>I remember reading somewhere the idea that evolution is "slowing down" in
>the sense that the major body plans were laid down very early, and
>diversification has been within those plans. As time progressed the
>variation became more and more restricted until we find that now not
>a great deal happens except for "trifling losses and gains at the species
>level" (I think that was the expression used - I'm not sure now if the
>statement was that it has already reached that stage, or appears to be
>headed in that sort of direction.) Is that the sort of thing that Robin
>had in mind when he posed the question? What do others think?
I offer some quotations from an article in Time magazine a while back(When
life exploded, TIME, 12/5/95
generally uncover the underbelly of the problem for evolutionary origin of
life: 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 of Harvard: (paleontologist) "Fast is now a lot faster than
we thought, and that's extraordinarily interesting"
Samuel a Bowring, M.I.T.(geologist): "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, Indiana U. (biologist): "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 described 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."
To realize just how significant these quotations are recognize that
Caenorhabditis, whose entire genome was just completed, has 40% of its
genes represented in humans. This figure is a minimum figure for the
complexity of the common ancestor of nematodes and humans, an ancestor,
that up until very recently was characterized as having almost no features,
and is, of course only hypothetical, and has no fossil representation. We
can no longer labor under the illusion that these posited ancestral forms
are just simply not preserved. We are talking deep in the Precambrian, not
about a few million years that we are playing with in China and in the
Ediacaran fauna. There are no deep Cambrian metazoan fossils. Yet this is
when all major groups of animals would have had to originate in the