Why our earliest ancestors walked upright? The truth revealed:
Our earliest ancestors changed from tree dwelling quadrupeds to upright bipeds capable of walking and scrambling and the authors in Antiquity (‘Complex Topography and Human Evolution: the Missing Link’) say our upright gait may have its origins in the rugged landscape of East and South Africa, which was shaped during the Pliocene epoch by volcanoes and shifting tectonic plates.
Yes, well we have already steamed through a variety of other causes such as, we learned to walk upright so we could hit each other. Or carry infants. Or scarce resources. Or save energy. Or cool down.
It’s not really a question about function, it’s a question about how the idea of using hands got started.