This is how you become either right or left-handed.
This is how you become either right or left-handed. In fact, ultrasounds from week 13 of a pregnancy have revealed some babies already have a thumb-sucking preference dependent on which side is more dominant. Given you don't start learning to write until you're three or four, that's some head start in the right/left-handed stakes. http://ow.ly/s0cL30j8Qqb