Samantha asks:

>how did animals ever evolve lungs? i mean, gills worked perfectly well
>for water-bourne creatures. why would lungs spontaneously pop up?
>before land-bound creatures existed, what would be the evolutionary
>advantage of developing these superfluous organs?

There's nothing "superfluous" about lungs. They are the co-opted
swim bladders
of an earlier architectural design in fish, now evolved for use in a different
environment than they were originally intended, but close enough initially to
serve a different purpose -- and confer significant evolutionary advantage in
an otherwise empty competitive adaptive zone, even if quite imperfectly
accomplished in the beginning.

For more information on the evolution of lungs, please see:

     http://www.ucmp.berkeley.edu/vertebrates/sarco/dipnoi.html

Wirt Atmar
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