[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Extinction of Dinosaurs

> This last sentence - I think inadvertently on your part - smacks of
> directional evolution, which I suspect most evolutionary biologists would
> regard as fallacious.  

      On the grand evolutionary scale I agree.  Reptile evolution was not 
directed twoard trying to produce mammals, mammal evolution was not aimed 
at providing humans, etc...  As I discussed in the posting, evolution 
is usually a strict matter of luck and contingency.  But if you look 
a smaller scale of evolution, and magnify on the physical adaptations 
that occur when contigency demands change,  I think "improvement" is a 
relevant concept.  
> Archaeopteryx  was not a "crappy flier" because it
> was on the way to becoming a better flier - there is no selective pressure I
> can imagine that would favour an adaptation because it might turn into
> something really nifty in a million years or so. Archaeopteryx flew the way
> it did (however that was) because doing so was adavantageous to it at the
> time (as you also say), and gave it, perhaps, an advantage over other even
> more inept fliers.  

     Hence the further improvements to the design.  No, a species does 
not "think ahead" when it is evolving, but if the system it has could be 
better, it will make modifications that are IMMEDIATE improvements to the 
     Its important to keep in mind that the features of Archaeopteryx that 
made it a relatively poor flier compared to modern birds were ALL PRIMITIVE.  
The lack of a big breastbone, pygostyle, triosseal [sic?] were ancestral 
theropod features, not features that might have been DERIVED to keep 
Archaeopteryx a relatively crappy flier because this was somehow more
advantageous to the lifestyle its ancestors began to adopt than being a 
better flier.      
     More glaring examples of improvment can be seen in atrophy.  As far 
as I know, Basilosaurus did not have those teeny tiny hind legs because 
they were great for scratching a teeny tiny area of its rear.  It was in 
the process of eliminating them.  An IMPROVEMENT on the aquatic design.  
If those little legs did continue to serve some function, it obviously 
wasn't enough to keep them from being eliminated.  Refining the body for 
an aquatic lifestyle took precedence over whatever use they may have 
     The improvement process is obviously going to be cancelled if an 
organism is pressured (or sees advantage) into taking a sharp left or right 
toward another life-style.  One example in the case of birds is the 
modifications of Hesperornis and penguins for an aquatic lifestyle.  In those 
cases, improvements stop being made in the flying design and start on 
making the wings or feet or whatever into better swimming organs.  
Improvement toward a design ends when selective pressures change.  The 
refinements I'm talking about may take place in short little jumps, but I 
think on that scale they can indeed be called refinements.  
LN Jeff
"I'm sure that the people of Elbonia are fully capable of governing themselves."
"Do you know what the national bird of Elbonia is?"