It's a general problem – the algorithm does not care what you are calling the top, bottom, head or foot. It would be great if this were added to the game.
- Give it only a second or two to make the fittest the one that waddles forward. Slowly increase the simulation time.
- Splay the legs so that it starts in a relatively stable position.
Doing this, I managed to create a 2-legged walking "human" but it only managed to waddle forward very slowly – nothing like a real human gait.