RE: Evolution: A few questions

From: bivalve <>
Date: Mon Jun 21 2004 - 20:24:15 EDT

> What concerns me - and, I believe,
> > Jason also - are the earliest stages of this alleged process,
> > when the normal functions of the creature concerned must be
> > impeded (and thereby diminished) by changes which, though
> > possibly producing a selective advantage in the long run,
> > render it particularly vulnerable to extinction at the time
> > (and continuing).

The normal functions of the creature need not be impeded; this will depend on the particular innovation. The novel features that generally get the most attention (e.g., amphibian feet) tend to provide critical ability to take up new habits. As such, they generally provide an entry into a relatively vacant niche. Competition is low, and the chances of survival are enhanced.

For example, the transition from gill-breathing to lung-breathing involved fish and amphibians that used both. This allows breathing underwater to be supplemented by the abundant oxygen in the air. Many kinds of fish today have some way to breathe air, especially those that live in stagnant water or that come out of water. Thus, the innovation did not impede the normal function; rather, it enhanced it by providing a better oxygen source.

The sarcopterygian (lobe-fin) fish thought to be most closely related to amphibians have well-developed leg/arm bones. One specimen from Pennsylvania of a fish limb even has the foot bones, as well as the fin rays. Modern aquatic tetrapods often have webbed feet, providing as good paddles as the lobe-fin fish had; however, for fast swimming, limbs are generally held close to the body and undulation of the body or movement of the tail is used for propulsion. Either way, feet aren't a big change nor a big hindrance.

The success of a new feature leads to increasing pressure to improve it (or more accurately, selective pressure favoring any improvements that may appear) due to increasing competition among those with the new feature.

Also, the novel features that get a lot of attention are the successful ones. Probably quite a few potential early stages did go extinct.

    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 Mon Jun 21 20:57:09 2004

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