daniel p wrote:
Given the emphasis on sitting meditation within the Buddhist tradition I'm surprised so little is said about it, the history, the reasons for the various postures, the hands, the appropriate way to sit. Just the basic physical mechanical aspect. 2500 years experience should yield something.
Where's the manual on best practice?
The history as the Bodhisatta would have come upon it is possibly encapsulated by the formless attainments; see The Origin of Buddhist Meditation
by A. Wynne. In any event, it was certainly an early Upanisadic milieu.
If, by the 'various postures' you mean things such as lotus, half-lotus, Burmese, seiza, and so on, those are all simple variations with no functional purpose apart from which style suits ones individual physiology. India circa 400 BCE was largely a place of sitting on the ground, whereupon "folding legs under" was a simple call to sit normally (!) without ones legs thrown askew, and "setting ones back straight" was a simple call not to slouch in order to prevent back strain and facilitate sitting for long periods. It's akin to a recipe on how to make a peanut butter sandwich. The first instruction is not a method to make bread from scratch, because it's assumed the bread is common and at hand. So, too, sitting on the ground.
(An esotericist will accept special significance for a straight back, usually involving either the chakras or the meridians. On a related note, gently resting your tongue somewhere on the roof of your mouth can prevent saliva from accumulating and leading to distracting/frequent swallowing, yet here again an esotericist will observe an important energetic function for this meditative tool.)
The hands needn't be in any mudra or any particular place, but they should rest gently in the lap such that (a) the shoulders aren't twisted into shoulder- and back-wearying shapes, allowing them to be down and away from the ears to prevent neck tension, and (b) you don't fidget with them (as can happen, for example, when trying to make kuji-kiri or mimic buddharupas). As always, the primary goal for the body is the ability to relax without inviting sloth-&-torpor (thīna-middha), ultimately leading to a habitual seated posture that can be assumed and maintained without the flurry-and-worry (uddhacca-kukkucca) of the beginner.