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Re: More on the genus problem

I have never heard a good definition for what a species is.

Reproductive compatibility doesn't apply to single celled organisms...

Hybrids of species considered separate are occasionally fertile (mules, Ligers, 

Regarding the dog example with a chihuahua and a Great Dane - it is argued one 
or more intermediate dogs can interbreed with them both, so they are both 
members of the same species.

If we were to kill all dogs except Great Danes and Chihuahuas, would they then 
suddenly be two different species?
What if said intermediate dogs are in existence, but isolated from either 
group? Are they still 2 species? If the isolation ends, do they become the same 
species again?

Did there ever exist a transitional human form that would be able to interbreed 
with humans, and with chimps? If such a form existed, would that make us the 
same species?

We try to classify things into groups that make sense, but its really hard to 
make exact rules for such classification.
Its as if each organism is a weird shape on a Venn diagram, and where most of 
these individuals overlap, we group those into a species (or sub-species, or 
breed, or race).
So then you have these regions where individuals overlap, and those regions 
themselves overlap, so you take the regions that seem to overlap with each 
other, and call that a species or genus, and so on up the tree.

Phylogenetically, each individual would be like their own branch, and the 
traditional branches are really like intertwined vines.
And of course, there is the "web" rather than "tree" analogy to take into 
account gene flow.

Its all a big mess, as I said, I've never heard a good definition for a 
species, so I wouldn't expect a good one for a genus.

It is whatever is convenient for classification.

--- On Sun, 9/20/09, Augusto Haro <augustoharo@gmail.com> wrote:

> From: Augusto Haro <augustoharo@gmail.com>
> Subject: Re: More on the genus problem
> To: "DML" <dinosaur@usc.edu>
> Date: Sunday, September 20, 2009, 11:13 AM
> > In order to confirm contribution
> to the same
> > gene pool, you should have a living holotype and prove
> if an
> > individual you collect can have fertile offspring with
> it (at least
> > conforming to the laboratory definition: this may
> imply we will likely
> > few times be sure if a given individual contributes to
> the wild gene
> > pool) -continuing this absurdity, given that the
> holotype will
> > sometime die, you will have to clone it regularly-.
> Now that I think, not even this will serve to put into
> different
> species. It is not necessarily true that if an individual
> does not
> reproduce with the holotype they are parts of differente
> gene pools,
> because of clines. Then, we should also see if the specimen
> leaves
> fertile offspring with individuals which leave fertile
> offspring with
> the holotype, which in principle comes from what we
> perceive as the
> mid-point of the distribution of the contributors to the
> gene pool, or
> with individuals which are somewhat intermediate in shape
> or size
> (Great dane and Chihuahua - or more naturally, wolf and
> coyote,
> because the reproductive interaction will more likely be
> replaced by
> killing/predation if the size disparity between both is
> large).