A couple of days ago I sent out an email that referred to a paper by Stephen
Jay Gould, the American paleontologist. I had found one of the things the
paper said rather mind-bending:
"... the subsequent history of animal life amounts to little more than
variations on anatomical themes established during the Cambrian explosion
within five million years. Three billion years of unicellularity, followed by
five million years of intense creativity and then capped by more than 500
million years of variation on set anatomical themes can scarcely be read as a
predictable, inexorable or continuous trend toward progress or increasing
complexity."
So I developed a message in which I speculated on how secure our place in
evolution might really be. Digby Hunt, a friend with much more experience and
a more thorough understanding of evolutionary research than I have sent me the
following response:
A short note. Stephen Gould was a respected but rather flamboyant
Palaeontologist but the hypothesis that evolution proceeded only in spurts has
not been accepted by many of his peers. Yes no doubt the overall rate of
evolution varied both up or down depending upon the local environments at the
time and the need to adapt to changes over time.
Gould based his suggestion that there was a Cambrian explosion of multicelled
creatures on the remarkably preserved fossils of the Burgess shale in BC. but
said those species died out. Actually he got them upside-down and in fact they
are accepted as having been some of the precursors of the varied fauna of
to-day. Also there is no evidence that there were only single celled creatures
before the so called Cambrian explosion. A creature as relatively complex as
Olenellus(A trilobite) from the lowermost Cambrian strata did not just
materialise from a single celled creature. Also indications of other creatures
have been found in pre-Cambrian rocks. It is not surprising that the
Precambrian fossil record is almost nonexistent since most strata in origin are
volcanic, intrusive or highly metamorphosed. Yes there are some relatively
unchanged sedimentary strata but hardly in their deposition likely to preserve
soft bodied creatures. I just read a paper from the last months Journal of the
Geological Society on the sedimentation of the Burgess shale explaining the
unusual circumstances that enabled soft bodied creatures to be preserved by a
film of chitin.
Finally I once did a research project on Christobella a foraminifera from
Eocene sands which were deposited over several million years and was able to
demonstrate evolutionary changes in the shell which is very similar in shape to
a Nautilus but only about 2mm in total size.
Ed
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