"Willi" wrote in message
...


Jonathan Cook wrote:

rw wrote in message
...

On 2004-02-06 15:21:48 -0700, (Jonathan Cook) said:


Lions and tigers have been bred and produced fertile offspring. Would
you
call them one species?


Assuming fertile offspring is the norm between the two, yes.

If biologists were consistent in applying their own "rules" about
what constitutes a species, such as physical, geographic, or
behavioral isolation, then we ought to have a multitude of human
species, and a multitude of dog species, and plenty of other
examples. The current use of these rules is "soft science" and
it bothers me.

Lately it seems like the readiness to declare new species is also
founded on political reasons -- mainly to bring the endangered
species act into play and "preserve" the environment. In NM we have
the Rio Grande silvery minnow, a very endangered species. Well we
had a state biologist talk at our FF club and I learned that there's
a Pecos river silvery minnow that is not endangered and that can
only be distinguished from the RG minnow by a delicate autopsy
and inspection of the vertabrae at the base of the skull. When I
asked why it is considered a different species, I was basically
talked down to as if I didn't understand science and no
reasonable person would even think that (they *are* geographically
isolated and have been for a while).


I used to accept your definition because it seemed to make the most
sense and seemed concrete and absolute. However, through reading and
thinking about it, I've come to the conclusion that it is as arbitrary
as any other definition. There are problems with any definition of a
species. Any definition of "species" is just an attempt to choose a
specific point on a continuum.

Although your definition may seem concrete on the surface, it too is
arbitrary and depends on your definition of "bred" and "fertile" and
when man's intervention is thrown into the mix, things get even more
complex.

With your definition, some of the choices that need to be made include:


Animals that will occasionally breed naturally in the wild

Animals that would breed naturally in the wild but never come into
contact because of physical barriers

Animals that could breed naturally in the wild but don't because of
behavioral differences

Animals that will breed only when confined together in captivity who in
the wild have contact but choose not to interact

Animals that will breed in captivity only when treated with hormones or
other types of manipulation

Animals that won't breed but will have fertile offspring through simple
artificial insemination

Animals that won't breed but will have fertile offspring through
artificial insemination with physical changes made such as a change in PH

Then we get into genetic manipulation

As man makes more technological advances, more and more levels will be
introduced that will need to be considered.

How the definition is to be used adds even more complexity. Is it being
used to describe the evolutionary process, explain genetic differences,
for political reason, etc.

Plants......you forgot about plants. How about an apple trunk grafted onto
pear rootstock and later augmented with plum and cherry branches? (It's
doable.....they're all Rosaceae and graft relatively easily.)

And then, there is the rather knotty problem of asexual reproduction. Any
definition that depends on the successful mating of a pair of individuals
resulting in fertile offspring sort of leaves yeasts, for example, out in
limbo. If no two of the saccharomyces cavorting in my bread dough ever get
together to do the nasty, is every one of them a different species?

And what about bacteria that simply grab a chunk of DNA from some host and
make it their own? Looks to me like any one of them may actually be two or
more species based on genetic evidence.

Any recognized species of lichen IS two species, and of different kingdoms
at that.

Viruses. Viruses don't have ANY DNA of their own.

Species are a fiction. They can be very useful fictions, but the uses to
which they are put are not always noble or even justifiable.

The vast majority of species on the planet fail to conform nicely to the
traditionally accepted definition.

Wolfgang
mitochondria, anyone?