We have examined the crowns of chimpanzee, australopith, and Paranthropus species and early Homo in order to investigate two different, widely recognized, dental trends in Plio-Pleistocene hominin evolution. They are a reduction in crown size and morphological complexity in Homo, and an increase in crown size and morphological complexity in Paranthropus. A phenetic assessment of maxillary and mandibular molar crown non-metrical traits revealed that two australopith species (Au. africanus and Au. afarensis) are much more similar to each other than either is to Paranthropus, and together all hominins are distinctively different from chimpanzees (P. troglodytes and P. paniscus). The difference between Paranthropus and australopith postcanine teeth was 20–30 times greater than that between the australopith species and the difference between the two australopith species was about half the difference between the two extant chimpanzee species. The characters that contribute to the increase in crown complexity seen in Paranthropus do not appear to be primitive retentions from a great ape ancestor, and there is some evidence that the same, or a very similar, trend towards trait intensification is already present in australopiths. These traits include additional cusps on the maxillary and mandibular molars, and the expanded P 4 talonid. Early Homo exhibits the primitive condition for many of the molar traits, but it has also lost many other primitive traits (upper molar anterior and posterior foveae, for example) that are present in the australopiths. Relative to Pan, and similar to the australopiths, early Homo possesses a larger P4 with a somewhat expanded talonid, but this trend is subsequently reversed in later Homo. Our study reveals that some of the dental trends said to be characteristic of Homo actually appear relatively late in human evolution.