Outgroups

[Don.Colless at CSIRO.AU]

Zdnek Skala wrote:
Outgroup(s) is(are) used for character matrix polarization in an
"absolute way", i.e. the character states found in outgroup(s) are
believed to represent plesiomorphic states for the group in question.
Consequently, all the "homoplasy burden" is placed on the group studied.

Here, I think, and elsewhere in this thread, there's been some neglect
of the two types of tree-rooting: (a) by forming an unrooted tree and
then attaching an outgroup, and (b) by including one or more outgroups
in the original analysis. I trust I'm right in saying that the latter
allows for homoplasy in the outgroup; the former (Lundberg rooting)
doesn't. Each has its own advantages, and both are worth trying (PAUP
has - had - these options).


Don Colless,
Div of Entomology, CSIRO,
GPO Box 1700,
Canberra. 2601.
Email: don.colless at csiro.au
Tuz li munz est miens envirun