The traditional theory believes that due to climate change, human ancestors were forced to leave the arboreal environment and chose to walk upright on the ground. A recent study believes that early humans walked upright in the rugged mountainous regions of eastern and southern Africa today. The terrain was formed by volcanic eruptions and tectonic plate movements during the Pliocene. Human ancestors were attracted by rocky terrain and canyons. They can provide a good sheltered habitat and give them the opportunity to trap prey. This environment required early humans to have the ability to walk and climb upright
human ancestors eventually evolved to walk upright on two legs.
Human ancestors chose to walk upright to better adapt to the terrain.