True Homology - an endangered concept
Since 1859, the principle of homology has been quoted as the singularly most powerful argument in favour of organic evolution. The biological world had been grouped into classes. Organisms within each class exhibit very similar characteristics. Despite being used for rather different purposes, the various organs of the reptile, amphibian and mammal show remarkable uniformity in its organisation or design. Evolution was born out of the belief that such homologous attributes indicate that all these life forms descend from a common ancestor.
Homology in nature can also be explained through faith in the same Creator creating all things. This idea lost favour in the latter part of the 19th century. Believing that our universe was miraculously born became eroded as scientists developed the theory of evolution and began to study nature in the hope of finding evidence to support the theory. Scientists, in general, did not necessarily have this as their agenda, but became engrossed in the study efforts as evolutionary ideas became more popular. Some Christians accept the concept of a common ancestor and see the creative/evolutionary process as the ‘miracle’ - hence theistic evolution.
Recent studies in embryological and genetic research have started to undermine the principle of homology. Homologous organisms exhibiting ‘unity of type’, would be expected to show homologous genes and homologous patterns of embryological development. Such evidence would further support the common ancestor theory. What is being discovered however, are non homologous genetic structures and different embryological development patterns. Once again this is not very common or popular knowledge.
In terms of embryological development, research is beginning to show how homologous structures are arrived at by different routes. From the first cell divisions, the sequence of events in the formation of the blastula in reptiles, amphibians and mammals are obviously different. The blastula itself in all three classes is clearly not identical. The next phase of development is embryo formation or gastrulation. The resulting gastrula in all vertebrates are homologous, however the cells giving rise to the different germ layers and their migration patterns are markedly dissimilar.
After gastrulation, homologous structures (such as the kidney and alimentary canal for example), develop from different sites in the different vertebrate classes. Through research on the common frog, it was discovered that the optic cup was itself the organiser which induced the epidermis layer to form the lens of the eye. By cutting the optic cup of the embryo, no lens developed at all. With an evolutionary mindset, this led scientists to conclude that all vertebrate lenses form in this manner. However, when the optic cup was altogether removed from the embryo of the closely related edible frog, the lens developed all the same. The lenses of the frogs are as homologous a structure as you will find, yet they are formed by completely different mechanisms.
This is clearly a case where Romans 1:20 comes into play; that homologous structures arise out of a multiplicity of methods is testimony to the omnipotence of God. It is interesting that it can be seen so differently depending on the accepted worldview adhered to.
The previous paragraphs discussed the principle of homology as the interpretation that similar characteristics or design in various species indicate that all life evolved from a common ancestor. It was shown how embryological research has however, revealed that homologous attributes in the different classes of vertebrates (or even within the same species) are arrived at by different (non-homologous) routes from non-homologous sites in the embryo. The comment was made that this is a remarkable testimony to God’s omnipotence.
Similar discoveries have been made in the plant and animal kingdoms. Different species boasting incredibly homologous characteristics, achieve this homology via different mechanisms. This is ironic when you consider Darwin’s definition of homology in the ‘The Origin of Species’: Homology is…that "relationship between parts which results from their development from corresponding embryonic parts." As recent research is beginning to discover, this is precisely what homology is not.
As for genetic research, evidence to support the theory of common ancestry is threadbare. For example, many genes appear to affect homologous structures as well as features specific to that particular species. These are called pleiotropic genes in that they serve a multitude of functions. One would expect that the genes associated with homologous structures are exclusive to only homologous features if common ancestry were correct. A mutation in a gene affecting the feathers of a bird also affects the skull of the bird. The skull being homologous to all vertebrates and the feathers not.
There are also many cases of homologous design that cannot possibly be credited to common ancestry. Yet no-one questions the biased logic. The similar pentadactyl design in the forelimbs of all terrestrial vertebrates is uncanny. However, the forelimb and the hindlimb of all vertebrates also follow the same pentadactyl design. No scientist would dare suggest that the forelimb evolved from the hindlimb (or vice versa) as it is accepted that these evolved independently from the pectoral and pelvic fins of the fish. And this by random accumulations of tiny advantageous mutations. It is hard to believe that there is some adaptive necessity in the pentadactyl design. And if there was, that random mutations could hit on it more than once. There is still no satisfactory scientific explanation for ‘unity of type’.
The fish-like appearance of the whale resulted in its original classification as a fish. This is a classic example of how analogy can so easily be mistaken for homology. Modern advances in embryology and genetics are dwindling the number of cases of true homology implicating the uniqueness of species. Sometimes a special creation is more credible than the alternative. Or as Michael Denton puts it…
…The same deep homologous resemblance which serves to link all the members of one class together into a natural group also serves to distinguish that class unambiguously from all other classes. Similarly, the same hierarchic pattern which may be explained in terms of a theory of common descent, also, by its very nature, implies the existence of deep division in the order of nature. The same facts of comparative anatomy which proclaim unity also proclaim division; while resemblance suggests evolution, division, especially where it appears profound, is counter-evidence against the whole notion of transmutation.