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
