On Fri, 14 May 2004 05:13:34 +0000 (UTC), ragland37{at}webtv.net (Michael
Ragland) wrote:

>
>Species- One kind of organism. Of sexually reproducing organisms, one or
>more natural populations in which individuals are interbreeding and are
>reproductively isolated from other groups.
>
>
>Is this a sufficient definition of species? I've been reading some of
>the controversy over this term and as far as I can see this is an apt
>definition of biological species. It doesn't take anybody with a little
>general knowledge of Darwinism and embryology that we were once
>"different" species. Over a long gradual period of time we evolved from
>other life forms or "species". If one sticks to our current definition
>of species I think there is no contadiction with evolution. However,
>strictly in terms of evolution the term "species" is fluid and ever
>changing. There is no question, assuming we don't destroy ourselves,
>that in a billion years we won't resemble anything like what we do now
>in terms of internal and external morphology. Nevertheless, as
>incredible as it may seem there will likely be vestiges of us remaining
>a billion years from now...to use an analogy like the human embryo at a
>certain early stage briefly resembles or is like a fish. 
>
>There is no question evolution can be externally influenced by future
>genetic engineering and this in itself will be a new form of evolution.
>Natural selection won't be controlled but will be gradually influenced
>and at some point in the far off future replaced completely by
>artificial selection via genetic engineering. 
>
>Does everybody agree with the aforementioned definition of species? Do
>people agree on an evolutionary scale the term and meaning is fluid and
>subject to change?
>

There are many definitions of "species", useful to different
categories of biologist under different circumstances. The "biological
species" definition you give above is usually attributed to E. Mayr
and is particularly useful for understanding the processes of
evolution (the reason why this particular definition was created).
However it really isn't at all practical for field work, where the
"morphological species" is usually used.  There are ecological
species, phylogenetic or "Hennigian" species, etc.  Look at the book
edited by Wheeler and Meier, "Species Concepts and Phylogenetic
Theory: A Debate"
  http://www.columbia.edu/cu/cup/catalog/data/023110/0231101422.HTM

Biology has a tricky way of generating weird organisms that defy all
our clever ways of sorting and categorizing and explaining them. No
matter what basic "rule" or"law" you invent in biology, somewhere
there will be a living thing that violates your rule or spans your
categories.
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