KNM ER 23000 is thought to represent a male early human of the species Paranthropus boisei. Only the top portion of the skull is preserved in ER 23000. However, sceintists can infer the the gender of this individual from the more pronounced features of the skull, for example the large browridges (middle and bottom photographs) and the sagittal crest (top photograph). In other ape species, especially in gorillas to which humans are closely related, prominent features such as these are typically associated with males, while more gracile features are indicative of females. Compare the view of the sagittal crest in ER 23000 to the that of supposed female P. boisei KNM ER 732.

The base of the wide flaring zygomatic arches typical of P. boisei can be seen on the left side of the skull.