Re: Blind scorpions (or fish) as proof of evolution?

>
> The metamorphosis of a caterpillar into a butterfly is something that
> causes me to question the feasibility of evolution.
>
Much of the rest of the post has been addressed, so I'll try this one. I
don't know full details of what is known about insect metamorphosis, since
my area of focus is mollusks, but there are certainly some hints of how it
would come about found by looking at other insects. (There also are
probably some ideas relating to the vast amount of data we have on fruit fly
development and genetics; however, to be really useful on this question they
need to sample a bit farther afield and get similar intensive data for some
insects with simpler metamorphosis).

Insects and other arthropods are part of a vast group of phyla that
regularly molt their outer layer. Often there is some degree of change in
appearance between molts, though rarely as drastic as seen in the
holometabolous insects with their larva-pupa-adult sequence. (Some
parasitic crustaceans, notably some barnacles, go through drastic changes,
but these would often qualify as degeneration). Such molting provides a
simple way to have a relatively durable outer layer, yet still be able to
replace it since it gets a lot of wear and tear and gets tight as one
grows.

Among the most primitive living insects are the silverfish. You may have
seen and squashed one as it ran out of a pile of old papers or books. They
have no wings. Adults are just bigger versions of the juveniles. The egg
hatches into a small silverfish, and they just get bigger with each molt.

Then there are several kinds of insects that have some distinctive features
as adults, but have fairly similar looking larvae. In particular, the adult
stage has wings and the larval stages don't. (Mayflies have wings in the
last larval stage as well-they are the only insects to do this. A few
of species at this level and other, more advanced insects, have lost the
wings in the adult stage.) Examples include dragonflies, grasshoppers,
cockroaches, and true bugs. In some of these, the larvae lead somewhat to
very different lives from the adult. For example, several insects have an
aquatic larva and flying adult. This means that larvae and adults are not
competing with each other and lets the adults disperse to find mates and new
places to lay eggs while the larvae can stay in a good place to get food.

Finally, there are the holometabolous orders of insects that have a pupa
stage in between a larva and the adult, which are usually quite different
from each other. Flies, fleas, bees, beetles, and butterflies are
examples. The pupa provides a relatively secure case in which to undergo
the substantial rearrangement from the larval eating machine to the adult
dispersing and reproducing (and often eating something different, if
anything) machine.

It does seem as though this particular innovation happened only once.

Assuming that God planned it all from the beginning and designed the
universe such that star A in galaxy B would reach supernova stage at time X
and emit cosmic ray C to arrive on earth at time Y and hit gonadal DNA in
primitive insect D, causing mutation E does help address the complain that
it seems improbable, but it is an assumption outside the reach of the
scientific data.

> --
> Dr. David Campbell
> 425 Scientific Collections
> University of Alabama
> "I think of my happy condition, surrounded by acres of clams"
>
Received on Mon Jun 5 12:56:38 2006