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Re: Arms into wings



In a message dated 3/3/99 10:16:51 PM EST, TomHopp@AOL.COM writes:

<< The roadrunner stays landborne until it's sparring with prey causes it to
leap
 into the air. Then it flaps to stay aloft. It would be easy for a brooding
 biped to utilize its feathers for this, because the feathers must already
have
 evolved a streamlined, rigid form just to perform their brooding function and
 keep tucked out of the wind when not needed.>>

Roadrunners are already quite capable fliers, so the point is moot: In this
instance, flight did indeed come first. What you want is a bird that exhibits
this kind of behavior but whose lineage is entirely flightless (not just
secondarily flightless)--and there is no such bird extant.

<<It's just as arbitrary to insist that flight came first as it is to suggest
brooding first.>>

No, because extant birds use flight feathers (as defined by their aerodynamic
properties) for brooding, not brooding feathers for flight. I'm quite sure
that many, many more birds use their wings for flying than for brooding. So it
is much more straightforward to regard brooding as a flight exaptation rather
than flight as a brooding exaptation.

<< Flight adaptation does not automatically provide a brooding-capable wing,
so George's argument is relying on some self-satisfying requirements (that a
flight wing is "just right" for exaptation to brooding).>>

Nobody knows what the "perfect" or "just right" brooding wing might be,
because wings are generally also used for flying. Can you exhibit a bird that
uses its wings for brooding but not for flying? Can you list the
characteristics or features of a wing that you would consider to be obligatory
for a brooding capability? In other words, what features of a wing are present
solely because the wing is used as a brooding organ, that presumably arose
first, before the wing became a flight organ?

<<     I am willing to meet half way. Maybe brooding and flight co-evolved at
 precisely the same rate, given that they are both critical survival issues
for
 birds. >>

There is little doubt--it is, indeed, quite certain--that bird wings acquired
many different uses besides flight during the course of avian evolution. They
are presently used for display, for brooding, for defense, for shade, for
intraspecific combat, and for swimming, in addition to flight. But their
predominant use--the thing they are most suitable for, and the thing that no
other part of the bird's anatomy could substitute for--is flight. If you wish
to argue that wings evolved for some other purpose and later became exapted
for flight, then the burden must be on you to present a compelling argument
why this counterintuitive scenario occurred. So far, I haven't seen it.