Re: No Such Thing As "Macro" Evolution

r norman wrote:

> On Mon, 21 Nov 2005 08:23:16 -0700, dkomo <dkomo871@xxxxxxxxxxx>
> wrote:
>
>
>>John Wilkins wrote:
>>
>>
>>>Dale wrote:
>>>
>>>
>>>>I guess many people in this ng already know this, but it's really coming
>>>>home to me that there is no such thing as "macro" evolution, it's all the
>>>>same thing, there's no difference, there's just evolution. So let's see if I
>>>>understand this correctly.
>>>>
>>>>The idea of species itself is just a human construct, a model of reality to
>>>>help us think about and categorize living things. The model breaks down
>>>>sometimes, there seem to be species that can interbreed because they are
>>>>closely related, so people aren't sure whether to call them separate species
>>>>or not.
>>>>
>>>
>>>
>>>"Species" as a category is not a human construct. The organisms *themselves*
>>>"recognise" species.
>>
>>What about bacteria and viruses? What about all the plants and animals
>>that don't reproduce sexually? I don't think these spend much effort
>>"recognising" themselves for breeding purposes. It seems to me that the
>>most general definition of species must be taxonomic, and that would
>>make the "species" concept in large part a human construct.
>
>
> Asexual reproduction is a completely different story. And viruses
> are out of the picture, not ordinarily being considered "organisms".
>

In the case of viruses perhaps "quasi-species" is a better term.
Consider the HIV virus. Being an RNA virus, it mutates like crazy. Yet
we consider the various strains of HIV as still being "HIV". What
classification system are we using here? If the bird flu virus mutates
so that it can be transmitted between humans, we'll still call it bird
flu, although it'll be a separate strain. Perhaps that's because its
symptoms will be similar to its cousin bird-to-human strain.

In the case of prokaryotes, there are nevertheless distinct species. E.
coli, for example. There may many different "strains" of E. coli but
somehow we consider this class of bacteria as being a species. Then
there are those HELA cells dividing in laboratories all over the world.
HELA is considered its own species (I know, I found this very
surprising when I first learned of it).

> However the fact is that very few (comparatively) plants and animals
> reproduce asexually.

I don't have time to look up examples, but I'm pretty sure dandelions
reproduce asexually. So how can dandelions be classified as a plant
speicies if not morphologically and behaviorally (by which I mean
developmentally)?


--dkomo@xxxxxxxx


I think you are thinking of plants and animals
> that do not have sexual intercourse.There are ways of "recognition"
> that don't involve behavior. An underappreciated reproductive
> isolating mechanism is gametic incompatibility -- the sperm of one
> species simply does not recognize the signals produced by the egg of
> another species and so fertilization is not possible. This applies to
> virtually all species of algae and animals that simply release their
> gametes into the water. There are also usually environmental or
> chemical cues to synchronize the release of gametes by all members of
> one species at a time different from that used by other species. In
> the case of seed plants, there are chemical recognition factors
> between the pollen grain and the cone or stigma of the recipient to
> stimulate or inhibit the development of the pollen tube and make
> fertilization impossible between species. Of course there are also
> environmental cues to synchronize the development of cones and flowers
> and animal pollinators do distinguish species of plants that they
> visit.
>
> Then there are the multitudes of sexually reproducing fungi and
> protists. Frankly, I don't really know how they manage but they, too,
> have ways of differentiating between "kinds".
>
>
>
>

.

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