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

Re: BCF and BADD



> I don't have any problems with exaptation; I have problems with _fifty_ (or
> some other large number greater than three) exaptations all appearing
> together in one cursorial form.

     Could you clarify this?  I don't understand what you are trying to say.
 
> GUARANTEED many fewer generations than in the "ground up" scenario!

    It might make more certain that the mutations that appeared were 
selected for, but the mutations themselves appear when they are good and 
ready.  New genetic variety for natural selection to chose from appears 
no faster in a species in a life threatening situation than in a species 
that can afford to evolve at leisure.  An animals genes don't know what 
the species needs as far as mutations, the raw material for natural 
selection.   

> Not necessarily. Any measurable amount of fluff will help.

     True, but additional body feathers used for cushioning are not the 
same thing as big specialized flight feathers on the wings specially adapted 
for flight, gliding, or parachuting.  If this hypothetical animal started 
evolving cushioning feathers to break its fall, It still hasn't solved the 
problem of how to get its wing feathers big and developed enough to start 
parachuting or gliding.  Those are two totally different adaptations.      
     In fact, maybe developing this sort of padding would give the animal 
less reason to develop flight, as it would increase survival rates 
without wings.  

> Bigger feathers _would_ help, IF the animal were arboreal. There _would_ be a
> significant difference. But how could feathers help a cursorial form in any
> way? They would just get in the way--slow it down. If feathers and other
> long, hairy structures were so beneficial to cursorial forms, why don't we
> see more of them on ground-dwelling animals? Why do flightless running birds
> tend to _lose_ or _reduce_ their flight feathers? Why aren't big cats and
> dogs and hyaenas burdened with long hair?

     This is certainly a good point.  On possible exception to this rule 
might be the peacock, which has a huge, cumbersome tail whose only 
purpose is disply.  I'm not sure if peacocks can fly well or at all.  
If they can't, it would be a point in favor 
of bird ancestors being able to get by fine as crusorial forms with 
cumbersome display structures on thier arms.  However, an arboreal animal 
might indeed have more latitude for developing such elaborate structures 
since it would have less predator problems. 
 
> What other reason? Display? Insect catching? Why not look at it the _right_
> way, and understand that feathers evolved for trajectory control, and that
> _this_ was the preadaptation for display or insect-catching or whatever. Why
> not choose the likelier alternative first? I claim that the catch-all concept
> of "display" is a perfect example of the use of a structure that evolved for
> something else being suborned for sexual selection, species recognition,
> and/or rival intimidation. Thus, I would not expect feathers to have evolved
> _as_ display structures, but I would definitely expect feathers, _once they
> appeared_, to evolve into different shapes, sizes, and colors, reflecting
> (for want of a better term) various intraspecific preferences.

    But again, if feathers evolved originally for flight, we're back to 
the problem of intermediate forms.  Flight feathers may be the best 
and most logical  way to solve the problem, but getting them is the 
problem.  Those first feathers would not be big 
enough for any kind of trajectory control, or impact cushioning for that 
matter, and would need another reason to get expansive enough to be able 
to be used for these functions.  Again, an evolving animal isn't looking 
down the road towards the day that a trait it is deveIoping will be usefull. 
I still think the likeliest original function of feathers was insulation, 
later to be modified for display or something else that would cause those 
drastic enlargement and alterations of the wing feathers to be able to be 
used secondarily at first for parachuting (or flapping to get a little 
extra speed if the animal was crusorial), and then take off down the 
road for flight regardless of thier orignal function.
     However, the idea of feathers being developed first for insulation runs 
into basically the same problem of transitional forms as feathers originally 
being developed for flight.  A few little bristles on the offspring of 
those first naked archosaurs aren't going to do diddly for trapping 
heat.  Any suggestions out there for what those pathetic proto-feathrs 
might have been used for?      
  
> When you find something as compelling as solving the falling problem, or
> evading predation, which have obvious and immediate selective advantages,
> what reason would you want to look for something farther fetched? Becoming
> arboreal is an excellent way of solving the very immediate problem of evading
> a predator: just ask any squirrel that my dog has chased into a tree. Leaping
> from branch to branch in a tree or between trees likewise helps to solve the
> problem of what to do when the predator comes up into the tree after you.
> There is clear and obvious selection pressure to evolve better ways of doing
> these things.

     Those are good reasons for becoming ARBOREAL, but still don't answer
the transitional forms problem for trajectory control feathers, or impact 
padding feathers for that matter.  I'm not saying that dinosaurs and birds 
being descended from arboreal archosaurs is at all far fetched, or that these 
archosaurs didn't develop flight "from the trees down".  In fact, I think 
your arguments in favor of this are quite logical.  All I'm saying is 
that I find the idea of feathers in 
general and big, sophisticated arm feathers in particular being 
originally developed for flight highly unlikely due to the problems of getting
from here to there, and that preadaptation of some kind probably set the 
stage for later flight modifications. 

LN Jeff