Amy Shea, Hoboken, New Jersey
Leslie Peters' reply:
By referring to Sirsasana (Headstand) and Sarvangasana (Shoulderstand) as the king and queen, or father and mother, of asanas, the ancient yogis were trying to make two points: These are important poses, and they are a pair. In certain systems of hatha yoga, these asanas are considered to be the very foundation upon which a yoga practice should be built, since the benefits one gets from practicing them are so great.
In his book Light on Yoga, B.K.S. Iyengar lists many ways that these two particular poses bring health and vitality to the practitioner. As for why Sirsasana is called the king, he explains that just as a country cannot thrive without a strong and effective king (or head of state), a person cannot thrive without a strong and healthy brain, which some yogis attribute to Sirsasana.
As for Sarvangasana, regular practice of it is thought to create harmony in the nervous and endocrine systems, just as a mother creates harmony in the home and the queen creates harmony in her country. (Apologies that both of these naming conventions could be interpreted as sexist.)
In addition to the many therapeutic benefits of Sarvangasana, it is considered an essential pose for several reasons: It is learned before Sirsasana, it is a more complex and sophisticated pose than Sirsasana, and although one can practice Sarvangasana independent of Sirsasana, the reverse is not encouraged, which makes Sarvangasana, like a mother, indispensable.
While both poses bring poise, vibrancy, and health to the practitioner, they do it in different ways. Sirsasana heats the body, and Sarvangasana cools it. To achieve the balance we seek through yoga, it's important to have both.
Leslie Peters is a certified intermediate Iyengar Yoga teacher and the former director of the Iyengar Yoga Institute of Los Angeles. She is featured in the book Yoga: The Path to Holistic Health, by B.K.S. Iyengar.