Families and punctuated equlibria

[Finn N. Rasmussen]

Didn't the theory of "punctutated equilibria" recognize families and
other higher categories as units of evolution? Take a look at the "real
and random clades" in Gould, Raup, Sepkoski, Schopf and Simberloff: "The
shape of evolution : a comparison of real and random clades",
Paleontology 3: 23-40 (1977), also included as fig. 6.13 (p. 300) in
Eldredge and Cracraft: phylogenetic patterns and the evolutionary
process" (1980). The socalled clades are orders of brachiopods. Several
of "clades" shown are actually paraphyletic  groups in the usual
cladistic sense, but evidently the authors imagine that orders can spawn
other orders by some higher level branching process - an "ordination",
like a speciation.

One may wonder how ardent cladists like Eldredge and Cracraft could
accept this, but I think puncutalists actually believed that many
evolutionary processes worked at distinct natural hierarchic levels.
This view seems to have disappeared, but it could be transferred to a
quite different level and yet be true in some sense: consider the
spindle-shaped "clades" as cladograms of all cells in multicellular
organism, that occasionally releases gametes (or, better,  asexual
monads). Eventually, the number of descendant lineages from the original
founding cell become very few and die out, causing the histo/cladogram
to become spindle-shaped. Meanwhile, some of the spores have established
new spindles...

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Finn N Rasmussen
Botanical Institute, University of Copenhagen
e-mail: FinnR at bot.ku.dk
web: www.bot.ku.dk