Han Dynasty @ National Geographic Magazine: "Many of us recognize the black-and-white circular yin and yang symbol. But where does it come from? And what is the philosophy behind it? The roots of this philosophy grew in ancient China around the third century B.C. as an attempt to explain the cyclical nature of the universe. During the Han dynasty many people believed that a single principle, composed of two opposing forces, yin and yang, compelled change in the world.
Yin does not exist without yang. Each completes the other. Yin represents the dark, passive, female principle, and yang the light, active, male principle. Alternating pressures of yin and yang exist in a harmonious balance, like the waxing and waning of the moon, or the ebb and flow of the tide. Life and death can be explained as an unceasing cycle, just like seasonal plants flower, decay, and enrich the soil for future plants and trees.
The Han wanted to make philosophical sense of the natural world. At some point yin and yang cosmology blended with another school of thought, which viewed the world in terms of five distinct elements. These five elements-metal, wood, water, fire, and
earth-represented the five forces of the natural world. It was thought that the alternate pressures of yin and yang occur within these five stages. The Han tried to understand change in the physical and celestial worlds so they could better explain reversals in the human world.
Yin and yang philosophy still permeates Chinese thought today in areas like astrology, literature, art, and medicine.