Re: Evolution: A few questions

From: bivalve <>
Date: Thu Jun 17 2004 - 17:17:23 EDT

>What happens during "however many generations" the organism exists with
> wings that were not yet functional? Wouldn't this be more
> detrimental thus causing the evolutionary process to drop the
> wings before they're useful?"
> A most reasonable question, we would all surely agree - and along the same
> lines as the assumed 'fish > amphibian' transition
> In my view, this hardly gets to the nub of things - indeed, it is as
> disappointing as the answer you gave me. Precisely how does an incipient
> wing confer selective advantage?

Glenn cited an article that showed that young ground-dwelling birds can get a boost when running uphill if they flap their wings, even though they cannot yet fly with them.

The "four-winged" dinosaur fossil from China, along with the numerous gliding animals and the probable arboreal (or other climbing) ancestry of bats and pterosaurs strongly suggests that vertebrate wings originated as parachutes or aids to gliding. Small, lightweight animals (which includes the vast majority of tree climbing species) already have a moderately high ratio of drag to mass. Even a rather rudimentary wing can be a big help in extending a glide or slowing a fall.

I'm not sure about the disappointment with regard to the fish-amphibian transition. The combination of good fossil transitional forms with living habits of modern lungfish and amphibians (as well as analogues like the mudskipper fish, which likes to crawl out of water onto the land) makes this transition very well-supported.

As I recall, the objection raised was that becoming an amphibian is a poor way to outswim carnivorous fish. However, being able to crawl into places where the carnivorous fish can't get at you is not a bad survival technique, either. Additionally, the early amphibians were relatively large, similar in size to the large fish in their habitat, so they did not need to worry much about predatory fish. Presumably their larvae were no worse at escaping predators than tadpoles are today.

The earliest fossil amphibians, like many modern ones, were apparently still aquatic. The first fossils probably used both lungs and gills to breathe, just as lungfish do. All amphibians can breathe through their skin and mouth lining; some have neither lungs nor gills and rely entirely on this. Thus, transitioning from gills to lungs is not a big deal.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL 35487-0345 USA

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa
Received on Thu Jun 17 17:40:47 2004

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