From ‘The essential woman’ Elisabeth Rochat De La Vallee
In the 3rdcentury BCE the Chinese vision of the universe had the idea of an evolution within the natural cycle. (..) The ancient Chinese had the perspective that there were shifts in the natural order but that they were part of a greater order. Relating this to the body they saw there was constant change in the internal balance, with differences arising according to the time of day or time of the year. (..)
The second part of chapter 1 it states that there is a natural law giving a normal beginning and end to the ability to have children. This law is then elaborated, first for a woman progressing in periods of seven years, and afterwards for a man with periods of eight years.
(From Suwen chapter 1)“In general, the reproductive physiology of a woman is such that at 7 years of age her kidney energy becomes full, her permanent teeth come in, and her hair grows long. At fourteen years the tian kui, or fertility essence, matures, the ren/conception and the chong/vital channels responsible for conception open, menstruation begins, and conception is possible. At twenty-one years the kidney energy is strong and healthy, the wisdom teeth appear, and the body is vital and flourishing. At twenty-eighty years the bones and tendons are well developed and the hair and secondary sex characteristics are complete. This is the height of female development. At thirty-five the yangming/stomach and large intestine channels that govern the major facial muscles begin to atrophy, facial wrinkles appear, and the hair begins to thin. At forty-two all three yang channels -taiyang, shaoyang and yangming- are exhausted, the entire face is wrinkled, and the hair begins to turn gray. At forty-nine years the ren and the chong channels are completely empty, and the tian kui has dried up. Hence, the flow of the menses ceases and the woman is no longer able to conceive.
In the male, at eight years of age the kidney energy becomes full, the permanent teeth appear, and the hair becomes long. At sixteen years of age the kidney energy is ample, the tian kui is mature, and the jing is ripe, so procreation is possible. At twenty-four years the kidney qi is abundant, the bones and tendons grow strong, and the wisdom teeth come in. At the thirty-second year the body is at the peak of strength, and functions of the male are at their height. By forty the kidney qi begins to wane, teeth become loose, and the hair starts to fall. At forty-eight the yang energy of the head begins to deplete, the face becomes sallow, the hair grays, and the teeth deteriorate. BY fifty-six years the liver energy weakens, causing the tendons to stiffen. At sixty-four the tian kui dries up and the jing is drained, resulting in kidney exhaustion, fatigue, and weakness. When the energy of all the organ is full, the excess energy stored in the kidney is excreted for the purpose of conception. But now, the organs have aged and their energies have become depleted, the bones and tendons have become frail and stiff, and movements are hampered. The kidney reservoir becomes empty, marking the end of the power of conception.”
(..)The body of a woman and her whole physiology is predominantly yin and has more to do with the building and achievement of a form, while on the other hand a man has more to do with qi and initiating a process. (..) Seven and eight are numbers which were linked to the balance of yin and yang in ancient times. There are reference of this in several books, and even the Suwen other chapters, for example, chapter 5, allude to seven’s power to decrease and eight’s to increase. (..) More generally, this expression of increasing and decreasing is used for the balance of yin yang, especially related to sexuality and reproduction of life. Seven and height are another way to look at the movement of yin and yang and their balance in the body. However, the question as to why there is a yang number, seven, linked with women (and eight, yin, to men) is often asked. Why not to have a yin number to reflect a woman’s yin nature? The reason is that you need the dynamism of the yang inside the body of a woman in order to make things evolve.