a question about assymetrical trees

[Gijs Grob]

Many cladograms that are shown in articles and presentations seem to be
highly asymmetrical. That is, very often out of two branches only one is
splitting into two, and only one of these is splitting etc. Thus everytime
there seems to be a "chosen" branch which may radiate, while the other
branch stays constant. This leads to a succesion of paraphyletic branches.
I hope you can visualize and recognize this type of trees (I wish I could
draw it for you). I can't imagine evolution working this way. So here is my
question: could anybody tell me what may be the cause of these trees. Do
the tree producing programs prefer this type of asymmetrical trees or is
something else going on?

Gijs

___________________________
Gijs Grob
Ph.D-student
Rijksherbarium/Hortus Botanicus
Leiden University
P. O. Box 9514, 2300 RA, Leiden
The Netherlands
Tel: (+31-71) 5273583
Fax: (+31-71) 5273511
Grob at nhn.leidenuniv.nl