71  Homologous organs
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Similarly-constructed body parts of many living creatures are called homologies. Some examples include the pectoral fins of fish, the front extremities of tetrapod vertebrates as well as the wings of birds and bats. Moreover, all living creatures known to us today are constructed with the same basic building blocks or proteins. The information carrier DNA is also the same for all living creatures. These similarities could indicate a common origin as well as a common creator.


Every creative intelligence has its own specific handwriting. For example, if we consider the pictures and sculptures of Pablo Picasso, we note similarities and a development. However, no one would even think of saying his works have a common descent. Similarities are no proof of common descent. They simply show that the same basic principle was used for different living creatures.

The same applies for DNA strings. The blueprints for similar living creatures are written manifest with the same genetic code, because this code is optimally for all forms of life.


Problems in interpreting similarities:

The interpretation of homologies as an indicator for common descent is concluded only by analogy; however, this is not inevitable. Many similarities can be explained by the function so that a reference to evolution does not provide additional clarification, but rather represents a circular argument (1).

Similarities as indicators for a common descent can be determined clearly only based on empirical data. As a rule, they are recognized as such only under presupposition of evolutionary hypothesis using the principle of economy. Evolution cannot be proven by similarities.


Contradictory genealogies:

Many homologous organs occur in living creatures that can only be very remotely related with one another according to their alleged lineage. For this reason, the majority of coincidental characteristics must be classified as parallel developments in evolutionary theory, which poses significant problems for clarification. There is no generally objective possibility for differentiating between similarity and parallel development. Frequently, characteristics appear to be distributed in the form of building blocks among different species and higher groups (taxa).

Mature organs, organ systems, individual development paths from the egg cell to sexually mature state and genes frequently support contradictory similarity conclusions. This has led to a crisis in the similarity concept because more and more has become unclear, which could serve to support similarities as an indicator for phylogenetic relationships (2).



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References:

(1) Reinhard Junker, Ähnlichkeiten – Rudimente – Atavismen, Hänssler-Verlag, 2002, page 18.
(2) Junker und Scherer, Evolution, ein kritisches Lehrbuch, Weyel, 2006, pages 167–190 and 301.
 
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