I've sorta followed research into AI on and off over the years. Early attempts to make a walking robot required at least four legs, preferably six, so that it was stable when one foot was off the ground. But humans are nothing if not persistent and someone came up with a way for a two-legged robot to walk, provided it constantly and carefully rebalanced itself in the process. Then they realized that natural walking is a process of continuous controlled rebalancing. IOW, a walker is constantly falling and recovering by putting the next foot on the ground.

Wade.