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From: eddy@boulder.UUCP
Newsgroups: sci.bio
Subject: Re: Life Classification ...further comments
Message-ID: <1264@sigi.Colorado.EDU>
Date: Wed, 3-Jun-87 12:40:49 EDT
Article-I.D.: sigi.1264
Posted: Wed Jun  3 12:40:49 1987
Date-Received: Fri, 5-Jun-87 01:01:07 EDT
References: <9543@duke.cs.duke.edu> <1125@ius2.cs.cmu.edu>
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Reply-To: eddy@boulder.Colorado.EDU (Sean Eddy)
Organization: University of Colorado, Boulder
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In article <2172@husc6.UUCP> gallagher@husc4.UUCP (paul gallagher) writes:
>One question that interests me is this (I don't know the answer):
>If you define a species as a group of populations among which genetic
>information is freely exchanged, then what are the species of bacteria?
>Maybe the whole kingdom is a single species by this definition?!

Answer: you *don't* define a species as a group of populations
among which genetic information is freely exchanged. Too many
examples exist in the animal world (and horrendous numbers in
the plant world) of so-called 'species' inter-breeding; don't worry
about the bacteria!

Question: How *does* one define species? On the "seemed like a good
idea at the time" principle? I really don't believe there's a
good, hard rule; I'd like to hear one.

(Technically, I don't believe all the bacteria exchange information.
Most cases of 'natural' bacteria transformation involve a live
bacterium of one species picking up exogenous DNA from a
bacterium of the same species, and incorporating that DNA by
homologous recombination. Some species, like Craig's example
of Hemophilus influenzae, are so picky they will only a small
fraction of the DNA from their own species. 

In any case, I believe the restrictions imposed by homologous recombination
would tend to prevent free genetic exchange between all but the
most closely related bacteria.)

- Sean Eddy
- Dept. of Molecular, Cellular, Developmental Biology
- Univ. of Colorado, Boulder; Boulder, CO 80309
- eddy@Boulder.Colorado.EDU		!{hao,nbires}!boulder!eddy	
- 
- "It all seemed to make some sort of sense at the time."
-					- Arthur Dent