This identification was, however, problematic given that its large post-canine teeth and other robust facial features are usually indicative of a male. Proper gender identification did not come until 1972, when John Wallace of the University of Witwatersrand associated the STS 71 cranium with the STS 36 mandible found in the same geologic layer. This identification was made by exactly matching the wear patterns of the teeth on the two specimens. Based on the size of its teeth, the STS 36 mandible had already been determined to be male. Thus, STS 71 was a male.

STS 71 offers some problems for paleoanthropologists, as it is male, and has a cranial capacity estimated at only 428cc. (But see the What's Hot! 1998 article #1 on cranial capacities of A. africanus individuals.) Also the face is less prognathic than the supposed female STS 5 skull. This causes problems because primate sexual dimorphism tends to produce larger males than females, and features such as prognathism among African apes tend to be more pronounced in males than females. If the identification of STS 5 as female is correct some researchers conclude that this may mean there are several species of early human at Sterkfontein in this time period.