>But, all in all, you have confirmed my contention: that
though they cannot provide a general definition of "species"
or "speciation," evolutionists know it when they see it.<
Recognition of species is not confined to evolutionists, and
even many antievolutionists allow some speciation as
"microevolution". There is general agreement that a
barrier to reproduction is a component of the development
of new species; the problem is deciding what is legitimate
evidence of the barrier and how solid a barrier must be.
Thus, I doubt that any evolutionary biologist would deny that
the apple and hawthorn flies are in the process of
speciation. However, there would be a lot of debate as to
how close they are to becoming two species and what
would be conclusive proof that they had speciated.
For asexually reproducing forms, some simply assert that
species do not really apply; others try to use some criterion
of differentiation. It is especially tricky to apply to the many
organisms in which asexual reproduction prevails, in some
cases so much so that sexual reproduction was only
recently discovered, yet occasionally sexual reproduction
does occur.
>Yet they are quick to hang creationists out to dry when
such an approach is used to define "kinds."<
I do not object to "kinds" simply because they do not get a
fixed definition. I do have a problem with creationist
attempts to define kinds as a firm, fixed category.
Uncertainty in evolutionary definitions does not make the
Biblical category any less (or more) nebulous. I am also
dubious of attempts to take the passing Biblical references
to kinds and make them into an absolute barrier that divine
inspiration has shown to be impassible by evolution.
Finally, in identifying fixed kinds, antievolutionists typically
pick forms or levels for which good transitional forms are
known. Claiming that there is no evidence for continuity
between X and Y when there is is irresponsible.
As the debate over species definition is a current
significant issue in biology, knowledgeable evolutionists
will not claim that the definition of species is fixed in stone.
The unambiguous examples of the production of new
species are the hybrids; others are certainly undergoing a
process that would eventually result in the production of
new species, but drawing the line is not so easy.
It may be helpful to note that evolution provides a strong
incentive for reproductive barriers to develop between
populations with different specializations. If mixed
offspring typically do poorly in competition with either
pureblooded population, then parents that mate with
individuals from the other population are wasting their effort
relative to those that mate with more similar individuals.
For example, a hybrid between the apple fly populations
and the hawthorn fly population might head for a hawthorn
bush when apples are ripe, thus being in the wrong place
for an apple mate and the wrong time for a hawthorn mate.
The reproductive effort of the parents is thus wasted,
whereas mating with an individual preferring the same fruit
would have led to a fine crop of grandmaggots. Thus, any
fly that gets better at rejecting potential mates that go for the
other fruit will be more succesful. Thus, they may be
expected to develop total barriers to reproduction, though
they do not have them yet.
>>* I have not seen the new varieties of bacteria called
species.<<
>But have you seen the their creation cited as a proof of
"the theory of evolution"? If new species are not being
created, then how is the theory being confirmed?<
Novel genetic features and new information are being
created without intelligent design. Variation is developing
in a population and change occurs as a result of selective
pressures. Darwin spent an inordinate amount of time in
the Origin of Species talking about pigeon breeding, not
because he thought new species were being created but
because distinctive varieties were appearing and being
selected for.
>>A horse and donkey can be crossed to produce a mule,
but the mule is almost always sterile.<<
>Had anyone suggested that the caballus and the asinus
were not of different species? <
If two forms must never ever ever ever interbreed to be
separate species, than they are disqualified. They are
well-separated, but interbreeding is not a total
impossibility.
>BTW, has any reputable biologists (lately) crossed
politically correct barriers, and implied that human
populations of different races may be of different species?
Surely, when considering, at least historically,
morphological differences and geographic and social
barriers prohibiting "intermarriage," and the various
definitions of "species" which you have proposed, this
conclusion must be the "elephant in the parlor," that
everyone sees, but no one will mention. <
Some versions of the not out of Africa idea could be used to
recognize modern humans as multiple species. This idea
has very low support, in light of the molecular evidence for
extensive genetic input out of Africa into the modern
populations. (Glenn's view, that this out of Africa
component did not entirely replace the existing
populations, is compatible with the molecular evidence but
also promotes recognizing more past humans as
conspecific rather than splitting modern humans. The
extreme out of Africa view is that the latest migrants out of
Africa totally replaced the prior populations of Europe, Asia,
and Australia; some of these were then the first to reach
the Americas.). A recent popular science book on the
history of Australia seems to claim that the Tasmanians
might have been surviving Homo erectus, but I have not
seen a more credible source to support that. However, the
mobility of humans has generally maintained a high level
of interbreeding between adjacent groups. I also saw a
creationist book in the late 1980's that was making such an
argument, claiming that Lapps and Ainu might be
Neanderthals and not conspecific.
>Of course, I would not subscribe to such a concept, but,
then again, I am not sure I agree with several of your
suggested definitions of "species."<
As there is not agreement among biologists on defining
species, you certainly do not have to agree either.
However, be aware that someone using a different
definition will recognize speciation differently.
Dr. David Campbell
Old Seashells
46860 Hilton Dr #1113
Lexington Park MD 20653 USA
bivalve@mail.davidson.alumlink.com
That is Uncle Joe, taken in the masonic regalia of a Grand
Exalted Periwinkle of the Mystic Order of Whelks-P.G.
Wodehouse, Romance at Droigate Spa
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