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Re: Digit Loss (kiwis and tyrannosaurs)



I wrote:

<<A positive effect can even be selected against.>>

Dan Bensen (dbensen@gotnet.net) wrote:

<If the effect is positive, by definition, it is selected for. 
Features selected against are negative, even if they have
potential for being positive.>

  Here we are arguing two different things. Should I have my
little monkey make three consecutive changes to the car, and the
first three are beneficial, and the third makes it explode,
these are just effects. Only the third has a negative effect.
Each has been selected for. Selective pressure and the effect of
the mutation pressure are two different things. Having an
abnormally small appendix prone to causing lethal effects to the
organism isn't making it keep disappear, but it's still there.
The appendix is an example of having a negative effect that is
being selected for. If an organism has a positive effect, and
this does not benefit the population and does not propogate
through the population, it is not being selected for. Perhaps a
better example is in the offing...

<No matter how much you want some specific adjustment to your
car (for instance, you might want nitros added in), that
adjustment will _never_ appear unless chance directs the monkey
to make the appropriate modifications.>

  Did I not say that nature is not sentient? There's nothing
that drives a mutation. It occurs. You can't inherit some
ancestors accidentally cut-away nails and get claws from hooves
... some may not like it, but chance it is.

<Not that I'm trying to get the last word or anything, but it
seems that our argument is getting bogged down by particulars,
so we should probably end this thread.>

  The point of evolutionary theory is particulars. There are no
generalities :) 

<There is no trend towards larger size in horses, but since
horses began near the minimum horse [=perissodactyl, as
*Hyracotherium* is very similar to the form of the common
ancestor of horses, tapirs, and rhinos, and has even been
suggested as _it_] size, a randomly diverse speciation of these
animals produced animals larger than the precursers.>

  If one takes the basal horse lineage, and goes from the Eocene
up to the Holocene, one sees that later lineages are bigger than
their predescesors. This is what is called a "trend."

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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