Son has its roots in the meditative tradition of yoga which existed before Buddhism.
No one knows when yoga originated, but there is evidence that it is over five thousand years old.
Images of ascetics and gods seated in the lotus position of yoga can be found on seals and other relics excavated from the ruins of Mohenjodaro, a city of the Indus Valley civilization in India, which prospered in approximately 3000 B.C.
The son meditative tradition makes use of this sitting posture.