Wings

[Mark Walker]

Rikki Hall has posted a fascinating account of Brodsky's hypothesis on
insect wing evolution, and I must admit that it was interesting reading.  I
don't think it provides any insight as to why or how the ancestors would
have evolved down the metamorphosis path to get there.  There just seem to
me to be too many intermediate steps that would have had to fall into place
for this to be convincing.  I know, I know, with millions and billions of
trials you can come up with Shakespeare.  However, as far as the age of the
earth is concerned (and the relative intelligence of someone speculating on
it), it seems to me that the NEED for this many permutations is the prime
mover for the number of zeros attached.  Since the inception of evolutionary
theory, the "universally" accepted predicted age of the earth has
mysteriously been tracking the numbers associated with an increased
understanding of stochastic processes.

Anyway, I will cease my argument for now, only because I do agree that the
debate is an old one, and not entirely appropriate in this forum.  On the
other hand, I believe it perfectly scientific to raise the question and "not
roll over and play dead".  Majority consent never was sufficient
justification to cease from questioning the world view.  

Obviously, I am motivated by more than science.  It would be unscientific,
however, to discount my perceptions solely on this association.  I am not
now, nor have I ever been associated with a "Creationist Party" (heck, I
didn't even attend my 20th high school reunion), but I am thankful for the
learned research and acquisition of experimental data that comes from this
camp of revolutionaries (images of Woodstock not withstanding).

Oh, and for the record - I haven't as much as caught a butterfly for over
three weeks.  Bummer.

Mark Walker.

> -----Original Message-----
> From:	Richard Hall [SMTP:hall at charon.ns.utk.edu]
> Sent:	Thursday, September 10, 1998 2:36 PM
> To:	leps-l at lists.yale.edu
> Subject:	Re: Wings
> 
> There is an excellent book out called the Evolution of Flight in
> Insects, by Andrei Brodsky.  Brodsky discusses the aerodynamics of
> flapping flight and comparative studies of wings and comes to the
> sensible conclusion that wings evolved from the gills of aquatic
> insects.  I'll try to explain the evidence as briefly as I can.
> 
> The primitive protoinsect most closely resembled extant Mayflies,
> Ephemeroptera, and was an aquatic critter with externalized gills on its
> abominal and probably thoracic segments too.  These gills had a
> musculature associated with them which allowed the organism to move them
> through the water, enhancing oxygen absorption.  This allowed the
> organism to invade oxygen-poor habitats such as marshes and swamps,
> where the first insect appears to have evolved.  The protoinsect was
> probably marine or tidal and shrimp-like.  Many larval Mayflies retain
> shrimp-like characters, including locomotion by tail-flipping.
> 
> The invasion of brackish marshes probably continued into freshwater and
> inland into rivers and streams.  The protoinsect likely had swarming,
> short-lived reproductive forms as do extant Mayflies, wherein
> individuals essentially exerted all of their energy to enter a swarm and
> copulate, dying shortly therafter.  This placed a premium on motility,
> and gills expressed on the thoracic segments, where musculature was
> already stronger and better developed, became increasingly useful as
> swimming organs.  Predation pressure probably drove these mating swarms
> out of the water, where thoracic gill flapping became weak flight became
> strong flight.  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.  Similarly, during the
> invasion of stagnant waters, the protoinsect would become more dependent
> on crawling or swimming to get around, whereas its predecessors might
> have relied on tides and currents to get around.
> 
> That's the basic story as I understand it.  There is solid evidence to
> back this story up:
> 
> 1.  There is extensive homology between gills and wings, including
> venation patterns and muscle attachment sites.  Kukolova-Peck has
> exhaustively demonstrated this during her career, and Brodsky reviews
> her findings in his book.
> 
> 2.  The aerodynamics of flight is such that gliding is more difficult to
> achieve than powered flight (flapping), and phylogenetic analysis shows
> that gliding has evolved from flapping on numerous occassions, whereas
> flapping seems to have evolved once and is the primitive state.  Brodsky
> provides mathematical and experimental support for this point.
> 
> 3.  The fossil record is consistent with wings evolving in an aquatic
> insect in a swamp, as the oldest insect fossils are Mayflies found
> amidst other swamp dwellers.
> 
> 4.  Water being more bouyant than air, it would be easier to evolve
> flight in water, develop strength, and then conquer the air.
> 
> This scenario is vastly superior to the standard tale which still runs
> on a video screen in the Ortho Insect Zoo in the Smithsonian and which
> is still taught in entomology classes by the majority of entomologists
> who haven't kept up to date.  The standard tale is that a jumping insect
> like a grasshopper evolved flattened protrusions from its thorax which
> either allowed it to glide farther on jumps or to thermoregulate its
> body.  Somehow theses protrusions developed musculature, and presto!
> wings.  The magical evolution of musculature is unexplained in this
> scenario, and it is inconsistent with phylogeny and the fossil record
> anyway.
> 
> It is curious that several of the oldest bird fossils are aquatic and
> that the extant form considered most primitive is the Loon, an aquatic
> diver.  I think that it is only a matter of time before ornithologists
> adopt a similar tale to explain the evolution of flight in birds, with
> wings evolving as diving/swimming organs before becoming capable of
> aerial flight.
> 
> Spread the word, entomologists, and check out Brodsky's book.
> 
> Rikki Hall
> (remove "deleteme." from email address)