In this paper I briefly discuss what "species" are, and how they might be recognised in the fossil record, and support a time-dependent view of higher categories (genus, family). The genus Homo, according to the time-dependent model, contains Australopithecus and Paranthropus, and perhaps Kenyanthropus, as synonyms. I suggest 19 "definite species" in the genus Homo, with several other "potential species" and "possible species".
Keywords: Family, Genus, Homo, Potential species, Species, Time-dependent model.