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The evolutionary process shapes species by replication, variation, and selection, leading to adaptation.
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Humans are one of roughly 200 species of the Primate order, a biological group that's been evolving for about 60 million years.
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Hominids appear (only in Africa) by at least 4 million years ago with the following adaptive characteristics: bipedalism (habitually walking on two legs), encephalization (larger brains than expected for their body size), small teeth (smaller teeth than expected for their body size — the canines in particular).
| Hominid Group, Diet, and Tool Use | Some Genera and Species Included | Fossil Finds | Dates | Evolutionary Fate |
|---|---|---|---|---|
| Gracile australopithecines: omnivorous diet with little tool use | Australopithecus afarensis, Australopithecus africanus | A. afarensis in Ethiopia, and A. africanus at many sites in South and East Africa | Over 4 million years ago (A. afarensis) to about 2 million years ago (later A. africanus) | A. afarensis probably ancestral to A. africanus; A. africanus probably ancestral to early Homo |
| Robust australopithecines: more herbivorous diet with little or no tool use. | Australopithecus aethiopicus, Australopithecus robustus | A. aethiopicus and A. boisei in East Africa, A. robustus in South Africa | Over 2 million years ago (A. aethipoicus) to about 1 million years ago (late A. robustus) | Extinction around 1 million years ago |
| Early Homo: omnivorous diet with more animal tissue consumption and survival relying on tool use. | Homo habilis, Homo rudolfensis, earliest Homo erectus | Olduvai Gorge, Tanzania and Koobi Fora, Kenya | Earliest Homo around 2.5 million years ago; clearly H. erectus by 1.8 million years ago | Evolved into H. erectus by 1.8 million years ago |