The issue is unresolved

The question of what the frequencies are of different patterns of evolutionary rates is still an open one.

Some, like Cheetham's bryozoans, illustrate a punctuated equilibrial pattern of evolution; others, like Sheldon's trilobites, show a pattern of phyletic gradualism.

We shall need many more such studies before a rational conclusion can be drawn.

As Simon Conway Morris explains, we shall need many more such studies before a rational conclusion can be drawn.