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Re: bauplan convergence



In a message dated 6/8/00 3:15:51 PM EST, twilliams_alpha@hotmail.com writes:

<< If insects could evolve flight from the ground up (or the pond up), why 
not 
 vertebrates? >>

Insects are by and large >far< more lightweight than even the smallest 
lizards, and they can be easily blown aloft by even a light wind or breeze. 
It would be quite advantageous for an insect to develop flight surfaces for 
directional control in such circumstances. (Wonder why there are no flying 
spiders. Maybe the insects beat them to it?) On the other hand, it takes 
quite a strong gale to lift a lizard or other small vertebrate off the ground 
and carry it off (this does happen every so often)--not the kind of wind that 
occurs regularly and steadily in any conceivable environment on earth, and 
consequently not a regular enough environmental feature that would foster 
evolution of flight control surfaces. In the case of insects before wings 
evolved, the energy required to remain aloft was provided by air movement; in 
the case of vertebrates, the energy required to remain aloft was initially 
provided by gravity: the flight surfaces evolved to control falling and to 
turn falls into controlled glides. Such flight surfaces have evolved 
repeatedly in arboreal vertebrates, from "flying frogs" and "flying snakes" 
to gliding lizards and flying squirrels, and there's no reason to believe 
they would not also have evolved in small, arboreal Permian archosaurs. 
Feathers, for whatever reason they originally appeared, are a natural source 
of flight surfaces for arboreal gliding vertebrates.