Re: [asa] Punk EEK: was Arrogance ....

From: David Campbell <pleuronaia@gmail.com>
Date: Fri Aug 24 2007 - 12:18:28 EDT

> > What has happened to Steve Gould's "Punk EEK" revelation that the
> > fossil
> > record shows that when a new animal type shows up, it continues
> > essentialy
> > simple descent for a few million years, and then goes extinct, without
> > showing Darwinian gradual change. I remember he took hits from some
> > big
> > time professsionals, for this revelation.

As Keith noted, punctuated patterns do not occur in every example,
though they are common enough. In fact, theoretical evolutionary
studies suggest that punctuated patterns are expected in more
difficult circumstances whereas gradualistic patterns are expected
when things are relatively easy from the viewpoint of the organism in
question. If selective pressure is higher, then deviations from the
norm are more likely to be significantly disadvantageous. If the
going is easy, variants are more likely to be able to manage OK.
Under changing environmental conditions, however, eventually the old
norm will probably fall out of favor, making a quick shift to
something new desirable.

Another mistaken impression related to punctuated equilibrium is the
idea that it is "without showing Darwinian gradual change". In
reality, several of the original examples cited feature both extended
periods with no significant change followed by very rapid shift
observed in a particular population (which ended up getting preserved
as fossils) to the new state. Thus, transitions are known and do
occur in punctuated equilibrium-it's not an attempt to cover for lack
of transitions but rather suggests that transitions may be relatively
rapid, interspersed with extensive times when there's not much change.

As a high school student, I examined the lineages of two clam species,
the sunray venus and the calico clam. The sunray venus showed gradual
change, with geographic and temporal variation tending from more
circular (old/northern) to more elongate. The calico clam showed
hardly any change over the sampled interval.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.
Received on Fri Aug 24 12:18:59 2007

This archive was generated by hypermail 2.1.8 : Fri Aug 24 2007 - 12:18:59 EDT