It is believed the curtsey originated in certain parts of the further East and that the rationale behind it was as follows:

Human beings are the only creatures with an upright posture, and this is because they are the Axial being. When we bow we defer our axiality bringing the upper body nearer to the horizontal in homage to the verticality of another.

It is said that certain ancient Estrenne cultures held that blondes – being sacred – could never lose their axiality even relatively, thus they made reverence without inclining themselves toward the horizontal. In later times, of course, most curtseys came to incorporate some degree of inclination, but this is held – by some at least – to be their origin.

Incidentally, it is also said that the quasi-upright posture of birds when not in flight betokens their position as winged symbols of angelic powers.