Criteria for Life

Mark Siddall mes at zoo.toronto.edu
Sun Jan 7 07:35:19 EST 1996


The only workable definition of life is "nucleic acid".
The reason being that this is the substance of the common ancestor of 
all life assuming that all "life" is monophyletic. 
If all life is not monophyletic (i.e., arose more than once) then
there must be more than one biological definition of life.

See how easy that was?
That is to say that biological group definitions must be based on 

monophyly just like "mammal" and "insect" are.

This is not to say that other definitions of "life" are not important.
For example, should we encounter "life", from another planet for 
example we would need a non-biological definition of life to even
recognize it much less deal with it. 

But these other definitions of life are definitively non-biological.
They are metaphysical. 

Mark
-- 
Mark E. Siddall                "I don't mind a parasite...
mes at vims.edu                    I object to a cut-rate one" 
Virginia Inst. Marine Sci.                     - Rick
Gloucester Point, VA, 23062



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