The early discoveries of early hominid fossils were made at Olduvai Gorge, by the Leakeys. Not long after Mary Leakey had found Australopithecus boisei, Louis Leakey found found fossils which he thought were the makers of the stone tools found in the gorge. At first he had attributed Australopithecus boisei with the stone artifacts discovered in the gorge, but when the hominid fossils were finally found, he immediately realised that this was not the case.

The fossils were thought to be slightly older than Australopithecus boisei (about 1.75 million years) and in addition, the teeth were smaller and the brain was calculated to be significantly larger. Louis Leakey became convinced that these fossils were in fact the ancestors of modern humans. It was determined that Homo habilis (as the fossils were named) overlapped with the robust australopithecines for roughly 1 million years. Homo habilis means "handy man" and was suggested to them by Raymond Dart.

| Ardipithecus ramidus | Australopithecus anamensis | Australopithecus afarensis |
| Australopithecus africanus | Australopithecus aethiopicus | Australopithecus boisei |
| Australopithecus robustus | Homo habilis | Homo rudolfensis | Homo erectus | Homo ergaster |
| Homo heidelbergensis | Homo neanderthalensis | Homo sapiens |