Getting upright on two feet (Toumai) started the journey 6 million years ago in ancient African jungle
The ability of Grasping with feet was something we lost but our ancestors had had ( like our relatives chimpanzees who are really Climbers)
Climate changed the environment: from jungles to woodland. Standing upright was great advantage to get the fruits which were in higher parts
Walking is a physical skill that should be learnt. (Like babies, some of are slow some are fast learners) they began using bones and muscles differently
3 million years ago Africa began drying. Whole new world: savannah! There were 6 different Walking apes.
In the open savannah to survive it was the ability of running that made one particular specie to continue evolving.
Nariokotome boy dated back to 2 million years who could run long distances was our ancestor.
Keeping cool was critical in the hot environment. Our ancestors developed something effective: they lost ape like hair
It took almost 4 million years from Toumai to Nariokotome boy. Our hands were freed now. A chimpanzee can not eat a fruit by one hand! Our thumbs are longer, our little fingers can make more pressure. Not making stone tools but it was cutting meat with a tool that made our thumbs longer. So not only changing environmental conditions but also the way we use our body transformed our bodies.
We are no climbers with short legs but walkers, runners with longer legs and tool makers.