It seems definite that Gould overestimated the contingency, as more and
more of the weird early Paleozoic taxa are found to fit into known higher
taxa, albeit by somewhat expanding our ideas of the defining features of
the higher groups. Convergent evolution likewise points to some degree of
environmental constraint. However, there remains a wide range of views on
the degree of constraint. From my Calvinist perspective, I believe that
the process was very tightly constrained. However, the constraint could be
"built in" from the creation of the universe, or slightly more
"interventionist" with the course of "naturally" indeterminate events being
caused as they come to pass (e.g., which radioactive atom decays first).
David Campbell