[EBB Sightings] two strange Lake Merritt geese

On Fri, 09 Dec 2005 09:09:42 -0800, Hilary Powers 
wrote:

>Geese and ducks are sufficiently, ah, undiscriminating - and successful 
>- to bring the whole question of species identity as I learned it in 
>high school biology into question. We draw lines, but the real world 
>doesn't care about them all that much.

Actually, I think the real world cares a lot about species limits.  The
modern biological species concept is merely a reflection of real-world gene
flow and real-world conditions.  

Individuals belonging to the same species interbreed readily with no
selective disadvantage to their offspring. Individuals of different species
may hybridize occasionally where they come into contact, but these hybrids
are either rare or at a selective disadvantage.  They need not be
infertile.  Infertility is merely one type of selective disadvantage.
There are many others.

If the real world didn't care about species, there soon would be no
diversity at all.  Over time, without species boundaries, natural selection
would reduce all life to just one species.  It is the very existence of
species that preserves biological diversity in the face of the inexorable
forces of natural selection. 

That said, domestic animals don't follow the rules, because they are not
subject to Natural Selection.  Instead, they follow the rules of Selective
Breeding.  These are our rules, not nature's. 

-- 
Joseph Morlan, Pacifica, CA 94044  jmorlan (at) ccsf.edu 
Birding Classes start Feb 7 in SF  http://fog.ccsf.edu/~jmorlan/
California Bird Records Committee  http://www.wfo-cbrc.org/cbrc/