Selaginaceae are not beyond evolutionary examination

[S W Graham]

It is safe to assume that ligules cost a significant amount of energy to
make. If they do not serve SOME adaptive function or other, it is unlikely
that they would persist as vestigial structures over a substantial period of
time, whatever the story was behind their evolutionary origin.

Those mutations that remove structures with no fitness consequences are not
selected against.  So we can safely predict the eventual loss of structures
with no current adaptive value.  Given the constant mutational pressure that
organisms are subject to, what is vestigial now won't be for long: Inertia
will only keep a character around for so long.  Unless it really isn't
vestigial.

We do not need to know "why" a structure such as the ligule in
Selaginellaceae evolved, to know that its maintenance across such a long
time-frame signifies one (or more) functions.  Nor do we necessarily need to
use cladistic methodology to study its current functional significance,
although this can provide valuable insights into its original role.

This is not a matter of "personal faith".  Like the rest of science it is an
empirically testable hypothesis.  If a trait persists, the onus is on the
skeptic to disprove a functional role.

Sean Graham
___________
Dept. of Biological Sciences
University of Alberta
Edmonton, Alberta
CANADA T6G 2E9

(780) 492-7567