Two bits of information, one from a direct source, the other from
speculation, re the predominance:
1. A member of my church came back from the Phillipines with a left/right
story:
1a. Since there traditionally hasn’t been toilet paper in many places, and
the available foliage was not great, after defacating, people always
used their left hands for wiping, and generally considered the left hand
relatively unclean; plus
1b. Since there was little in the way of cutlery etc, it was common to take a
handful of of the bowl, and bring it to the mouth… this was always done
with the right hand, since it was more hygenic than the left.
1c. (Bonus comment): Apparently (I’m not sure if my sources are accurate)
the right-hand-scoop-from-bowl-to-opening-mouth seems to be quite a
low-level instinct, and can be sometimes seen even in cases of significant
damage to higher functional areas of the brain.
2. The other story I’ve heard, long ago, was that the right hand was the hand for
for holding a weapon (sword), and so a proffered-empty right hand, for a
handshake, was a signal of non-aggression.
Sonoran Conservative 
They’re funnier when literally translated: “ambidextrous” = “both right hands”, the other one = “both left hands”.
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Two bits of information, one from a direct source, the other from
speculation, re the predominance:
1. A member of my church came back from the Phillipines with a left/right
story:
1a. Since there traditionally hasn’t been toilet paper in many places, and
the available foliage was not great, after defacating, people always
used their left hands for wiping, and generally considered the left hand
relatively unclean; plus
1b. Since there was little in the way of cutlery etc, it was common to take a
handful of of the bowl, and bring it to the mouth… this was always done
with the right hand, since it was more hygenic than the left.
1c. (Bonus comment): Apparently (I’m not sure if my sources are accurate)
the right-hand-scoop-from-bowl-to-opening-mouth seems to be quite a
low-level instinct, and can be sometimes seen even in cases of significant
damage to higher functional areas of the brain.
2. The other story I’ve heard, long ago, was that the right hand was the hand for
for holding a weapon (sword), and so a proffered-empty right hand, for a
handshake, was a signal of non-aggression.
— Abstemious and Facetious
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The Latin for “right” is “dexter”, whereas the Latin for “left” is “sinere”.
So, right-handed people are “dextrous”… while left-handed people are “sinister”.
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