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Many of the bones and organs found in various species show homologies similar to those described previously. A particular type of homology of interest is what is called a vestigial organ or structure. There is some confusion or controversy over this term. Vestigial does not mean useless or nonfunctional (although vestigial organs could possibly be such, it is difficult if not impossible to prove that any particular structure is actually functionless). The term "vestigial" is used in the sense of an organ no longer or not being used as it is in most other animals. There are homologous structures in various animals that can be identified as being the same basic structure but, in some cases, that structure will be used in a very different or odd manner compared to most of the organisms that have it.
An example of such a structure is the pelvis of whales. All tetrapods (including whales) have pelvic bones. In most animals the pelvic bones are needed in order to be able to move the lower or rear set of limbs for the purpose of locomotion. In some species, such as whales, these limbs don't exist for the most part - although vestiges of them may remain.
Despite this lack of any need for them, whales still have pelvic bones. They are quite small compared to their counterparts in other animals, but they exist. Perhaps they serve some function such as helping to support the whales reproductive anatomy, but there are many different types of structures which would be better suited to such a task.
The question is, why would a whale, which basically lacks lower limbs and doesn't need pelvic bones to move, have pelvic bones that are homologous to creatures that do need pelvic bones to move? Similar homologies exist for snakes and legless lizards. Once again, the only explanation that makes sense is if these creatures evolved from a common ancestor along with all the other tetrapods.
Another common (and frequently misunderstood) example is the appendix. In humans, the appendix has little apparent function, although it now appears that it may store some immune cells. However, the analogous organ in many other species does have obvious function. Moreover, the human appendix is positively disadvantageous in the sense that it is subject to nasty infections that can be fatal. The appendix is a vestigial organ since it does not serve a function like the homologous organs in other animals. So, the question becomes, why do humans have an appendix? (Or why does the human appendix not function like the homologous organ in other animals?) Evolution, the idea that we all have common ancestors, provides a meaningful answer. Creationism does not.
Summary of Anatomical Homologies
In the preceeding two sections you have seen several examples of anatomical homologies - similarities with no apparent functional explanation, between significantly different species. There are numerous other examples that can be found in just about any decent biology textbook. Some homologies can be shown to be positively disadvantageous for the organism that possesses them. Some homologies exist for vestigial structures. (Vestigial structures can also be found at the molecular level as well as the anatomical.) Evolution provides a meaningful explanation for why these homologies exist.
(A bibliographic list of sources and recommendations for further reading will be coming soon...)
This FAQ information provided by Lance F..
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