Being a left hander, I have always tried to find reasons to why that is. Theories seek to explain the dominance of one hand either in terms of environment and upbringing or through a gene-based hereditary chain. No gene for left-handedness has been found yet, but here are a few theories:

• Sun-worship, with most of mankind being in the Northern hemisphere and following the sun across the sky from left to right, established right as a favored direction, leading to right hand dominance
• The use of a shield in the left hand to protect the heart on the left side of the body led to the right hand being used to hold weapons, which led to general right dominance
• At birth babies are neither left or right handed and the actions of those around them will educate them into one side being dominant
• Left Handedness is hereditary, transmitted from parents to children
• Left Handedness is controlled by a genetic bias, which is random but favors a right-hand dominance

Any other theory you might be able to add?