Presumably script that proceeds right to left (and even upwards) was originated by left handed scribes
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spellchecker : left handed scribes became left handed scones. The history of heavy baked goods in the development of human civilisation has been scandalously neglected by a blinkered academic community.
I remember I read somewhere about the fact that right-to-left script was preferred when carving script on stone. as right hand people supposedly prefer to hold the hammer on their right hand.
I'm not sure if that's really the cause. Furthermore in many ancient scripts the direction was quite unimportant, in some cases even reverting in each line (Boustrophedon).
edit spellchecker : left handed scribes became left handed scones. The history of heavy baked goods in the development of human civilisation has been scandalously neglected by a blinkered academic community.