Handedness comes in two groups, "right handed" and "not right handed." Most people use their right hands for almost all precision movement, but the other group is a broad spectrum from weakly-right to strongly-left. baen.com/handedness
The way we describe and define handedness creates the effect @CStuartHardwick rightly notices. Culture defines how we talk about it - but the behavior is mostly genetic. The % of righties has remained constant across continents and milennia.
Hand dominance is a more squirrelly thing than most people realize. For example, righties are better at *some* things with their left hand... and *some* of these asymmetries flip in lefties. Take a few minutes on #LeftHandersDay to learn more!
P.S. If you want to know why "some but not all of these asymmetries flip in lefties" (i.e. why lefties aren't just the reverse of righties), I discussed that not in any #NeuroThursday but in the article I linked above: baen.com/handedness
