousands of genes and proteins provides an independent
     test of evolutionary history."  "- of the many hundreds (of tests)
     that have been conducted NONE has provided evidence contrary to the
     concept of evolution.  Instead molecular biology confirms the idea of
     common descent on EVERY aspect."

It is actually quite difficult to compare gene and protein homologies.
Some proteins are so fundamental to life that they are essentially
identical in nearly all living organisms, "conserved"; other proteins are
nearly species specific.  In all such comparisons there is computer
processing and "weighing" of the data by several different models which are
designed to produce the desired results.  Results which are incompatible
with "known" classical phylogenies based on the fossil record are ignored.
There are in fact many incongruities in the protein homologies:

     LHRH (luteinizing hormone-releasing hormone)-    amphibian and
     mammalian LHRH is identical but DIFFERENT from bird, reptilian and
     certain fish LHRH (which are themselves indistinguishable).  This
     suggests that mammals are more closely related to amphibians than they
     are to birds!

     Cytochrome C - very similar between human and chimp (one amino acid
     difference) but the turtle is closer to the bird than to a snake.

     Calcitonin - lowers blood calcium levels.    Pig and human calcitonin is
     different at 18 out of 32 amino acids (unlike insulin) but man only
     differs by 15 amino acids from the Salmon!


"HOP SCOTCHING" PROTEINS:

     Certain proteins may be found in for example fish and reptiles but not
in amphibians which are supposed to be a phylogenetic link between them.

     hemoglobin - occurs in a few species of insects, some members of some
     families of annelid worms and of course in vertebrates.

     relaxin - a protein that widens the birth canal during birth is found
     in bacteria and protozoa!

     B2 microglobulin - is found in humans, gold fish, lizards, earth worms
     and crayfish but not newts or trout.


In his recent book 'Evolution; a Theory in Crisis': the microbiologist
Michael Denton said:

     "The really significant finding that comes to light from comparing the
     proteins' amino acid sequences is that it is impossible to arrange
     them in any sort of an evolutionary series."

As for determining the date of evolutionary divergence between two
organisms, the situation appears to be no better.  Dr. James Farris, who
developed some of the most used methods for determining "molecular
distance", has concluded that the use of molecular distance data in
phylogenetic analysis is very questionable:

     It seems that the only general conclusion one can draw is that nothing
     about present techniques for analyzing molecular distance data is
     satisfactory .. None of the known measures of genetic distance seems
     able to provide a logically defensible method."

We must conclude that homology is at best ambiguous in its support of
evolution and does not exclude creation.  Phylogenies based on DNA and
protein homologies in particular are often incompatible with phylogenies
based on other methods such as embryology and the fossil record.  There is
a tendency on the part of evolutionists to make much of homologies that
are consistent with evolutionary dogma and to ignore those which are
incompatible.


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