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[longrich@phoenix.Princeton.EDU: Re: Feathers vs other insulators]



Sender: Nick Longrich <longrich@phoenix.Princeton.EDU>
Subject: Re: Feathers vs other insulators

On Tue, 8 Oct 1996 martin@hpentccl.grenoble.hp.com wrote:

> If this were so, I would have expected animals living in cold
> conditions to have evolved hairs mimicking feather structure. But as
> far as I know (and I'll probably be told otherwise!) they don't; what
> they do evolve is different hairs in different densities. Feathers are
> good insulators, sure, but I don't see how they can be "better".

        Some people say that feathers evolved for flight, but if this were
so, I would have expected animals that evolved for flying and gliding to
have evolved aerofoils mimicking feather structure. But as far as I know,
they don't; what they do evolve is different sizes and shapes of skin
wings supported by different structures (ribs, varying numbers of fingers,
toes, arms, legs, fins, tails). Feathers are good aerofoils, sure, but if
they never evolved in any other animals for this purpose, why should we
expect them to have evolved for flight?

        No sarcasm is intended, I'm just showing how we can develop an
argument using similar structure on exactly the same evidence. We just
CANT USE the uniqueness of feathers to argue one way or another. "well, if
they're such darned good insulators, how come polar bears don't have
them?" is easily met with "well, if they're such darn good aerofoils, why
don't bats and flying fish have them?" They have their disadvantages, but
they are arguably the best aerofoil design there is (replacable, less
easily damaged, capable of some mean variable geometry, able to be evolved
into a wide range of wing shapes, don't demand a leg attachment) and they
are to the best of my knowledge, the best insulators found among animals,
period(their structure helps trap air more effectively, I assume, than
the simple straight fibers of mammalian hair. An interesting notion-
both of these functions have to do with controlling the flow of air-
so they're not so different as we think?). Feathers serve two purposes
very superbly and nothing nowhere ever evolved anything else like them for
either purpose.*

        *okay, so there is thistle-down, which resembles ratite plumage,
and there's probably others. Ah, yes, the hind feet of diving beetles
(dytiscids) in the adults, and all the feet in the young, are lined with
hairs that catch the water, making them into vaguely feather-like oars. So
there are those, too. 

        Nick L.