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Re: flights of fancy (or "I'm brave, but I'm chicken****")



In a message dated 95-12-01 19:08:39 EST, rowe@lepomis.psych.upenn.edu
(Mickey Rowe) writes:

>There are really times when I wish I had more free time...

I don't have much myself, so when I get a humongous meaty response like the
following, I cringe at the work involved in properly replying.

>A lot has been said about the origin of flight and what modern animals
>and fossils can tell us about it.  I've been wanting to jump in for a
>while, but only now find some time to actually do so.  I'll try to be
>brief, but I fear there's a lot I want to comment on...

"Brief"?

>First for an overall perspective: It seems to me that what we *don't*
>know about how flight evolved in various animal groups *vastly*
>outweighs what we do, and the certainty with which various statements
>have been made on this list really bothers me.  I'm glad Ronald jumped
>on George for that, but I don't think George is the only guilty party.
>In any event, on to specifics...

Certainty is a relative thing. I'm _almost completely_ certain that theropods
in particular and dinosaurs in general originated as side branches off a
lineage of arboreal archosaurs. Other people probably require more convincing
about this than I do.

>LN Jeff stated the opinion that protofeathers wouldn't help much in
>protecting an animal from a fall, and George replied:
>
>> Not necessarily. Any measurable amount of fluff will help.
>
>I don't think this is a worthwhile assessment of the situation.

Given one sentence and half a minute to compose a reply in, sure it is. I'm
not going to write a treatise on the merits of fluff as an airfoil and then
send it out on e-mail.

>While
>it's probably true that any elastic and durable (or better yet
>regeneratable) coating should help an animal survive impact, it's not
>kosher to look at the feature's advantage(s) in isolation from its
>disadvantages.  "Any measurable amount of fluff" will also tend to get
>tangled in branches leading to all sorts of problems if it is not also
>controlled (e.g. with piloerector muscles) by its arboreal bearers.
>Nevertheless, if George's idea were correct, one would expect that the
>animals most likely to be involved in potentially injurious falls
>would be those most likely to have protective coverings.

Fluff isn't just a protective coating. It also has the advantage of
increasing air resistance and thereby cushioning/slowing a fall.

>Has anybody
>ever considered testing such an idea by doing a comparative survey of
>the density and mechanical properties of hair and feathers across a
>large number of cursorial vs. arboreal animals?  George, wouldn't you
>think that sort of science is better than the "Just So story" you're
>pushing with the above statement?  Barring such an analysis, I fear
>that George's statement is just so much fluff (God, the puns are
>flying thick around here!)

Sure--give me a plush grant and five years, and I'll be happy (well, not very
happy, but at least it would pay) to survey the mechanical properties of hair
and feathers. You're talking _real work_ here, something to which the e-mail
medium is not terribly adaptable. Plus, after five years and the grant, I
would still have only a Just So Story--though perhaps a more detailed one.

>George continues:
>
>> 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.
>
>This is a rather traditional assessment of the situation which Ronald
>has also stated with an IMHO undue amount of certainty.  Personally, I
>think LN Jeff is on to something with his question about chickens.
>I'm glad that Glen Kuban took him seriously, and I hope others will as
>well.  Like Betty, I grew up with chickens in my back yard (though I
>never really thought of any of them as "pets").  I didn't torture them
>like Jim Farlow did his emus ;-), but I certainly chased them
>occasionally (even though this was before "Rocky II" was released ;-).
>Based on what I've seen, I'd say that chickens use their wings in two
>different ways when evading a "predator".  Regardless of whether or
>not they're "trying to fly", they do generate thrust with their wings.
>It is thus NOT necessarily true that the presence of feathers will
>slow down a running animal.  If the feathers are tucked in while the
>forelimbs are moved forward during the recovery phase and spread out
>during the backwards directed power stroke, the animal can conceivably
>propel itself with it's proto-wings even if it's not capable of
>generating enough lift to overcome its weight.  As for the statement
>that this sort of behavior would tend to pull the feet off the ground,
>I disagree.  Before the behavior is well developed, there's no reason
>to suppose that the animals would "try to fly" just because their
>descendents eventually could.  Keep in mind that spoilers on cars are
>designed to keep them on the ground, so wings don't always make an
>object go up.

In this scenario, I would say the chickens are trying to overcome the
disadvantage of being stuck with wings that don't help them run very well.
The idea of cutting back the wings to see whether the chickens could run
faster is an interesting one, but somehow I (at least) wouldn't have the
heart to perform the experiment. (Are any of those Nazi scientists still
around?)

The question is whether feathered wings would evolve as an aid to running--as
something whose existence confers an advantage on a bipedal cursorial
animal--and I just can't see that happening. If this were true, why do
sprinters and marathoners wear so little clothing when they run? Why wouldn't
they, instead, don fake feathers on their arms to help themselves run faster?
Well--they're not six inches tall and lightweight. But I think the principle
is the same.

>The other behavior that chickens use their wings for is the rapid
>change in direction.  Roadrunners do this too.  By throwing their
>wings around and/or generating asymmetrical power strokes, these birds
>can cut back better than any football player.  It's those sort of
>maneuvers that make roadrunners hard to catch (I've chased them too)
>rather than their cartoon-fabled speed.
>
>My point is that proto-feathers are not necessarily the hindrance that
>they are normally purported to be for cursorial forms.  I think the
>"energy budget" argument that Ronald and George are pushing is
>overblown.  I think we know so little about how flight developed that
>we can't exclude any particular avenue at this point.

