righthandedness is more common because God is righthanded. How do we know? Look at the picture on the ceiling of the Sistine Chapel. He's reaching out to Adam with his (God's) right forefinger.
Witty -- but on that basis we'd have to conclude that mankind is lefthanded, because Michangelo's painting shows Adam touching God with his (Adam's) left hand. We might not trust Michaelangelo, however, for he also thought that Jews have horns on their heads (as appear on his statue of Moses).
(PS as to the latter: My understanding is that the Bible says that when Moses brought the Ten Commandments down from the mountain, rays of light were shining from his head. The Aramaic word for rays of light (halo) is "kerinim", and it has alternative meaning, "horns". When the Bible was first translated from Aramaic into Latin, the word was mis-translated as "horns" -- leading to the medieval belief that Jews have horns.)
EDIT upon checking the picture: on the ceiling of the Sistine Chapel. He's reaching out to Adam with his (God's) right forefinger, and His left arm proctively shelters a young woman (the future Eve?). Checking further, I found that in madonna and child paintings, the baby is almost always cradled in the left arm. Could it be that the right is active because the left (where the heart lies) (1) is the vulnerable side, needing protection, and (2) comforts the babe with the rhythm of the heartbeat? How does that square with the experience of any lefties in our group who have raised babes?