Thank you for your review of the changes that took place in the
You provided evidence that 1) precursors to the Cambrian animals have been
found, and 2) some evidence that the Cambrian explosion was not sudden or
You overinterpret the data when you say that the "appearance which is now
known to be a very gradual appearance of more and more complex animal life
forms extending from 700 million years ago to 500 million years." By this
interpretation, the Cambrian explosion is a non-event.
Others disagree. You haven't dealt with Bowring et. al.'s (Science, 261,
Sept. 3, 1993) estimate that the Cambrian explosion lasted at most 10 million
years and as little as 5 million.
Gould called the event an "overt evolutionary burst to large size and greatly
increased anatomical variety in the subsequent Cambrian explosion" (Natural
Moreover he said,: "The Cambrian explosion ranks as such a definitive
episode in the history of animals..." and then goes on to acknowledge the
need to understand antecedents and the unfolding of this cardinal geological
These views hardly sound like a very gradual appearance of more and more
complex animals, as you described it.
The question I raise is that mechanism was involved.
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