Re: Speciation question

On Mon, 29 Aug 2005 07:00:29 -0500, Chris076@xxxxxxxxx (C.L.) wrote:

>
>Can someone please tell me if this statement is true? (From Science on
>Trial, by Douglas J. Futuyma - 1982, pp. 23-43). I've read parts of The
>Origin of Species but don't own a copy:
>
> [ The first five chapters of the Origin lay out the theory that
>Darwin had conceived. He shows that both domesticated and wild species
>are variable, that much of that variation is hereditary, and that
>breeders, by conscious selection of desirable varieties, can develop
>breeds of pigeons, dogs, and other forms that are more different from
>each other than species or even families of wild animals and plants are
>from each other.]
>
> What breeds of animals (dogs, pigeons, etc.) are more different from
>each other than species or families of wild animals and plants from each
>other? Since some of Darwin's ideas are no longer considered valid
>today, was this one of them? Is this a true statement or just
>misleading? If true, what definition of "species" are you using?
>(Animals, plants, insects, that can even appear identical but that
>cannot breed with other species of the same genus? - that doesn't sound
>very "different".) In other words are the dogs still dogs, pigeons still
>pigeons?

(Oops, I accidentally sent this off prematurely, without finishing)

I accept your statement that you are here to learn and what a simple
answer to a simple question.

The usual examples of dog differences compares Great Danes with
Chihuahuas. These two breeds of dogs differ tremendously in size,
behavior, and appearance. They are easily and immediately recognized
as different. Two "sister species" of fruit flies can't be told apart
except by experts. Some of Darwin's famous finches are so similar
that it requires careful examination and measurements to distinguish
them -- even Darwin did not recognize that they were different until
ornithologists back in England (who, of course, were creationists as
was everybody at the time) where he sent his specimens told him. The
many varieties of sparrow or warbler flitting through our forests and
fields look very similar until you learn the fine details. And can
you tell the difference between all the varieties of Caddis Fly? But
any trip to a dog show will reveal a large variety of easily
distinguished breeds. The English of Darwin's time were famous for
breeding pigeons of very unusual and fanciful plumage all of which
look very different. And goldfish breeding is very popular. Just
google on these and you will see pictures showing how vastly different
the breed appear.

The problem this raises is the difference between superficial
differences that may be very apparent but insignificant biologically
and significant differences that may be very subtle but that represent
very important factors, indeed. In modern biology, that is for the
last fifty or more years, the "biological definition" of species has
been used to sort out just which differences are really significant in
evolution. If two organisms cannot interbreed, their genes do not
belong to a common gene pool, hence they belong to different species.
Some people claim that a great dane could not breed with a chihuahua
and so perhaps could be considered different species but it is easy to
breed a whole variety of intermediates -- a chihuahua with another
small dog and a great dane with another large one, generating a series
of hybrids all of which would eventually look quite similar and freely
interbreed. In that way the great dane genes and the chihuahua genes
would freely interchange in the common dog gene pool and so they must
be in one species.

Yes, dogs are still dogs and pigeons are still pigeons, but insects
that look almost identical with very different mating behavior and
copulatory organs that don't mesh properly are different species.
Species are sets of populations that generally freely interbreed
among themselves and generally do not breed with others. That is,
species are separate gene pools.



.

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