Richard Hall hall at
Wed Sep 16 13:46:06 EDT 1998

John Grehan wrote:

> I don't think history has to be necessarily less scientific,

Sure it does.  History can not be repeated nor directly observed.

> 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.

Empirical basis:

1. Extant mayflies, and many other insects as well, form mating swarms.
2. Insects and arthropods of all sorts are heavily exploited food
3. Numerous studies have demonstrated the validity of sexual selection,
or a correlation between the possession of some trait and mating
4. Dispersal is a fundamental trait of anything that grows, reproduces,
and consumes.

Unless you want to assume that the past was radically different from the
present, then it is fair to extrapolate these empirical facts backwards
in time.  Truly, we should assume time invariance unless we have reason
to think otherwise.  The fossil evidence from the time of insect
emergence strongly suggests that the stage was the same as it is today,
with only the players being different.

Do you have any reason to think that the planet was radically different
back then?  That is a huge supposition, and I would need a whole lot of

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

I don't understand this sentence.

> >> 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).

I'm having a hard time understanding this objection.  I think that your
understanding of natural selection is different than mine, so I will try
to explain mine briefly.  Forget the phrase "survival of the fittest",
please, everyone: never utter it again.  Natural selection is a positive
force better described by the phrase "persistence of the fecund".  It
deals with reproductive success, with death or failure to mate being
merely the null case of zero reproductive success.  Natural selection
says that existence will follow the vector of maximum reproductive

The gilled members were not wiped out.  They are the larval stage. 
Wings evolved in the adult, reproductive stage, but they are made of the
same genes as those which make gills.  Are you familiar with the term
"serial homology"?  "gene duplication"?  Most certainly there was a gene
duplication involved, either duplicating one or more gill structure
genes or one or more regulatory genes which influence gill structure
(the specifics of which genes is experimentally accessible, but if the
experiments have been done, I don't know the outcome).  After
duplication, the abdominal gills could continue to be developed as they
always had, and the expression of thoracic gills could evolve
independently.  Duplication may not involve a single gene, though it is
a single mutation.

Once the abdominal and thoracic gills became independent by virtue of
this duplication mutation, you essentially have a new structure, not yet
a wing, but a protowing.  It didn't have to become a wing at this point,
but it did, and flight did evolve.

> > Were the insects necessarily "invaders"?

OK, let's just say that they colonized a new environment, specifically
an aquatic environment which was less oxygenated and less saline.  I'm
not sure why it matters whether this colonization was passive or active.

I'd be happy to continue this discussion if you are finding it fruitful
and not frustrating, but we might want to slip out of this newsgroup and
into email or  Is the lepidopterist audience tiring
of this thread?

Rikki Hall

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