sexuality & Trees of Life

[Ken Kinman]

     I would agree that asexual species clearly "exist", as much as sexual
species "exist", and that a phylogenetic or phenetic species concept needs
to be used for the difficult task of delimiting such asexual species as
unarbritarily as possible (and timely studies of many sexual species as
well, given limited resources).
     However, I think it is **extremely** misleading to say that sexual
reproduction is limited to a "small section of organisms".  In terms of
species diversity, far more species are sexual than are asexual, and far
more biologists study sexual organisms than study asexual ones.
     That is just one of many problems with looking at Woese's "Tree of
rRNA" as a true Tree of Life.  In the first place, it completely trivializes
the vast diversity of Metaphyta and Metazoa (developmental diversity,
structural and species diversity, and so on).  This seems pretty obvious.
But what has almost completely escaped the attention of biologists thus far,
is that Woese's view also greatly trivializes Eubacterial evolution as well
(and worse yet greatly skews their phylogeny).  Microbiologists should
Woese's paradigm as a double-edged sword at the very least.
     Far more natural trees of life will be produced in the future, and rRNA
distances certainly will not be the sole criterion.  Then it will become
obvious that Woese and his Three Urkingdoms/Domains swung the classificatory
pendulum too far (and that it did cause a great deal more damage and
confusion than one could have readily imagined in the 1990's).  Re-read this
message ten years from now, and I think it will be very apparent by then
(same goes for the "thermophilic origins" idea as well).
                             -------Ken Kinman
*********************************************************
>From: "B. J. Tindall" <bti at DSMZ.DE>
>Reply-To: "B. J. Tindall" <bti at DSMZ.DE>
>To: TAXACOM at USOBI.ORG
>Subject: Re: BSC
>Date: Mon, 15 Nov 1999 14:10:35 +0100
>
>Interesting to see what problems the "biological species concept" is
>producing. Just to throw the debate open a little more; the problems
>encountered in zoology and botany are those caused by not knowing where to
>draw the line with sexually breeding "species". Of course the definition is
>loaded in favour of sexual reproduction. One often hears that organisms
>which do not breed sexually do not have species, because they do not fit
>the "biological species concept". The problem is that asexually reproducing
>organsims seem to have been very successful in evolution, in fact a quick
>glance at molecular estimates of evolution would suggest that sexual
>reproduction is only reserved for a rather small section of organisms.
>Perhaps one must come to terms with the fact that the "biological species
>concept" is a "biological species concept for sexually reproducing
>organisms", and that there should be other concepts for dealing with the
>asexual organisms. After all if "speciation" is one of the first steps in
>the divergence of one "species" into two or more "species" which is part
>evolution, then asexual organisms also evolve and must be subject to the
>"asexual equivalent of (sexual) speciation".
>Brian Tindall
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