The primates appeared during the Tertiary period, and by the end of the Tertiary there is evidence of upright bipedalism, shown by this Homo erectus skeleton, who died at about 10 years of age. The ability to stand on two feet brings several advantages:

• Looking
Extra height to peer over the tall grasses on the African plains.

• Signalling
Hand movements are an important signalling device (witness a Gorilla beating its chest!)

• Carrying
Taking young to a safe place or gathering food to store and eat later.

• Throwing
Stones may be thrown to scare off predators.