Homology - Evidence For Evolution?

by Dr. David N. Menton, Ph.D.

St. Louis, MO October 1987

Copyright 1991 Missouri Association for Creation, Inc.

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.

PREVIOUS | CREATION INDEX | HOME | NEXT