[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Lemurs and Feathers



> I don't think we have anywhere near exhausted the scenarios for the
> development/evolution of wings >directly< for flying, by incremental
> improvements in a feathered forelimb.

Surely possible... such as? :-)

> Yet we have scenarios of wings
> developing for brooding and wings

no, flapping

> developing for underwater locomotion before
> being exapted for flight. I think people have become too enamored of the
> exaptation concept and are throwing it at avian flight with altogether too
> much abandon, without looking at the common sense of the situation.

The exaptation concept makes a lot of sense in other cases, such as the
origin of tetrapods respectively land-living. E. g. *Ichthyostega* had no
(internal at least) gills not because it lived on land (which it didn't),
but because it lived on the oxygen-poor bottoms of bodies of water and had
_therefore_ to rely on its lungs for breathing. Ref: Carl Zimmer: At the
Water's Edge. Macroevolution and the transformation of Life; full citation
tomorrow, if someone wishes

> Does it
> make sense for an animal to evolve wings for brooding, only to have them
> happen to be perfect for flight? Does it make sense for an animal to
evolve
> wings for swimming underwater, only to have them happen to be perfect for
> flight?

IMHO these are examples of wrong questions (rather than wrong answers). It
is of zero interest or importance to an animal that evolves wings for
brooding what its descendants will or won't do with them millions of years
later. Same for swimming. Or for lungs -- the _placoderm_ *Bothriolepis* had
lungs and surely never came out of water.

> This reeks of miracle.

No, of macroevolution :-) :->

> Why not simply have the animal evolve a
> rudimentary wing from a feathered forelimb that helps it to negotiate in
an
> arboreal lifestyle,

How exactly? All scenarios that I know so far -- I probably can't claim even
representative knowledge of the literature -- reek of miracle or at least
severe improbability to me.

> and then have these selfsame wings gradually improve,
> until they're capable of sustained flight?

Oh, that's an exaptation likewise.
BTW, there are good arguments that manoeuvering and landing skills must
develop before the capability of takeoff (in Pat Shipman's Taking Wing).
Underwater flight provides a scenario in which the flapping movement (and
the aero-/hydrodynamic wing shape etc.) can be perfected without having to
be perfect from the beginning, and without constant danger of extinction due
to failure, but with steady selectionary pressures to perfection. (Partly
hypothetical example -- underwater flight should be possible with
symmetrical and asymmetrical wing feathers, but better with the latter [and
both are suitable for brooding]; flight in air is apparently next to
impossible with symmetrical and asymmetrical wing feathers. So, if we assume
symmetry to be plesiomorphic [no direct evidence here], then asymmetrical
flight feathers can have developed underwater, but no flight feathers at all
can have developed in air, without an exaptational scenario that I'd like to
read.)

> These wings could easily be
> exapted for brooding, underwater swimming, whatever you like, at any stage
of
> the scenario, as many times as you like.

Sure.