There is
evidence that both the north Asian and Indian
writing systems were
inspired, if not directly
adapted, through
trade with the Mesopotamians.
(... or vice versa...)
Besides, ya wank, you forgot Mayan glyphs, the most eminently provable case of parallel evolution of a writing system which clearly wasn't inspired through trade with other cultures. True, it is no longer in use and is mainly unknown, but that's not to say it doesn't exist.