RE: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

[Tim Williams <twilliams_alpha@hotmail.com>]

Don Ohmes wrote:


> Sure. And/or accidental collisions while gliding from tree-to-tree, leading 
> to hawking and echo-location.> The space between the trees was presumably 
> under-exploited by insectivorous birds at night. Hence 
> the success of the bats at moving in.


As David M. said, _Onychonycteris_ supports the hypothesis that flight preceded 
echolocation in chiropteran evolution.  Flight first, echolocation later.


BTW, the origin of bat flight might have been helped along by saltatory 
morphological change - in this case, elongation of the wing digits (Sears et 
al., 2006; PNAS 103: 6581-6586).  This might have been the catalyst that 
promoted powered flight in bats, rather than just an ecological opening that 
was available for exploitation.


> Exactly! On the gravity-driven side, you have every animal that can or will 
> leap, fall, or pounce from a 
> high place for natural selection to act upon. 


Such a statement is only relevant to the origin of bird flight if (and *only* 
if) the ancestors in question did indeed leap, fall, or pounce from high 
places.  Because bird flight only evolved once, we have a sample of only one 
(n=1).  So discussions about which process is "most likely" to occur are 
entirely beside the point.  


Natural selection is worse than short-sighted: it's totally blind.  If a small 
proto-bird is leaping from the ground against flying insects, and such a 
behavior is beneficial, then there's no reason why natural selection would not 
act to improve this behavior - despite the cost (more energy required to fight 
against gravity).  It's not as though natural selection is going to say to the 
proto-bird: "Hang on - this would be so much easier if you learnt to climb 
trees, and let gravity help you.  I'm pulling the plug on this experiment.  Get 
yourself up a tree, and then we'll talk!"  


Not that I'm actually advocating this Ostrom-esque "ground-up" insect-catching 
scenario.  All I'm saying is that your perception that it's more energetically 
challenging than a gravity-driven scenario cannot be used to refute "ground-up".


> On the muscle-driven side, ya got nothing but your 
> imagination and a long list of "ancestral constraints". As any manufacturer 
> can tell you, the availability 
> of feedstock and ease of manufacture all count when assessing the likelihood 
> of success.


This (dare I say) is teleological thinking.  Evolution does not have foresight, 
so it cannot make judgements about which pathway is more likely to lead to 
success. 


To use an example in the reverse direction (loss of flight, rather than 
gain)... If a manufacturer were designing a dodo, they would probably let it 
keep its flight ability, in case a new predator arrives on its island habitat.  
But natural selection doesn't employ forward thinking, and only acts to select 
for what's beneficial in the immediate term, regardless of the long-term 
consequences.   (Now if only I could think of an analogy for this in the 
business world... Hmmm...)


> Exactly! This is why the "climber-friendly" nature of cycads is important. 
> Cycads can be utilized by 
> animals that are optimized for non-arboreal forms of locomotion. Roosting, 
> perch-hunting, gleaning,
>  even nesting are physically possible, and arguably advantageous...


I don't disagree.  What I don't understand is why this scenario cannot be 
combined with terrestrial behaviors, especially those that involve leaping. 


> I did not realize the the non-existence of gliding behavior in proto-birds 
> had been proven...


It hasn't.  But gliding behavior in proto-birds cannot be *assumed* simply 
because it offers an "easier" (in your assessment) route to powered flight.



Cheers

Tim
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