Felsenstein notes (2004:145):
"Many systematists believe that it is important to label certain methods (primarily parsimony methods) as 'cladistic' and others (distance matrix methods, for example) as 'phenetic'."Why does Felsenstein reduce the theory of cladistics and phenetics to different types of method? Part of the reason is that Felsenstein wishes to grant equal time to all quantitative (numerical) methodologies. Unwittingly (perhaps), he makes phylogenetics a 'realist' agenda for numerical systematics - rather than 'phenetic', a term carefully avoided.
Methods to one side, Felsenstein sees no purpose in discussions of classification, noting that,
"I would say that the effort put into this controversy is further evidence that systematists do not have their priorities straight. In their day-to-day work they really do not make much use of classifications, but they show a strange obsession with fighting about them for reasons that seem to me to be an historical curiosity" (Felsenstein 2005)Felsenstein's dismissal of classification should not be surprising. Homology and monophyletic groups, crucial to the enterprise of classification, are not necessary under phenetics (in fact, Felsenstein mentions neither homology nor monophyly in his book) (see Williams & Ebach 2005).
So, what, exactly is phenetics? Or what has it become?
Phenetics is more than just a method of grouping by overall similarity; it's more than just a method. It's way to not do (to avoid) classification, namely to group taxa without any notion of homology beyond mere similarity, to form arbitrary groups without any notion of relationship (paraphyly) and work comfortably with branching diagrams depicting similarity without any specified hierarchy (unrooted trees). Phenetics is a synthesis that unites various numerical procedures to find non-groups that stem from ancestral 'vices' in a world in which the taxonomist and systematist has no prior knowledge or conviction of classification.
Perhaps there is a broader question: What are the fundamental differences between the Modern Synthesis, numerical phylogenetics, numerical taxonomy and phenetics? We know of none; all are based on simple similarity.
Felsenstein, J. 2004. Inferring Phylogenies. Sinauer Associates Inc., Massachusetts.
Sokal, R.R., Sneath, P.H.A. 1963. Principles of Numerical Taxonomy. W.H. Freeman, San Francisco.
Williams, D.M., Ebach, M.C. 2005. Drowning by Numbers: Re-reading Nelson's Nullius in Verba. Botanical Review 72, 355-387.