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BCF etc



 --Ronald I. Orenstein recently wrote:

< The only real "proof" that an animal is secondarily flightless, or has secondarily lost exaptations for flight, is a phylogenetic analysis showingthat it is derived from an animal that flew or possessed the structures inquestion. So proving or disproving BCF comes down, in the end, to establishing phylogeny - anything else is speculation >

I don’t know where you get the idea that phylogenetic analysis *proves* anything Ron – it’s weak link is using the principle of parsimony. It’s ok to use Occam’s razor, but as a guide – I hardly need list examples of where it is violated. Each one of these *proves* that its use as a hard and fast rule (especially as a proof) is inapplicable.  And there's nothing wrong with speculation - a very high percentage of what appears on the list is speculation - including all the cladistic inferences.

<Surely this depends on what model of ground-up you are talking about. The "running-along-flapping" model, perhaps; but fluttering (as I have suggested,though I wouldn't go so far as to call it a hypothesis), leaping from rock torock, etc., perhaps not. >

What kind of argument is this? Why is fluttering acceptable but running along flapping isn’t? (I would say neither is.)

< I would say that any climber that must hold its body away from the trunk of a tree needs an attachment point above and below the centre of gravity to do so - that is, an upper suspensor and a lower brace. >

Consider a wall at the y axis (x=0), and a body with a centre of gravity at (x=1, y=2),  and a strut from this point to the wall at (x=0, y=1), and another below it to the wall at (x=0, y=0). 

< However, it is now believed that tetrapod limbs evolved before tetrapods crawled out onto the land; the question is whether the structure concerned is advantageous to the animal where it is, not its degree of complexity. >

All freshwater species experience some evolutionary pressure from repeated experiences of being stranded or nearly stranded in drying water. This may be small, but just think of all the fish-type species with pectoral and anal fins in pairs under the body and a single dorsal fin on top. Common ancestry of course, but surprisingly little divergence.  Maybe stability while temporarilly stranded out of water has something to do with it, even if not every fish can ‘perch’ upright on its fins.  The point is that there was no "*point as such* at which (anything) crawled out on land",

< Storrs Olson argues that in many ways the flightless ratites DO resemble large chicks, in feather structure, limb proportions etc. Alan Feduccia, in his article on flightlessness in "A Dictionary of Birds" (Poyser 1985), states that "Whatever the relationships of the various ratite groups.. they show similar neotenic features to those found in other flightless birds." >

The paedomorphosis argument has been refuted.

(. . . both by the argument on general principles by myself and George (in his case, many, many times) and again by Darren's very detailed approach.  We have to rely on people being reasonable and accepting when an issue has been settled.  It's not really possible to prove anything in this subject but without some willingness to accept when something that is as dead as the P thing is, there's no point saying anything at all.)

With regard to the discussion on asymmetric aerofoils, the asymmetry of feathers has a slightly different significance. The wing didn’t need to be a nice aerofoil to give some kind of aerial benefit, though it would have rapidly evolved towards one; and it didn’t even need its feathers to be asymmetrical to have an asymmetrical wing. It is generally agreed that the asymmetry of feathers is exploited mainly in their use as forward thrust providers in the downstroke: the longer trailing edge behind the feather vane or whatever its called tending to rotate the feather into an angle which provides thrust (incidentally a faster downstroke automatically and luckilly tending to produce a shallower angle of attack, better for faster air speeds). Elementary I know, and in fact I’m sure I’ve seen this agreed on the list some time ago. But the point is Archaeopteryx’s feathers were asymmetric because it pushed itself through the air. They prove it was more than a glider.

(BTW, one of the earliest uses of genetic algorithms in engineering was to find the optimum shape (in some sense of other, but involving minimum eddyfication I think) of a deflector plate for use in a wind tunnel.  It turned out to be a flat plane (which they knew already).)

On a related theme, I invite you to imagine how useful it would be to an animal that could provide some forward thrust, to be able to take off from the ground. Personally, I think no species with some thrust ability, could go more than, say, one hundred generations, without the ability to take off from the ground becoming common throughout the gene pool, unless there were very unusual circumstances applying. (In the case of swifts, the incentive to re-evolve take-off power is low since they never land on the ground.)

-- Ralph Miller III recently wrote:

< What evidence would it take to establish that BCF (George Olshevsky's BirdsCame First scenario) was supported by a preponderance of evidence over BAMM (Birds are Modified Maniraptorans)? >

"We need a sequence of forms each so similar to the next that half the experts say they are the same species, between a flying form and the flightless descendant. Only then will the necessary methodological changes be made – but such a sequence of dinos will never be found."  As true now as when I sent it to the list three weeks ago.  In fact, evidence is in the eye of the beholder. The meaning of what is in front of your eyes depends very strongly on the beliefs inside your head.

On the subject of birdoids such as Steamer Ducks using their wings as clubs, how many of them have claws, and what shape are they?  I claim that claws do not make good high-impact-delivery systems, particularly dromeosar claws.

 

John V Jackson    jjackson@interalpha.co.uk

"We are not a team."