The key question concerning the phylogenetic relationships of the robust australopiths is whether they are monophyletic or polyphyletic. Recent cladisticCladistics analyses consistently support a hypothesis of Paranthropus monophylyMonophyly owing to the large number of craniodental characters that seemingly are synapomorphies of the group. However, some workers have suggested that the strength of this evidence is overstated because many traits are either morphologically integrated, prone to homoplasyHomoplasy because they share a common function, or because seemingly similar character states lack a common developmental basis and may not be homologous. Any of these possibilities, if true, would weaken the case for Paranthropus monophyly. On the other handHand, only three characters have been used to argue for Paranthropus polyphylyPolyphyly, and each has been questioned. Given this, we contend that Paranthropus monophylyMonophyly should be adopted as the most viable working hypothesis until more characters can be found suggesting that the eastern and southern African robust lineages evolved independently from different ancestors.