Thorne, Guiding principles of biogeography 
849 
continental masses by the breakup of West Gondwana, then evolved into those 
families now totally or largely restricted to them, as the Didieriaceae in Madagascar, 
the Aizoaceae, especially the mesembyanthemoid taxa, in Africa, and Cactaceae and 
other families in the American continents and islands (Thorne 1978). 
13. The lower the rank of a taxon under consideration, generally the more instructive 
may be its disjunct range. 
Higher categories have had so much time to disperse about the earth's surface that 
often they tell us little about the causes of their disjunctions. Disjunct species or 
genera, depending upon their degree of vagility and the prevalence of their pattern 
of disjunction, can tell us much about how and possibly when the disjunction took 
place. Among other things lower categories can be analyzed biosystematically, 
biochemically, or through molecular studies. 
14. Parsimony, which is a fashionable term for Occam's razor, though highly 
logical, is not necessarily how evolution has taken place nor how patterns of 
distribution and disjunction have developed in space and time. 
It is surely parsimonious to explain all transatlantic disjunctions by the breakup of 
West Gondwana but it is not realistic to ignore the time frame of events, the categorical 
ranks of the taxa under study, nor the spread potential of said taxa. Mother Nature 
unfortunately does not always operate on a parsimonious basis. 
15. Though often fascinating to the practioner, the techniques and procedures 
used in developing biogeographical conclusions should not become more important 
than the results achieved. 
We must avoid losing sight of the biogeographical forest because of concentration 
on procedural trees. A corollary here is that buzzwords, though impressive additions 
to our trendy vocabulary and often very helpful in obtaining substantial grants 
for our research, cannot substitute for careful accumulation and synthesis of 
biogeographical information, inductive reasoning, and application of prudent good 
judgment in our efforts. 
Conclusion 
The principles just discussed should show that the division of biogeographers 
into 'dispersalists' and 'vicariantists' is not only artificial and arbitrary, but 
counterproductive for our science. We should appreciate the efforts of our peers and 
dispense with fanciful hypotheses and polemics. Vicariance biogeography has new 
ideas and new techniques to offer that can be useful to all of us. At the same time, 
there is no need to empty our biogeographic tool-chest just to accept one more new, 
shiny, useful tool. The chest is a big one with plenty of room for many more useful 
tools, including cladistics and molecular taxonomy. 
References 
Balgooy, M.MJ.van. (1971) Plant-geography of the Pacific. Blumea Suppl. 6: 1-222. 
Barker, W. R. (1986) Biogeography and evolution in Euphrasia (Scrophulariaceae), particularly 
relating to Australasia. Pp. 489-510 in B.A. Barlow (ed.), Flora and Fauna of Alpine Australasia: 
ages and origins (CSIRO Australia: Leiden). 
Barlow, B. A. & Schodde, R. (1993) Bird dispersal of loranthaceous mistletoes to remote Pacific 
islands: symbiosis in default. Beaufortia 43: 124-129. 
