?rule of three?

[Zdenek Skala]

The distribution of the taxa-within-taxa (species within a genus,
genera within a family...) number generally follow the "hollow"
("Willis") curve, i.e. the most frequent are monotypic genera, less
frequent genera with two species and so on to the long tail of the
genera with very-many species. This pattern is quite stable over
various taxonomic groups (and even other things like human family
names). Hence, the "average" genus does not represent some
central tendency but proportion of the large and small genera which
indeed can (and does) differ among taxonomic groups. This
differences can, in my opinion, reflect real differences in the
speciation mode etc.
Zdenek
++++++++++++++++++++++
] Zdenek Skala
] e-mail:
] skala at incoma.cz