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In a message dated 95-12-01 02:12:16 EST, ornstn@inforamp.net (Ronald
Orenstein) writes:

>I must confess I doubt this.  The statement is true for fully evolved
>powered flight - but for any intermediate stage I can imagine any sort of
>flapping semi-flight would be a lot more energetically costly, and probably
>less effective, than a gliding mechanism (and we DO have intermediate stages
>in the evolution of gliders, from Costa Rican frogs that can use the webbing
>of their feet to slightly alter the course of their fall, through the more
>spectacular Asian "Flying" frogs, right up to the giant flying squirrels and
>colugo that can glide for hundreds of metres).
>To me the only locomotor advantage for an arboreal animal of powered flight
>over gliding that I can imagine intermediate stages for are leaps UPWARD
>from branch to branch or moving among branches in close quarters where
>gliding would be useless but a fluttering semi-flight might be quite handy.

I would guess that any intermediate stages between gliding and fully powered
flight would not be characterized by useless random fluttering. Indeed, your
second sentence may have answered the questions in your first sentence.

The problem is not with the evolution of flight, it is with our present
inability to imagine the stages in which this evolution took place.