new info on old evolutionary threads-origin of phyla and chaos

David Campbell (
Mon, 9 Nov 1998 18:12:56 -0400

patterns. I now have a reprint of an article and some abstracts on the
range of physical forms feasible for animal evolution by Roger D. K.
Thomas. The article, co-authored with W. E. Reif, is from Evolution, v.
47, no. 2, p. 341-360. In it, they use geometric and construction rules to
derive a range of potential skeletal designs and check to see what range of
these are represented by modern or fossil organisms. According to one of
the abstracts (Palaeontological Association, 1997, 41st annual meeting), 83
percent of the design elements known from any organisms had already
appeared by the time of the Burgess Shale. This suggests that few novel
body plans may have been left as options for potential new phyla.

At the Geological Society of America meeting two weeks ago, there was one
talk (by Graham Budd) arguing that animal phyla have appeared at scattered
times throughout the Phaerozoic. However, this was based on semantic
issues rather than new evidence. He defined phyla as only including the
crown group (i.e., the last common ancestor of all modern forms and all of
its descendants). This means that older species are not assigned to any

On the possibly fractal nature of evolution, two talks looked at the
pattern of extinction over time (Sepkoski's data showing number of known
marine invertebrate genera by stages).
The first, for which I do not remeber the speaker's name, showed that a
particular fractal pattern did not match the pattern of extinction over
time. Although a published paper claimed to find this fractal patern in
the extinction curve, this resulted from their method of extrapolation and
not from the data.

Another paper (Roy Plotnick) argued that the pattern of extinction was a
multifractal, which is a function that is based on multiple fractal
functions. (My use of the mathematical terms may not be quite right.) He
showed that there is a similarity between the extinction curve and
multifractals, though I was not convinced that many other possibilites were
ruled out.

To me, a multifractal pattern sounds like one way in which God could have
made a deterministic system that still appears unpredictable to us.