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Re: Feathers [was: Re: Q's arising from Archaeopteryx feathers]
In a message dated 96-10-01 21:02:11 EDT, firstname.lastname@example.org (Jonathan R.
> I do not agree. There is a significant body of scholarly work
> devoted to the endothermic dinosaur theory. Along with it have come
> comments about the evolution of feathers. I have yet to see major scholarly
> work onthe subject, but considering that nearly every biology textbook has
> the "scales-to-feathers" diagram, I assume that the homology is well
> established (PG, feel free...).
The scales-to-feathers scenario is being eroded by equally scholarly work
(see prior postings by Alan Brush, e.g.) that suggests feathers are a
neomorph that appeared independently of scales. Different structures for the
keratins of feathers and scales, that sort of thing. So the homology is >not<
well established, and if it happened to be so in the past, that was a kind of
fool's paradise: "scholars" pulling the plumage over everyone's eyes.
> I have not heard of a hypothesis which says [feathers] evolved
> specifically *for* flight...
Well, keep reading Feduccia's new book.
> "Just So" stories tend to be a phenomenon associated with poor
> theoretical knowledge, and/or incomplete or simplisitic thought. They
> almost always involve a simplification of a process...
Just So Stories provide a framework for research, and thus constitute the
first stage of thought in the assembly of a theory. In formulating such
scenarios, details are omitted in order to perceive the Big Picture. In
principle, Just So Stories have nothing to do with poor theoretical knowledge
or simplistic thought.
> 1) All of the full-body "hairlike" integument that exists is used as
> insulation (although it does have other uses...).
This use can always be explained as an >exaptation< of feathers from an
original purpose for parachuting/gliding/flying.
> 2) There are many arboreal animals which have not developed feathers
> or other integument to soften their falls...
They had helpful mutations other than feathers. The >appearance< of feathers
or any other feature is not compelled in any lineage for any reason;
otherwise all living organisms would look alike. But once "pre-feathers"
appeared (for we all agree that feathers are too complex to have evolved all
at once, "overnight"), whatever advantage they conferred allowed them to
evolve into true feathers. This advantage, whatever it was, is considered the
"reason" that feathers "evolved." Maybe it was for insulation, but this has
>not< been definitely established (see Feduccia's new book, for example, for
some good arguments against the feathers-originated-as-insulation
hypothesis). I think it's likelier that they initially helped to solve the
Falling Problem (which we >know< exists for arboreal animals, at any rate) in
dino-birds, particularly since it seems that dino-birds may not have been the
fully endothermic vertebrates we all thought they must have been.
> 3) Birds are warm blooded...
As I said, feathers could easily have been exapted to serve as insulation,
once birds became endothermic.
> All of these things make the conclusion that feathers were
> origionally developed for a purpose other than flight (or falling out of
> trees) the more parsimonious theory. Display is certainly possible, and so
> is insulation.
In the end, we must ask why, given their obvious utility in flight, should we
consider it unlikely (or "less parsimonious," as cladists would put it) that
feathers >actually evolved for that purpose<? BADD paleontology is full of
scenarios in which one theropod feature after another evolves for some reason
>other than< flight, only later to be found marvelously exaptable for
flying(!). Why not, at least as a working hypothesis, instead assume that
these features actually evolved as incremental improvements in the evolution
of flight? That, in a nutshell, is where BCF comes from.