Sex and Species- A Question (was Re: sex)

Peter Herman herman at
Fri Jan 5 08:19:10 EST 1996

Dave Roberts (dmr at wrote:
: Michael F. Hynes wrote:
: [chomp]
: >This definition, while not without its flaws, has the virtue of
: >general application to all organisms. After all when we talk about
: >defining animal species based on "interbreeding to produce fertile
: >offspring", aren't we really talking about sufficient DNA homology to
: >generate chromosome pairing (and recombination ?) ?

: I don't think it is as simple as this (is it ever??).  Many, if not all,
: animal species have many other barriers that have to be matched and
: compatible before the opportunity for chromosome pairing presents itself.

	This is certainly one of the dilemmas.  Michael's suggestion only
deals with the equivalent of postzygotic barriers.  The point that Dave
made (and I just realized that I snipped) about the apparent small number
of species despite the wide genetic diversity cuts to the core of the
problem for me.  
	As a microbial ecologist interested in community structure and
distribution, you see 2 camps.  One says count the classically definable
taxa.  The other says, if it has a different signature when using genetic
tools (RAPIDs, RFLPs or other hybridizations) count it as different.  This
disparity can result in 2 or more orders of magnitude difference in your
estimate of taxa per gram soil! 
	I guess I am somewhere in the middle.  I am extremely
uncomfortable with the extremeists on the side of many taxa.  It is clear
that I have many differences in phenotype compared to other humans, even
caucasions of middle eastern/eastern european extraction.  On an
extremists fingerprinting basis, we would be defined as different taxa
which is clearly incorrect.  On the other hand, classic techniques are
both tedious and clearly underestimate taxonomic diversity.  Real new
insights into the proper arrangement of "genera" such as the old
Psuedomonas, and more recently Rhizobium/Bradyrhizobium have resulted from
analyses of differences in genetic structure.  Unfortunately, this sort of
analysis is just too complex for routine use in soil samples. 
	I guess that is why I brought all this up in the first place!
R. Peter Herman				email	Peter.Herman at
Sveriges Lantbruksuniversitet		Phone:	+46 18 67 12 20
Inst. f. Markvetenskap			Fax:	+46 18 67 27 95
S750 07 Uppsala, Sweden		

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