Wings

[John Grehan]

More discussion comment in response to Rikki Hall


>I don't think that the cause is particularly crucial to the hypothesis
>that wings evolved from gills; after all, that is more historical than
>scientific. 

I don't think history has to be necessarily less scientific, but in this
case I would agree as the particular causes invoked here are pure
speculation without any empirical basis that I am aware of. Primarily,
the invokation of predation pressures is simply an extrapolation of
selection as it is observed in the present.

 It's nice to have a sensible, complete story to go along
>with the hard evidence of homology and fossil evidence, but a notion of
>why the change occurred is merely historical and difficult or impossible
>to prove.  We should simply prefer the story which invokes the fewest
>and most commonplace assumptions about the protoinsects' environment. 
>If you don't like to invoke predation pressure, choose another story. 

I would not chose any "story" of the kind invoking selection events
as described above as I have no empirical basis to select.


>> Aside from its value as a predator-avoidance mechanism,
>> >flight may have also allowed these early insects to disperse upstream
>> >more easily than they could have in the water.

I agree, but that would be a consequence of having flight ability, not a
cause of the ability.


>> 
>> But they managed ok before they had wings.
>
>They sure did.  That doesn't mean they couldn't improve though.

The improvement (flight) could only come about after the new structure
(wings) had
evolved, so it couldn't be selected for before hand (perhaps unless you are
suggesting
that there was a population of aquatic gill breathing insects which also
happened to include individuals that had functional wings and were also
terrestrial, and then the gilled members were wiped out (selected out). In
which case I would assume (correct me) the gill-wing transformation would
have to be a single gene difference to represent a random variation which
was also correlated with individuals "deciding" (for the lack of a better
word) to go on to land. None of this seems at all "sensible" (not that
nature has to be sensible).

> Were the insects necessarily "invaders"?
>Well, at some point, yes, but again, that is historical speculation. 

An alternative was that they were passively introduced into the new
environments. Rather than individuals physically moving in as invaders,
they might find themselves stranded as the ecology and structure of the
environment changed.


 We
>do have fossil evidence of swamps without insects followed by swamps
>with insects, so that suggests an invasion.

We do not if by invasion you refer to individual insects moving from one
environment to another.

  Invasion of new niches is
>also known to precipitate adaptive radiations, which rapidly produce a
>diversity of forms.  

Again I don't agree. All we have is evidence of insects entering new niches
(I don't think one can enter a niche since niche referes to ecological
relations). Whether they invaded or not is another matter. Entering new
habitats and estabishing new niches
might

>Rikki Hall
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