Although most people spend their entire lives following the biological impulse, it is only a tiny portion of our beings. If we remain obsessed with seeds and eggs, we are married to the fertile reproductive valley of the Mysterious Mother but not to her immeasureable heart and all-knowing mind
If you wish to unite with her heart and mind, you must integrate yin and yang within and refine their fire upward. Then you have the power to merge with the whole being of the Mysterious Mother. That is what is known as true evolution.
The first integration of yin and yang is the union of seed and egg within the womb. The second integration of yin and yang is the sexual union of the mature male and female. Both of these are concerned with flesh and blood, and all that is conceived in this realm must one day disintegrate and pass away.
It is only the third integration which gives birth to something immortal...The new life created by the final integration is self-aware without ego, capable of inhabiting a body yet not attached to it, and guided by wisdom rather than emotion. Whole and virtuous, it can never die.
Because higher and higher unions of yin and yang are necessary for the conception of life, some students may be instructed in the art of dual cultivation, in which yin and yang are directly integrated in the tai chi of sexual intercourse... If genuine virtue and true mastery come together... the practice can bring about a profound balancing of the student's gross and subtle energies.
The result of this is improved health, harmonised emotions, the cessation of cravings and impulses, and, at the highest level, the transcendent integration of the entire energy body.
- Hua Hu Ching, Lao Tzu