Origins of Yin Yang
Yin and yang was first conceived through patient observation of the forces of nature. The Taoists who developed the system of traditional Chinese medicine saw the universe as a unified field, constantly moving and changing while maintaining its oneness.
This constant state of change was explained through the theory of yin and yang, which appeared in written form around 700 B.C. in the I Ching ("Book of Changes").
According to the theory, nature expresses itself in an endless cycle of polar opposites such as day and night, moisture and dryness, heat and cold, and activity and rest.
Yin phenomena are those that exhibit the nurturing qualities of darkness, rest, moisture, cold, and structure. Its Chinese character depicts the shady side of a hill.
Yang phenomena have qualities of energy such as light, activity, dryness, heat, and function. Its Chinese character represents the sunny side of a hill.
Everything in nature exhibits varying combinations of both yin and yang. For example, the morning fog (yin) is dissipated by the heat of the sun (yang); the forest fire (yang) is extinguished by the rainstorm (yin); the darkness of night (yin) is replaced by the light of day (yang). Any phenomenon within nature can be understood in relation to another; one will always be yin or yang in comparison with the other.
Everything in nature can be expressed as the opposition of yin and yang. This is the energizing force of all aspects of nature. It is dynamic and the basic foundation for change in nature.
Yin and yang are also relative terms: A forest fire is more yang than a campfire; a campfire is more yang than a spark. Nothing is purely yin or yang; it is always a matter of comparison.
Yin and yang are interdependent. Even though yin and yang are opposites, one has no meaning without the other. For example, day would have no meaning without night; heat cannot be understood without knowing what cold feels like; fever and chills can't be determined without experiencing the normal body temperature.
Yin creates yang; yang creates yin. Numerous examples of this principle can be seen in nature. For example, on a hot summer day (yang), there is a sudden thunderstorm (yin). A person may get symptoms of chills and a runny nose (yin) that turn into a fever with a sore throat (yang). A hyperactive child runs around frantically (yang), then suddenly falls asleep (yin).
Yin and yang mutually control each other. This is the basic mechanism of balance in nature and the human body. When the body gets overheated from exercise, the pores open and sweating lowers the temperature. When the body gets too cold due to exposure, the muscles shiver to generate heat.