Once upon a time there was a race of bipedal creatures. They ran around all over the place, meeting, exploring, finding food, going hungry, hurting themselves and each other, taking care of themselves and each other, and gazing at the stars.
These creatures had an unusual sort of anatomical feature: their two legs needed different types of food. Many foods could nourish their whole body, including both legs, but some types of food were only good for the left leg, some for the right. So, as a result of this, most of the creatures had one leg longer than the other and they walked about in a sort of lurching way. They did their best to find foods for both legs.