Homology can't be evidence of ancestry if it is defined thus

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Contents 1 Claim 2 Source 3 Responses 4 External Links 5 References 6 See Also 7 Acknowledgments

Claim

Homology is defined as similarity due to common ancestry. The claim then that it is evidence for common ancestry is a circular argument.

Source

1. Wells, J., 2000. Icons of Evolution. Washington DC: Regnery.

Responses

1. Homology doesn't need to be defined in terms of common descent. Originally, homology was defined in terms of the structure and function of the trait in question. It's possible to build a case for evolution using this objective, non-evolutionary definition. This definition was used even by creationists as recently as the mid-1920s (O'Toole, 1926.)
2. The circular-seeming definitions only began to arise after it became clear that common ancestry was best explanation for homologues. While these definitions are generally poor for educational material such as textbooks, their existence does not weaken the actual evidence for evolution from homology. Replacing these definitions with anatomical ones would probably strengthen the teaching of evolution.
3. Modern taxonomy is predicated upon cladistics, which recognizes no necessary relationship between physically similar forms and common descent. In this model, species that resemble each other superficially are not necessarily more closely related. This has already proven to be a more coherent and genetically valid way of representing the "tree of life".
4. add more responses

External Links

• Theobald, Douglas, 1999. 29+ Evidences for Macroevolution: Glossary [1] - defines homology and a related concept 'parahomology'
• The NCSE's critique of Well's homology argument
• Mark Isaak's page for this claim [2]

References

1. O'Toole, George B. 1925. The Case Against Evolution. Chapter 2, pp. 35. The Macmillan Company, New York.

See Also

• Why is Creationism not a Scientific Theory?

Acknowledgments