Re: define species was Re: Modern Neanderthals?

Susan S. Chin (susansf@netcom.com)
Tue, 29 Oct 1996 00:01:16 GMT

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: >Lorenzo L. Love wrote:
: >>
: >> "David \"Oso\" Sierra" <dsierra@lonestar.jpl.utsa.edu> wrote:
: >>>If two groups can successfully interbreed, dispite their
: >> >physilogical differences then they are, by defintion, part of the same
: >> >species.
: >>
: >> Like Canis familiaris, Canis lupus and Canis latrans? Dogs, wolfs and
: >> coyotes in any combination can produce fertile offspring, therefore
: >> they must be all the same species. Does that means the entire
: >> classification system is faulty?
: >
: >No, just that the definition of "species" is not very well-defined.

There may be an explanation for this difficulty in coming up with a
good and universally agreed upon definition of species.

I haven't read much of the current literature on this, but this topic
was one of huge debate among historians of science, philosophers, and
interested evolutionary biologists about 10 years ago.

The gist of their argument is that the reason it is so difficult to pin
down one definition that can be used in all instances when referring to the
biological unit "species," as used in genetics, evolutionary biology,
paleontology, etc. is that in these disciplines, one only has access to
one aspect of a species. This argument gets really more into the
philosophical realm, so I won't attempt to go any further on this. But
the argument as I recall it is that species are "individuals" in the
sense of "one coherent biological unit" with interbreeding capability at
the center of it. Rather than defining as one species any two organisms
with the ability to interbreed, producing viable offspring, other
criteria have to be established, including behavioral, ecological,
morphological, physiological, depending on what aspect of a species
one's study involves.

Using the dog example above, with some help in the laboratory,
dogs observably morphologically distinct such as a chihuahua and
the Saint Bernard can still produce fertile offspring (according to the
earlier post). So what does this all mean? Not much since dogs are
artificially manipulated and bred by humans. Calling them breeds
pretty much solves the problem.

As far as the whole species definition goes, it really depends on what
you have to work with. I know this sounds obvious on an intuitive level,
but this entire topic of species has always been one of those that seems
really simple, until you're confronted with the task of defining or
defending what you've considered a population that represents one species
or two. Or, as someone pointed out, maybe it's a generic level difference.

The point being that what we've traditionally considered defining
properties of species are merely characteristics of a biological entity.
These characteristics vary depending on the level of biological time and
organization you are studying, whether at the molecular, genetic,
cellular, organismal, populational, geographical, or species level
(and between and beyond).

And of course, this all sounds good and operational, but in fact, it's
much more complex in reality. That's what makes it so much fun...

Susan

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                                             susansf@netcom.com