Re: Metamorphosis - plausible evolutionary scenario?

On Nov 18, 2:09 am, pineapple.l...@xxxxxxxxx wrote:
On Nov 17, 3:20 am, Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:

The "transform its body into a gelatinous
mass" step was not a first step, but an end-product.

Could you explain?

No doubt the ancestors of butterflies did not undergo such a
radical transformation - and could not fly. They probably
just grew legs and genitals: fairly orthodox developmental
steps that do not involve self-liquefaction.

If my memory of biology serves me correctly, the butterfly is not
simply a caterpillar with wings, legs, genitals, etc. It is an
entirely new, different creature built "from scratch." You could
essentially consider it a whole new species, a whole new animal. >If this is correct, explain the above comments in light of this?

Yes, Stephen Gould fooled me too. However, the caterpillar isn't
totally destroyed in the transformation to butterfly. Gould says that
it is, but it turns out that he exaggerated. The metamorphosis in the
cocoon isn't quite a complete meltdown. Sure, the caterpillar grows a
new set of legs, antennae, etc. However, this happens to every insect
every time it molts.
That is what I believe is the accepted route to metamorphosis in
insects. It is molting and regeneration after molting. The
regeneration part is partially delayed in insects that undergo
metamorphosis, relative to insects that don't. The development of the
embryo is delayed, although its growth is not delayed. So a form
vaguely similar of an insects embryo becomes the larva. A larva is an
overgrown, rather large embryo. I think this sort of thing is called
neotony, but someone else could correct me on this.
For example, the caterpillar has six true legs, just like the
butterfly. The caterpillar has three sections that can be barely
recognized as head, thorax, and abdomen. Eaction of these three
segments are themselves broken up into segments, that don't join
completely until after the metamorphosis. So the caterpillar really is
a rather ugly caterpillar. However, that is the state in embryos even
in insects that don't undergo metamorphosis.
I got some of this from Richard Dawkins book, "Climbing Mount
Improbable." He didn't explain metamorphosis, but he describes the
anatomy of caterpillars much better than Gould did.
I usually like Gould, by the way. However, I have learned to check
everything he says. Twice.

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