There was travel and commerce between far out regions in that period (1,500-3,500 BCE). The connection between the three old-world starts of writing (Sumerian,

There was travel and commerce between far out regions in that period (1,500-3,500 BCE). The connection between the three old-world starts of writing (Sumerian, Egyptian and Chinese) is, AFAIK, not 100% clarified yet. It's widely accepted that American writing was a separate original invention, it makes sense. I believe these days the accepted understanding is that Egyptian hieroglyphic writing is an independent development that may, or may not, have been inspired by Sumerian writing. Not hard to believe: "you know son, these peoples far far away know magic, they're able to make dents in a table containing a story, and then pass on the tablet to someone else and they can retell the story!" Chinese writing may, or may not, have also come up the same way.