What did Newton understand that was such a revolution? Can someone just... explain gravity to me? Let's start with a ...

Like humans today, they maintained good balance because their center of gravity moved forward in a ... were the parts of a knee joint. Like a human knee, it could "lock," allowing its owner ...

in order to move their center of gravity over whichever leg is bearing their weight. Human bodies have a number of other adaptations to walking upright, as well. Our foot is specialized as a ...