MadSci Network: Evolution
Query:

Re: Symmetry of organisms

Area: Evolution
Posted By: Dean Jacobson, Faculty Biology, Whitworth College
Date: Tue Mar 4 21:56:51 1997
Message:

In regards to the apparent violation of entropy that some perceive in all organic evolution, it is important to recognize that one must take into consideration TOTAL entropy, not only that of a living organism. As long as entropy increases elsewhere, decreased entropy is allowable, i.e. in the elegant symmetry of animals. (The decreased entropy includes the thermal processes of the sun, and the decomposition of ordered organic food molecules which are oxidized into CO2.).

I am not qualified to comment on the developmental mechanisms of bilateral symmetry, although I have heard that the genetic mechanism for asymmetries (i.e. the heart usually appearing on the left side in mammals) has been uncovered; the default program seem to result in symmetry. I can, however, comment on some mechanisms animals use to perfect and maintain symmetry using sexual selection. In many birds and insects, one sex (usually the female) prefers symmetrical mates. In this way, individuals with mutations or diseases that result in, for example, one tail feather being slightly longer than the opposite feather will be selected against, and these gene versions (alleles) deleted from the gene pool when this individual dies without leaving offspring behind. A wonderful source of evolutionary explainations and discussion is Talk origins at: http://earth.ics.uci.edu:8080/origins/faqs-evolution.html.


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