Does handedness have anything to do with the direction we read and write? Since English and European languages are read and written from left to right, are speakers of those languages more likely to be right handed than speakers of Semitic languages, which are read from right to left? That is, is the proportion of left-handers higher in the Middle East than in the West?
Also, is the proportion different for speakers of character languages like Japanese or Chinese? (I’m not sure if character language is the correct term.)
I have never heard of any indication that left-handedness is more prevalent among people who write right-to-left, and if anything due to cultural reasons there are fewer lefties actually expressing their left-handedness in those regions than in areas with European languages written left-to-right.
There was a time when Greek was written in alternating directions - right-to-left then the next line left-to-right - but Greeks are no more likely to be ambidextrous than anyone else. The wikipedia article references a couple other languages that did this as well.
There are also languages written vertically, and they can be either top-to-bottom or bottom-to-top, and the columns can go right-to-left or left-to-right.
Writing direction does not seem correlated with handedness.
Speaking as a left-hander, the son of a left-hander (who was “turned around”) and the father of a left-hander, I can tell you that handedness manifests itself before kids are taught to write. In my son’s case, it was pretty clear by the time he was four years old that he was left-handed. I suspect it was about the same for me, because when I started school my mother told the teacher something to the effect of, “Don’t you dare try to make him right-handed. You should see how they screwed up his father.”