BSC/PSC

[B.J.Tindall]

To which my reply, as a bacteriologist, is that the cells within a
eukaryote species are constantly dying and multiplying, but we regard the
"cellular assemblage" as the reproducing unit. In the case of prokaryotes
(and unicellular asexually reproducing eukaryotes) we tend to look at the
individual cell..... What do you do with aphids, which do both, or a
population of bees where you have haploid and diplod individuals?

One of the problems, which Thomas Lammers draws our attention to, is where
do we draw the line? Genetically Homo sapiens divides into two distinct
groups which we could define by unique chromosome characters - male and
female - anyone disagree? However, because we know that sexual reproduction
is taking place we would tend to reduce the significance of the X and Y
chromosomes.

As "speciation" takes place you must see changes at the genetic level,
which will manifest themselves at other levels too. However, the question
is whether the genetic diversity reflects two different species or simply
diversity within a species? There was a study recently (PNAS) on various
"ethnic groups" in Europe, including the Celts, Basques, Orcadians, etc.,
which clearly showed the differences within these populations. However,
without the knowledge that the objects under study were members of one
interbreeding population (one gene pool) you may well end up splitting it.

I agree that you can't directly compare a sexually reproducing vertebrate
with an asexually reproducing prokaryote, but as John Locke said in 1689:

"The boundaries of the species, whereby men sort them, are made by men."

True, there are units out there, in nature, which have separated themselves
from other units, and tend to be part of one gene pool, but the problem is
to define what constitutes that "unit". It is a bit like defining the
metre. There is no "natural" definition, so we set the definition and then
you can accurately define any fraction or multiple of it.
Brian

At 01:00 12.11.2003 +0100, Gianluca Polgar wrote:
>I perfectly agree with John's concept of "spatiotemporally diagnosable
>entities".
>
>Obviously BOTH reproductive isolation and morphological characters (whether
>diagnostic or not) of a determinate genetic pool will change with space and
>time through generations, due to evolutionary forces... what is the sense
>of talking of "entities" whose boundaries are continuously changing?
>... IF NOT temporally or spatially defined.
>
>Obviously this should make sense only taking into consideration the
>generation time and numeric amount of the organisms considered, and
>reasoning within a definite spatiotemporal scale. One thing is speaking of
>bacteria, one of sequoias.
>
>Maybe there's no sense in describing a definite bacterial "species" (either
>BSC or PSC), with respect to the generation time (and thus observation
>time) of humans...
>
>Gianluca
>
>
>Gianluca Polgar
>c/o prof. L. Bullini
>Dip. di Gen. e Biol. Mol. "Charles Darwin"
>Rome, Italy
>http://darwin01.bio.uniroma1.it/
>


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