Our hands and shoulder hinge arose during an existence in trees of our ancestors.

 A squirrel-like insectivore went to life in the trees 56 million years ago. He developed fingers and thumb to grab to the branches. His hands then could keep his balance so well that he did not need a tail anymore but that was as far as only 18 million years ago.

Then he went to suspend from the branches to move yet more agile by the canopies. Thus was born our shoulder hinge that allows us to lift our arms above the head. No one other animal is able to do that, this was 6 million years ago.

Col 4