A shoe is an item of footwear evolved at first to protect the human foot and later, additionally, as an item of decoration in itself. The foot contains more bones than any other single part of the body, and has evolved over hundreds of thousands of years in relation to vastly varied terrain and climatic conditions. Together with the proprioceptive system, it is what makes possible balance and ambulation. Shoes have traditionally been made from leather, wood or canvas, but are increasingly made from rubber, plastics, and other petrochemical-derived materials. The earliest designs were simple affairs, often mere “foot bags” of leather to protect the feet from rocks, debris, and cold. Since a shoe uses more leather than a sandal, their use was more common amongst people in cold climates. By the Middle Ages, turn-shoes had been developed with toggled flaps or drawstrings to tighten the leather around the foot for a better fit.