Again, I think this is an example of a case of the animal trying to make
lemonade out of a lemon. Do you really imagine that feathered wings evolved
to make a small, cursorial animal more maneuverable on the ground? Or is it
more likely that, having been handed feathered wings as part of its heritage,
the bird uses them the best way that it can?

>And on the topic of assumptions, LN Jeff stated:
>
>] 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.
>
>As Nick pointed out, we now have pretty clear evidence that the above
>is false with respect to at least some forms of bacteria (yeast, too,
>I think).  While the specific mechanisms used by these organisms can't
>be used in the same way by multicellular animals, it at least woke
>people up to the idea that mutations may not be perfectly random in
>their time of appearance.  Our cells use various enzymes for error
>correction in the copying of DNA strands -- there's no _a priori_
>reason to believe that organisms can't control the functioning of
>those enzymes (and/or the proteins involved in controlling
>recombination events) with respect to environmental pressures.  That
>is to say, it could well be advantageous to up your mutation rate
>during hard times.  Granted this doesn't mean that organisms can
>lengthen their descendents' necks by reaching for leaves in tall
>trees, but it does mean you might be more likely to leave relatively
>long-necked descendents when there are fewer leaves available to you.
>I'm not saying this does happen, but only that you've got to keep an
>open mind.

Lamarckism in macro-organisms seems extremely unlikely to me.

>In response to Ronald's claim that flight might have evolved for niche
>expansion rather than predator avoidance, George claims:
>
>> [reaching new sources of food was] Not as important as escaping
>> predators, because the animals cannot know in advance that food will
>> be found in new regimes.
>
>To me this sounds like pure and simple arm waving.

You mean, wing flapping.

>Animals also
>cannot know in advance that feathers will help them fly away from
>predators.  Or put the other way, the mechanisms that result in
>genetic variance didn't know that giraffes could reach more food if
>they had longer necks than their ancestors did.  That "argument" seems
>like a non-starter to me -- one made more because George already
>believes the conclusion than because it makes any real sense.

But I never _said_ that feathers will help protobirds escape predators. It is
_climbing into trees_ that does this. The feathers help to solve the falling
problem once they're _in_ the trees, not the escaping problem. Feathers or
pre-feathers have nothing to do with escape from predators (in the beginning,
at any rate).

>George seems to have understood the principles better when he wrote:
>
>> Chickens have wings, albeit not particularly flightworthy ones, and
>> they'll use them however they can.
>
>As would their pre-flight-capable ancestors.

Yes, indeed! They would use them for (among other things, such as display)
controlling their trajectories and parachuting as they leap/fall from
branches/fronds. Here's another heartless chicken experiment: Climb up into a
tree with a bunch of chickens. Leave some with their wings free, others with
their wings bound to their bodies so they can't fly and the wings can't break
their fall. Drop the chickens out of the tree, then see which ones accumulate
the most injuries from the fall. I bet I know which ones they'll be.

>Also in response to LN Jeff, Kata McCarville suggests:
>
>} In the case of a fleeing chicken, since chickens have a fairly high
>} birth rate, maybe the intent is to draw the predator away from the
>} flock, even at the cost of the individual's life.
>
>I try to be open minded, but the above is an argument based upon group
>selection, and evolution doesn't seem to work that way.  Individuals
>don't develop characters because they are good for the species as a
>whole; they develop characters that are good for their descendents in
>particular.  You can see the distinction in the scenario reported
>above: the animal with the trait in question is having its life cut
>short, thereby making it less likely to leave descendents than its
>conspecifics that don't have the trait...
>
>On another subject, George claims:
>
>> The problem is not with the evolution of flight, it is with our
>> present inability to imagine the stages in which this evolution took
>> place.
>
>It seems to me that the problem isn't our inability to imagine, but
>rather our inability to find enough evidence to support any one of the
>pathways we have imagined to the exclusion of other possible paths.

That would be another--better--way of putting it.

>Back to George:
>
>> _Archaeopteryx_ undoubtedly had several (probably tens of) megayears
>> of flight evolution in its ancestry in order to have evolved the
>> flight feathers and other adaptations for flight observed in the
>> specimens.
>
>I'd lose the "undoubtedly" if I were George.  While George's stance
>does seem plausible, the pace of evolution is a neat area of current
>research (I'll refer people again to Jonathan Wiener's _The Beak of
>the Finch_), and it seems extremely premature to argue about the
>strength of the pressures selecting for flight in birds when we can't
>even comfortably conclude what the pressures were.

I felt my choices were between "several" and "as much as a hundred." It's not
the pressures, it's the quite considerable amount of very specific anatomical
change that _Archaeopteryx_ must have undergone. I can't imagine that
happening overnight. If BCF is correct (and of course, I think it
substantially is), then there would be substantially fewer kinds of theropods
in the Jurassic fossil record if the evolution of flight feathers and other
flight adaptations in _Archaeopteryx_ occurred swiftly.

>As for Glen's recommended experiments...  I don't think you need to
>pluck chickens to learn what you want to learn.  All you need to do is
>film them with a high speed camera and analyze their motion from frame
>to frame.  That is, you can plot their speed as a function of what
>their wings are doing and verify my qualitative observations reported
>above.  That way all you need to do is chase them and film them.
>Sounds like a perfect job for Jim ;-) (though he'd probably want to
>get them to run across sand or a force plate and look to see if Ron is
>right about them leaving the ground when they flap ;-)

Hey, we're talking serious grant money here again.