Evolution is not progress?

Gene Spears spears at bobcat.lmc.edu
Fri Jun 26 09:48:16 EST 1992


In article <1992Jun25.041642.24544 at news2.cis.umn.edu> thomasc at lobachevskii.geom.umn.edu (Thomas Colthurst) writes:


>Occupation of a "larger" enviornmental niche could be considered one
>_aspect_ of progress, but even this criteria is very problematic.  For
>one thing, I believe that studies of # of enviornmental niches occupied
>versus time show that this index actually decreases rather dramatically.
>There is a general pattern of life form diversification followed by
>extinction of most of the branches.
>  

	Although this is a little off the track of bionet. *molbio*. 
evolution, an excellent example of this can be found in the class Reptilia.  
Numerous groups of reptiles have undergone explosive radiations, moving into 
marine, fossorial, and arboreal enviornments, only to go extinct and be 
replaced by another, unrelated group that undergoes a similar adaptive 
radiation.  Before our diverse assemblage of modern lizards evolved, their 
ecological niches were filled by an extinct group, the eolacertilians.  
There were eolacertilian analogs of modern-day skinks (burrowing lizards), 
_Basiliscus_ (a bipedal lizard, sometimes called the Jesus lizard cause it 
can run across the surface of the water), and _Draco_ (a gliding lizard).

To the larger question of whether evolution ----> progress, the term 
progress is so ambiguous that I suspect the answer will depend on how you 
define the term.  Over a large time scale, evolution has led to increased 
species diversity, and, in a sort of positive feedback cycle, increasing 
diversity increases the number of ecological niches available, thereby 
leading to more diversity.  Ex: When large, rapidly-swimming fishes evolved, 
a new niche opened up for fast, agile predators.  Ichthyosaurs filled that 
niche during the Jurrasic; dolphins fill it now.  Did Ichthyosaurs 
represent "progress" in the Jurrasic?  Do dolphins represent "progress" over 
the ichthyosaurs?

G. Spears
spears at andy.lmc.edu



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