About 10% of the population is left-handed, including me. Preference for a particular hand does not emerge in children before age two years. The formal term for left-handed tendencies is sinistrality, which gives a clue as to how it was viewed at one time.
Four recent Presidents were or are left-handed: Gerald Ford, Ronald Reagan, Bill Clinton, and Barack Obama. In 2008, Obama's opponent, John McCain, was also left-handed.
At one time, left-handed children were coerced, or at least attempts were made, to coerce them to become right-handed. I'm glad that's not the case, although we live in a world that is more often engineered for right handers than for lefties. However, left-handed baseball batters need to take one less step in order to get to first base because they swing into the direction in which they are to run; this might give them a slight edge in getting on base.
There may be some other presumptions of "normality" that go beyond what is warranted, as the cartoon below hints.
Normality is not equivalent to statistical modality.