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Re: book reviews, parsimony and some loose ends



In a message dated 96-10-25 17:10:45 EDT, martz@holly.ColoState.EDU (Jeffrey
Martz) writes:

> BCF proposes exaptation as well, whether you realize it or not.

Of course it does. BCF exaptations, however, are not nearly as >wild< as
those proposed by BADD. Forearm feathers as insect traps (ever try to trap a
fly with a feather duster?) that later become wings! (I must admit, however,
that this one is getting too far-fetched even for BADD paleontologists.)

> You have feathers originally evolving as padding for dino-birds
> falling out of trees.  This is not flight.  Neither is using long
> grasping fingers and claws as climbing tools.  Later using these
> long CLIMBING fingers to control feathers in FLIGHT would however be
> a primo example of exaptation.  Saying that that falling (not
> parachuting or gliding) and climbing abound in trees are early
> stages of flight just because the animal's feet aren't touching the
> ground is bogus.

"Bogus?" Saying that RUNNING and JUMPING (off CLIFFS, in one paper I read!)
are early stages of flight, a la BADD, now, that's BOGUS. Powered flight is
too complicated an activity to have evolved overnight, without a significant
stretch of evolutionary history in a flight-friendly environment (such as
trees). To this extent, yes, climbing and leaping around in and falling out
of trees are >indeed< "early stages of flight." You bet they are.

At any stage in the evolution of flight, some (most?) lineages simply become
extinct, some lineages do not evolve the necessary improvements to pass on to
the next stage and remain stuck as arboreal climbers, gliders, and so forth,
and some lineages return to a cursorial lifestyle and continue to evolve and
diversify into terrestrial forms (such as dinosaurs from dino-birds), losing
their less useful arboreal features. But we >know< that at least one lineage
at each stage did evolve the adaptation(s) necessary to reach the next stage,
because we have fully volant birds today.

So, in the final analysis, who's to say what's a "stage in the evolution of
flight"? In some lineages, for example, the stages in the evolution of flight
are merely stages in the evolution of bipedality.

>  Arboreal animals like monkeys are squirrels are NOT in the early
> stages of flight. However, if they chose to modify characteristics
> used for an arboreal lifestyle for flight later on, this would then
> be exaptation.  BCF and BADD both have the same problem: taking a
> GRAVITY BOUND creature and getting it airbourne, and both probably
> aren't going to find a solution without exaptation.

I don't recall ever saying that BCF provides an exaptation-free explanation
of the origin of avian flight. What BCF provides is an environment (arboreal)
in which flight-friendly evolutionary features can already be useful at their
initial appearance, ripe for exaptation into an ever-more-volant lifestyle.

Feathers or pre-feathers on a strictly ground-dwelling animal may or may not
have had their uses, but on an arboreal animal they provide several clear and
positive advantages, such as the ability to ease a fall and to provide some
measure of directional control during leaps between branches. It is perfectly
natural that organs abetting such functions would be selected for, and
perfectly natural that, given the appearance of feathers in an arboreal
animal, feathers would in descendant lineages become modified to serve as
organs of flight.

I submit that wing feathers and wings on ground-dwelling animals are a
>liability<, based on the large number of known, extant ground-dwelling birds
in which the flight feathers are modified into hairlike vestiges and the
wings are strongly reduced. To me, this says that feathers >won't< become
flight feathers and wings >won't< evolve at all in ground-dwelling, cursorial
forms. An arboreal environment and lifestyle are >required< for the evolution
of powered flight. If the evolution of flight can happen from the ground up,
why is there not a single known instance in which flight has re-evolved in a
lineage of cursorial, terrestrial birds descended from flying ancestors? One
would think that, with so much of the equipment for powered flight already
present in such cursorial avian lineages, re-evolution of flight would be a
simple matter.

>      There is nothing particularly "miraculous" about exaptation.
> It is a logical way of getting from A to C.  Just about any trait
> used by a living organism for more than one purpose is a potential
> source of exaptation.

You think I don't understand this?

The miracle to which I refer in the BADD hypothesis is the appearance of so
many of just the right kinds of exaptations, all in a single lineage of
cursorial dinosaurs, that powered flight just >happens<, so that cursorial
dinosaurs can just take off from the ground by running and flapping their
well-feathered arms. This, I submit, is utter nonsense.