<P> It is among the cladists that Occam's razor is to be found, although their term for it is cladistic parsimony . Cladistic parsimony (or maximum parsimony) is a method of phylogenetic inference in the construction of types of phylogenetic trees (more specifically, cladograms). Cladograms are branching, tree - like structures used to represent hypotheses of relative degree of relationship, based on shared, derived character states . Cladistic parsimony is used to select as the preferred hypothesis of relationships the cladogram that requires the fewest implied character state transformations . Critics of the cladistic approach often observe that for some types of tree, parsimony consistently produces the wrong results, regardless of how much data is collected (this is called statistical inconsistency, or long branch attraction). However, this criticism is also potentially true for any type of phylogenetic inference, unless the model used to estimate the tree reflects the way that evolution actually happened . Because this information is not empirically accessible, the criticism of statistical inconsistency against parsimony holds no force . For a book - length treatment of cladistic parsimony, see Elliott Sober's Reconstructing the Past: Parsimony, Evolution, and Inference (1988). For a discussion of both uses of Occam's razor in biology, see Sober's article "Let's Razor Ockham's Razor" (1990). </P> <P> Other methods for inferring evolutionary relationships use parsimony in a more traditional way . Likelihood methods for phylogeny use parsimony as they do for all likelihood tests, with hypotheses requiring few differing parameters (i.e., numbers of different rates of character change or different frequencies of character state transitions) being treated as null hypotheses relative to hypotheses requiring many differing parameters . Thus, complex hypotheses must predict data much better than do simple hypotheses before researchers reject the simple hypotheses . Recent advances employ information theory, a close cousin of likelihood, which uses Occam's razor in the same way . </P> <P> Francis Crick has commented on potential limitations of Occam's razor in biology . He advances the argument that because biological systems are the products of (an ongoing) natural selection, the mechanisms are not necessarily optimal in an obvious sense . He cautions: "While Ockham's razor is a useful tool in the physical sciences, it can be a very dangerous implement in biology . It is thus very rash to use simplicity and elegance as a guide in biological research ." </P> <P> In biogeography, parsimony is used to infer ancient migrations of species or populations by observing the geographic distribution and relationships of existing organisms . Given the phylogenetic tree, ancestral migrations are inferred to be those that require the minimum amount of total movement . </P>

The simple solution is usually the right one