During the period in which australopithecines was evolving in these two crucial respects, the Homo genus appeared. Homo diverged from the australopithecines around two million years ago, and interestingly enough, tools began to appear in the fossil record around this time. The appearance of these stone tools signals the beginning of the Paleolithic era. This Stone Age covers almost all of human history, but is predated by nearly 3,900 million years of evolution.
Several species of Homo, all but one of which are now extinct, evolved in various locations.
Homo habilis, the first species of Homo, lived between 2.4 to 1.4 million years ago, evolving in south and east Africa. Homo habilis is the first human species to be associated with the use of tools.
Homo rudolfensis and Homo georgicus are two species which lived between 1.9 and 1.6 million years ago, about which is known very little. It has been suggested that these may be species of habilis.
Homo erectus appeared between 1.5 and 1 million years ago, and from its origins in Africa migrated to Europe and Asia. During this time, Homo habilis living in some locations began to evolve larger brains, and to make and use more sophisticated stone tools. On the basis of these and other differences between the two, erectus was determined to be a separate species. Its locking knees and the placement of its foramen magnum (the location where the spine meets the skill) allowed Homo erectus to walk fully upright. Homo erectus may have used fire to cook meat.
Homo heidelbergensis lived between 800,000 to 300,000 years ago. Also known as Heidelbuerg Man, this species is believed to be an ancestor of Homo neanderthalensis.
Homo neanderthalensis appeared around 250,000 and became extinct fairly recently, somewhere between 25,000 and 30,000 years ago. While there has been considerable debate over the evolutionary relationship between neanderthalensis and sapiens, new mitochondrial DNA evidence indicates the two were a separate species with a common ancestor which lived around 600,000 years ago.
Homo floresiensis lived between 100,000 and 12,000 years ago, and has been nicknamed “hobbit" due to its small size. Floresiensis is particularly interesting because it represents an example of a Homo species taking a distinct and separate evolutionary path. The species has several traits in common with modern humans, but the most complete floresiensis fossil is just one meter high. However, it has also been theorized that floresiensis was not a separate Homo species, but in fact a sapiens which had suffered from dwarfism.
The first Homo sapiens appeared on the scene somewhere between 400,000 and 250,000 years ago, evolving from Homo erectus. Eventually, this new species would replace all other existing human species, and Homo sapiens is the only species of human still in existence. There are two theories to account for how this happened—the first says that Homo sapiens first evolved in Africa, then migrated to other locations and replaced populations of other human species, while the other argues that modern humans evolved from existing Homo species in multiple locations.
So far, there is not a sufficient amount of fossil evidence to prove or disprove either theory; however the “Out of Africa" model, in which sapiens evolved in Africa and migrated to replace human populations in other locations, is favored.