>The author's stated:
>
>"To evaluate and supplement the available data on cell type numbers within
>clades, of which Sneaths's has proven to be the most consistent with modern
>ultrastructural studies, somatic cell type numbers were tallied from the
>literature for those organisms for which reasonably complete histological
>descriptions exist." James W. VAlentine, Allen G. Collins, and C. Porter
>Meyer, "Morphological Complexity Increase in Metazoans," Paleontology
>20(1994):2:131-142, p. 133
>
>Your objection doesn't take that into account. And once again, to all the
>naysayers, what measure of complexity would satisfy you? If not cell type
>number then what? All I hear on that score is silence.
I applaud any attempt to deal with the evolution of complexity that makes
sense; this attempt does make sense in its basic concept, in that it uses a
definition of complexity which is limited to something quantifiable, namely,
'number of cell-types'.
But I question the implication that this is going to really satisfy our wish
to understand evolution in general. 'Complexity in general' is not
quantifiable, so it's not a scientific term. No specific quantifiable measure
of complexity is going to be satisfying.
The article implies gradual simple-to-complex evolution, an old-fashioned
idea. Evolution through loss is not recognized, nor is the suddenness of the
origin of vertebrates. Major phylogenetic assumptions are implied without
justification.
Morton wrote to Mike:
>The agnatha were estimated to have had only 64 cell types--their descendants,
>man, has around 210. And since we humans are among the most complex of
>beings on the surface of the earth, and we just recently evolved, it further
>supports the concept that complexity has increased over time.
How do you know the agnatha were the progenitors of other vertebrates?
This is something that was taken as obvious by the first evolutionists; but
what findings since then support the assumption? The major phyla came
into being in a trice. Given the reductive pattern of subsequent skeletal
evolution, the agnatha may well have evolved from gnathostomes.
The evidence is far too fragmentary to claim knowledge of specific
genealogy here.
If you count cultural evolution, which has nothing to do with cell-types,
perhaps man is "the most complex of beings on the surface of the earth".
But by any other yardstick I don't see where we have greater complexity
than other animals. Do we have electric organs? Spines? Peacock feathers?
Brains anywhere near the size of elephants' or whales'? In none of our
perceptive organs are we the champions of the world. etc etc.
I strongly suspect that the figure for number of cell types in humans vs,
for example, aves, is skewed by the much greater study we've given to
human physiology.
It would be interesting to see a detailed tabulation of these cell types
and their supposed times of appearance in evolutionary history--an
evolutionary chart showing not animals but cell types. I suspect that
the implications of such a detailed chart would not support Morton's
implications about phylogeny. It would show that the later cell types
are trivial additions, if they are in fact later additions at all. It would
show that the Cambrian explosion was the evolutionary marvel, not
the subsequent events.
--Cliff Lundberg ~ San Francisco ~ cliff@noe.com