Re: Plausible evolutionary scenario for metamorphosis?

On Thu, 15 Nov 2007 17:43:29 -0800 (PST), Friar Broccoli
<EliasRK@xxxxxxxxx> wrote:

On Nov 15, 1:22 pm, pineapple.l...@xxxxxxxxx wrote:
test

Plausible evolutionary scenario for metamorphosis?

This is a subject I know nothing about, but the question seems
to have an obvious answer: The larval stage is just a mobile
egg.

At some time in evolutionary history some animal hatched
from a soft egg, possibly one that was laid in rich organic soil.

Initially the egg absorbed extra nutrients directly through the
membrane of the egg. Gradually this evolved into a simple mouth
with an ability to wiggle a bit to get around, like a worm.
Some of these worms went even further to develop legs to become
efficient foragers.

This is a wild guess, but seems plausible to me.


Sorry, it is definitely a wild guess but seems totally implausible to
me.

Metamorphosis is an ancient and very widespread phenomenon and is
really just an extension of stages of development past the embryonic
state into the free-living form. Plants have alternate life stages,
although these include both haploid and diploid states. It is very
common for particular organs, especially reproductive organs, to
appear at a different time than, say, the 'vegatative' organs
necessary to sustain life: leaves and roots in plants, digestive
systems in animals. Moss plants grow from a filamentous protonema
form; jellyfish go through a planula larval stage then a stationary
(sessile) polyp form before the free-floating medusa form appears.
Roundworms and flatworms and molluscs and arthropods and echinoderms
and chordates all show multiple life stages.

Building a specialized organism is a very tricky and difficult
process. Building it in stages, each of which is capable in different
ways to different degrees of solving the problems of living seems to
be the basic plan. It is not easy to acquire the necessary materials
to build a body and provide the energy to do so while at the same time
trying to escape predation all during the time when the body building
is still incomplete.

.

Relevant Pages

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