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From: howard@53iss6.Waterloo.NCR.COM (Howard Steel)
Newsgroups: sci.bio
Subject: Re: What distinguishes a species?
Message-ID: <207@53iss6.Waterloo.NCR.COM>
Date: 2 Feb 90 13:26:14 GMT
References: <22448@siemens.siemens.com> <202@53iss6.Waterloo.NCR.COM> <7757@cs.utexas.edu>
Reply-To: howard@53iss6.Waterloo.NCR.COM (Howard Steel)
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In article <7757@cs.utexas.edu> turpin@cs.utexas.edu (Russell Turpin) writes:
>>> Are all dogs in the same species?
>> 
>> NO. The main problem is usually physical disparity. When's the last time you
>> saw a St. Bernard - Chihuahua cross?
>
>But a St Bernard will happily breed with a large shepherd <etc down to
							    Chihuahua,)
>If one uses solely the above criterion for being in the same species, one has
>the problem that the relation "being in the same species" is no longer
>transitive.  Hence, the concept of a species (as a group) 
>disappears, to be replaced by the comparative but non-transitive
>relation of breedability.

I agree. The problem is there are so many different critera (from diverse
fields) that at some point the concept of species as you point out disappears.
What I was employing was a simplistic approach, often employed by
anthropologists that the main requirment for a member of a species is the
ability to breed viable offspring. In university the argument that you proposed
was forwarded, and the reply was something like; " but can a St. Bernard breed
with a Chihuahua?" The implication also existed that groups of say people
who were physically separated by insurmountable barriers, effectively became
different species (a ludicrous concept, I realize). The point is species is
a nebulous enough term that it can only be appropriately used within the
context of the field specifically being discussed. A Chihuahua is genetically
in the same species as as a St. Bernard for example, and theoretically nothing
prevents the cross-breeding, except physical constraints. The Chihuahua would 
probably burst with a litter of St. Bernard, and though the reverse doesn't
pose a problem, somebody will have to put the little guy up to it :-).

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