I have often wondered this myself, but generally come to the conclusion that though it is quite possible that in some cases the handedness of some influential person may have decided the handedness of script, this is unlikely as a rule.

Firstly although there are practical advantages to writing from left to right and top to bottom if one is right-handed, there is a tendency among children simply to go to the right at the start because it is superficially the handiest place. The greater convenience of starting at the left only becomes obvious later on, and without specific instruction, is easily overlooked.

Secondly, the way in which one starts to write (always assuming the absence of a recognised convention) is highly arbitrary, as one can see if one examines all the types of script that are generally recognised. Some write in rows from left to right, some from right to left, and some are boustrophedon, alternating from right to left and left to right. Boustrophedon incidentally, literally means "as the ploughing ox turns" in Greek, the language in which boustrophedon script originally was used (as far as I know anyway) and incidentally, to the trained eye it is quite an efficient mode for writing and reading. Whether it actually has material advantages over our current convention, I am not ready to guess.

However, there are still other ways of writing. Some cultures have written in spirals from inside out (now, there is a convention that makes sense; consider how difficult it would be a spiral from outside in!) And I do not know how many other conventions have been followed.

All the same, it does move me to suspect that the handedness of the original designers of our writing conventions did not in general reflect any special orientation of the convention that finally would be adopted in any particular case.

Of course, let me emphasise again that I have no special knowledge of the field; this is simply the result of uninformed speculation.

But I liked the question.

Cheers,

Jon