A Geomedical Approach to Chinese Medicine: the origin of the yin-yang symbol

This chapter shows how to compute Yin and Yang for different latitudes so traditional Chinese herbalists can quantify the efficacy of herbal drugs. Based on daylight hours, the chapter provides a simple formula that allows computation of Yin and Yang for each day of the year. Moreover, using daily Yin and Yang values, the chapter shows how to render the Yin-Yang symbol properly in accordance with its original meaning. Considering the importance of Yin and Yang in traditional Chinese medicine (TCM), the rendering method presented in this chapter provides evidence that TCM, in its origin, is a geomedical science. Herbal medicines collected from different geographic locations can significantly differ in their therapeutic efficacy. The concentration of bioactive substances varies depending on many local factors, such as sunshine hours or chemical and physical properties of the soil. To guarantee the optimal composition of herbal drugs, Chinese herbalists use “geo-authentic” herbs from recognized locations. However, it is often difficult to confirm geographical authenticity. The lack of formal models for Yin and Yang, and herbal efficacy in general, complicates objective comparisons and evaluations. Herbalists and practitioners of TCM need a better formal understanding of the Yin-Yang composition of each herb. This chapter contributes to the solution to this problem by providing a formal description of Yin and Yang. It shows in a mathematical way how Yin and Yang vary depending on latitude. The latitude of a herb’s location determines the number of daylight hours and sunshine the herb is exposed to during the year. The number of daylight hours is one of the components affecting the concentration and composition of bioactive substances and therefore the efficacy of the herb. To standardize herbal preparation and administration, rigorous mathematical methods are essential to measure the Yin-Yang composition of herbs quantitatively. The work presented in this chapter is a first step toward such standardization. The chapter structure is as follows: Section 2 discusses the main ideas of the philosophical Yin-Yang concept. Section 3 shows today’s most common Yin-Yang symbol and discusses its typical shape. Then, Section 4 presents the origin of the Yin-Yang symbol and introduces a daylight model that allows computation of Yin and Yang depending on the daylight hours for each geographic latitude. Using the computed values for Yin and Yang, the section will show how to render the Yin-Yang symbol properly, and in accordance with its original meaning. The chapter concludes with a discussion of the consequences of the results for researchers in TCM and herbal medicine. Finally, the appendix contains examples of Yin-Yang symbols computed for different latitudes in the northern and southern hemispheres.