The Hominidae probably originated in Africa sometime between 14 my and 4 my ago. Unfortunately the fossil evidence from this time period and region is relatively poor. We regard only 11 specimens as unambiguous hominoids, and none preserves a great amount of anatomy. They come from a very restricted geographical region. Two are from Ethiopia and the rest from Kenya, where most have been found in the Tugen Hills succession west of Lake Baringo. No unequivocal fossil evidence of ancestral Gorilla or Pan has yet been recognised. The oldest hominid yet known—in the sense used here—probably dates to greater than 5.6 my. One especially interesting question in the paleobiology of the hominoidea, as in other taxa, is the relation of extrinsic factors to speciation. To resolve this issue, diagnostic and well-dated specimens are necessary. However, they need not be anatomically spectacular. Fragmentary specimens, although imperfect anatomically, can be just as effective as more complete material in defining taxonomic branching points. The origin of Hominidae, or at least bipedalism, has been conjecturally associated with a regional environmental change from tropical forest to widespread grassland. Evidence accumulating from various parts of Africa, particularly the Tugen Hills, suggests this was not an abrupt transition. The pattern of habitats was probably patchy in space and time. This may have been a factor in the origin and development of the hominid clade. Much progress has recently been made, but further hominoid specimens, coupled with environmental information from well-calibrated sequences, is necessary to elucidate the nature and causes of cladistic branching within the superfamily.