A collage of four breeds of pigeons shows two with scaled feet (top) and two with feathered feet, known as muffs (bottom). Top left is a racing homer. Top right is an English Pouter. Bottom left is an Indian fantail. Bottom right is a fairy swallow. Biologists at the University of Utah have shown how foot feathers develop in pigeon breeds in which a hindlimb development gene becomes less active and a forelimb or wing development gene becomes more active in the legs.