The problem of finding least-cost reconstructions of past host/parasit
e associations, given the phylogenetic histories of a set of host taxa
and of their associated parasites, is known to be complex. I provide
in this article a new method of implicitly listing all the potentially
optimal solutions to the problem, by considering each hypothesised pa
st association individually, in a structure I have termed a Jungle. Th
ese structures are demonstrated to enable fast acquisition of globally
optimal solutions under general weighting schemes, including minimisa
tion of total number of postulated events and maximization of postulat
ed cospeciation events. A simple example is given, and the pocket goph
er/chewing louse system investigated by Hafner and Nadler [Hafner and
Nadler, Nature 332 (1988) 258] is re-examined. (C) 1998 Elsevier Scien
ce Inc. All rights reserved.