Because "P. boisei" and "P. aethiopicus" are both known from East Africa and "P. aethiopicus" is only confidently identified from the skull KNM WT 17000 and a few jaws and isolated teeth, it is debated if "P. aethiopicus" should be subsumed under "P. boisei" or if the differences stemming from archaicness justifies species distinction. The terms "P. boisei" sensu lato ("in the broad sense") and "P. boisei" sensu stricto ("in the strict sense") can be used to respectively include and exclude "P. aethiopicus" from "P. boisei" when discussing the lineage as a whole.