Taxonomy with confidence

There are essentially three ways in which four species may be related in a phylogenetic tree graph. It is usual to compute for each of these three possibilities the smallest number of mutations that could have brought about the observed distribution of characteristics among the four species. The graph that minimizes this number is then preferred. In fact, the hypothesis that the graph chosen in this way is correct may be accepted with confidence if the minimum is strong in a sense described here. In principle, the theory could be extended to treat sets of more than four species.