The Homininae comprise all hominids that arose after the subfamily Ponginae (orangutans} split from the line of the great apes.

[Note 1] Until 1970, the family (and term) Hominidae meant humans only; the non-human great apes were assigned to the then-family Pongidae.

[3] Later discoveries led to revised classifications, with the great apes then united with humans (now in subfamily Homininae)[4] as members of family Hominidae[5] By 1990, it was recognized that gorillas and chimpanzees are more closely related to humans than they are to orangutans, leading to their (gorillas' and chimpanzees') placement in subfamily Homininae as well.

The Late Miocene fossil Nakalipithecus nakayamai, described in 2007, is a basal member of this clade, as is, perhaps, its contemporary Ouranopithecus; that is, they are not assignable to any of the three extant branches.

Their existence suggests that the Homininae tribes diverged not earlier than about 8 million years ago (see Human evolutionary genetics).

Today, chimpanzees and gorillas live in tropical forests with acid soils that rarely preserve fossils.

[11][12] Its separation into Gorillini and Hominini (the "gorilla–human last common ancestor", GHLCA) is estimated to have occurred at about 8 to 10 million years ago (TGHLCA) during the late Miocene, close to the age of Nakalipithecus nakayamai.

Darwin himself believed that larger brains in humans made an upright gait necessary, but had no hypothesis for how the mechanism evolved.

This theory hypothesized that hominins became bipedalists due to the environment of the Savanna such as the tall grass and dry climate.

Anthropologist Owen Lovejoy has suggested that bipedalism was a result of sexual dimorphism in efforts to help with the collecting of food.

While females groomed and cared for their children with the family group, males ranged to seek food and returned bipadally with full arms.

[citation needed] In spite of their smaller brain, there is evidence that H. floresiensis used fire and made stone tools at least as sophisticated as those of their proposed ancestors H.

Testis and penis size seems to be related to family structure: monogamy or promiscuity, or harem, in humans, chimpanzees or gorillas, respectively.