If the
>book is up to date, it probably will discuss why the Cambrian explosion
>happened; if very up to date (highly unlikely that this has made it into
>textbooks), it will mention the increasing evidence that it extends well
>back into the Precambrian and was less explosive than has been thought.
Some perspective from an article in Time magazine (When life exploded,
TIME, 12/5/95
http://ucaswww.mcm.uc.edu/geology/huff/When_Life_Exploded.html). The
article pointed out that all animal phyla except perhaps bryozoa are
present in early Cambrian, and that they all appear within a very small
slice of time ("no more than 10 million years")
Steven Gould "Fast is now a lot faster than we thought, and that's
extraordinarily interesting"
Samuel a Bowring: "We now know how fast fast is, and what I like to ask my
biologist friends is, How fast can evolution get before they start feeling
uncomfortable?"
Rudolph Raff: "There must be limits to change. After all we've had these
same old body plans for half a billion years."
G. M. Narbonne, Queens U. (paleontologist): "What Darwin deescribed in the
Origin of Species was the steady background kind of evolution. But there
also seems to be a non-Darwinian kind of evolution that functions over
extremely short time periods--and that's where all the action is."